The personal website of Scott W Harden
March 28th, 2023

Treemapping with C#

Treemap diagrams display a series of positive numbers using rectangles sized proportional to the value of each number. This page demonstrates how to calculate the size and location of rectangles to create a tree map diagram using C#. Although the following uses System.Drawing to save the tree map as a Bitmap image, these concepts may be combined with information on the C# Data Visualization page to create treemap diagrams using SkiaSharp, WPF, or other graphics technologies.

The tree map above was generated from random data using the following C# code:

// Create sample data. Data must be sorted large to small.
double[] sortedValues = Enumerable.Range(0, 40)
    .Select(x => (double)Random.Shared.Next(10, 100))
    .OrderByDescending(x => x)
    .ToArray();

// Create an array of labels in the same order as the sorted data.
string[] labels = sortedValues.Select(x => x.ToString()).ToArray();

// Calculate the size and position of all rectangles in the tree map
int width = 600;
int height = 400;
RectangleF[] rectangles = TreeMap.GetRectangles(sortedValues, width, height);

// Create an image to draw on (with 1px extra to make room for the outline)
using Bitmap bmp = new(width + 1, height + 1);
using Graphics gfx = Graphics.FromImage(bmp);
using Font fnt = new("Consolas", 8);
using SolidBrush brush = new(Color.Black);
gfx.Clear(Color.White);

// Draw and label each rectangle
for (int i = 0; i < rectangles.Length; i++)
{
    brush.Color = Color.FromArgb(
        red: Random.Shared.Next(150, 250),
        green: Random.Shared.Next(150, 250),
        blue: Random.Shared.Next(150, 250));

    gfx.FillRectangle(brush, rectangles[i]);
    gfx.DrawRectangle(Pens.Black, rectangles[i]);
    gfx.DrawString(labels[i], fnt, Brushes.Black, rectangles[i].X, rectangles[i].Y);
}

// Save the output
bmp.Save("treemap.bmp");

Treemap Logic

The previous code block focuses on data generation and display, but hides the tree map calculations behind the TreeMap class. Below is the code for that class. It is self-contained static class and exposes a single static method which takes a pre-sorted array of values and returns tree map rectangles ready to display on an image.

💡 Although the System.Drawing.Common is a Windows-only library (as of .NET 7), System.Drawing.Primitives is a cross-platform package that provides the RectangleF structure used in the tree map class. See the SkiaSharp Quickstart to learn how to create image files using cross-platform .NET code.

public static class TreeMap
{
    public static RectangleF[] GetRectangles(double[] values, int width, int height)
    {
        for (int i = 1; i < values.Length; i++)
            if (values[i] > values[i - 1])
                throw new ArgumentException("values must be ordered large to small");

        var slice = GetSlice(values, 1, 0.35);
        var rectangles = GetRectangles(slice, width, height);
        return rectangles.Select(x => x.ToRectF()).ToArray();
    }

    private class Slice
    {
        public double Size { get; }
        public IEnumerable<double> Values { get; }
        public Slice[] Children { get; }

        public Slice(double size, IEnumerable<double> values, Slice sub1, Slice sub2)
        {
            Size = size;
            Values = values;
            Children = new Slice[] { sub1, sub2 };
        }

        public Slice(double size, double finalValue)
        {
            Size = size;
            Values = new double[] { finalValue };
            Children = Array.Empty<Slice>();
        }
    }

    private class SliceResult
    {
        public double ElementsSize { get; }
        public IEnumerable<double> Elements { get; }
        public IEnumerable<double> RemainingElements { get; }

        public SliceResult(double elementsSize, IEnumerable<double> elements, IEnumerable<double> remainingElements)
        {
            ElementsSize = elementsSize;
            Elements = elements;
            RemainingElements = remainingElements;
        }
    }

    private class SliceRectangle
    {
        public Slice Slice { get; set; }
        public float X { get; set; }
        public float Y { get; set; }
        public float Width { get; set; }
        public float Height { get; set; }
        public SliceRectangle(Slice slice) => Slice = slice;
        public RectangleF ToRectF() => new(X, Y, Width, Height);
    }

    private static Slice GetSlice(IEnumerable<double> elements, double totalSize, double sliceWidth)
    {
        if (elements.Count() == 1)
            return new Slice(totalSize, elements.Single());

        SliceResult sr = GetElementsForSlice(elements, sliceWidth);
        Slice child1 = GetSlice(sr.Elements, sr.ElementsSize, sliceWidth);
        Slice child2 = GetSlice(sr.RemainingElements, 1 - sr.ElementsSize, sliceWidth);
        return new Slice(totalSize, elements, child1, child2);
    }

    private static SliceResult GetElementsForSlice(IEnumerable<double> elements, double sliceWidth)
    {
        var elementsInSlice = new List<double>();
        var remainingElements = new List<double>();
        double current = 0;
        double total = elements.Sum();

        foreach (var element in elements)
        {
            if (current > sliceWidth)
                remainingElements.Add(element);
            else
            {
                elementsInSlice.Add(element);
                current += element / total;
            }
        }

        return new SliceResult(current, elementsInSlice, remainingElements);
    }

    private static IEnumerable<SliceRectangle> GetRectangles(Slice slice, int width, int height)
    {
        SliceRectangle area = new(slice) { Width = width, Height = height };

        foreach (var rect in GetRectangles(area))
        {
            if (rect.X + rect.Width > area.Width)
                rect.Width = area.Width - rect.X;

            if (rect.Y + rect.Height > area.Height)
                rect.Height = area.Height - rect.Y;

            yield return rect;
        }
    }

    private static IEnumerable<SliceRectangle> GetRectangles(SliceRectangle sliceRectangle)
    {
        var isHorizontalSplit = sliceRectangle.Width >= sliceRectangle.Height;
        var currentPos = 0;
        foreach (var subSlice in sliceRectangle.Slice.Children)
        {
            var subRect = new SliceRectangle(subSlice);
            int rectSize;

            if (isHorizontalSplit)
            {
                rectSize = (int)Math.Round(sliceRectangle.Width * subSlice.Size);
                subRect.X = sliceRectangle.X + currentPos;
                subRect.Y = sliceRectangle.Y;
                subRect.Width = rectSize;
                subRect.Height = sliceRectangle.Height;
            }
            else
            {
                rectSize = (int)Math.Round(sliceRectangle.Height * subSlice.Size);
                subRect.X = sliceRectangle.X;
                subRect.Y = sliceRectangle.Y + currentPos;
                subRect.Width = sliceRectangle.Width;
                subRect.Height = rectSize;
            }

            currentPos += rectSize;

            if (subSlice.Values.Count() > 1)
            {
                foreach (var sr in GetRectangles(subRect))
                {
                    yield return sr;
                }
            }
            else if (subSlice.Values.Count() == 1)
            {
                yield return subRect;
            }
        }
    }
}

Source Code Complexity Analysis

A few days ago I wrote an article describing how to programmatically generate .NET source code analytics using C#. Using these tools I analyzed the source code for all classes in a large project (ScottPlot.NET). The following tree map displays every class in the project as a rectangle sized according to number of lines of code and colored according to maintainability.

In this diagram large rectangles represent classes with the most code, and red color indicates classes that are difficult to maintain.

💡 I'm using a perceptually uniform colormap (similar to Turbo)provided by the ScottPlot provided by the ScottPlot NuGet package. See ScottPlot's colormaps gallery for all available colormaps.

💡 The Maintainability Index is a value between 0 (worst) and 100 (best) that represents the relative ease of maintaining the code. It's calculated from a combination of Halstead complexity (size of the compiled code), Cyclomatic complexity (number of paths that can be taken through the code), and the total number of lines of code.

Conclusions

  • Generation of tree map diagrams can be achieved using recursive programming

  • The static class above makes it easy to generate tree maps in C#

  • ScottPlot's AxisTicksRender class may be difficult to maintain

References

Markdown source code last modified on March 8th, 2023
---
Title: Treemapping with C#
Description: How to create a treemap diagram using C#
Date: 2023-03-28 00:32AM EST
Tags: csharp, graphics
---

# Treemapping with C# 

**Treemap diagrams display a series of positive numbers using rectangles sized proportional to the value of each number.** This page demonstrates how to calculate the size and location of rectangles to create a tree map diagram using C#. Although the following uses System.Drawing to save the tree map as a Bitmap image, these concepts may be combined with information on the [C# Data Visualization](https://swharden.com/csdv/) page to create treemap diagrams using SkiaSharp, WPF, or other graphics technologies.

<img src="treemap.png" class="img-fluid d-block mx-auto shadow my-5">

The tree map above was generated from random data using the following C# code:

```cs
// Create sample data. Data must be sorted large to small.
double[] sortedValues = Enumerable.Range(0, 40)
    .Select(x => (double)Random.Shared.Next(10, 100))
    .OrderByDescending(x => x)
    .ToArray();

// Create an array of labels in the same order as the sorted data.
string[] labels = sortedValues.Select(x => x.ToString()).ToArray();

// Calculate the size and position of all rectangles in the tree map
int width = 600;
int height = 400;
RectangleF[] rectangles = TreeMap.GetRectangles(sortedValues, width, height);

// Create an image to draw on (with 1px extra to make room for the outline)
using Bitmap bmp = new(width + 1, height + 1);
using Graphics gfx = Graphics.FromImage(bmp);
using Font fnt = new("Consolas", 8);
using SolidBrush brush = new(Color.Black);
gfx.Clear(Color.White);

// Draw and label each rectangle
for (int i = 0; i < rectangles.Length; i++)
{
    brush.Color = Color.FromArgb(
        red: Random.Shared.Next(150, 250),
        green: Random.Shared.Next(150, 250),
        blue: Random.Shared.Next(150, 250));

    gfx.FillRectangle(brush, rectangles[i]);
    gfx.DrawRectangle(Pens.Black, rectangles[i]);
    gfx.DrawString(labels[i], fnt, Brushes.Black, rectangles[i].X, rectangles[i].Y);
}

// Save the output
bmp.Save("treemap.bmp");
```

## Treemap Logic

The previous code block focuses on data generation and display, but hides the tree map calculations behind the `TreeMap` class. Below is the code for that class. It is self-contained static class and exposes a single static method which takes a pre-sorted array of values and returns tree map rectangles ready to display on an image.

> 💡 Although the `System.Drawing.Common` is a Windows-only library ([as of .NET 7](https://github.com/dotnet/designs/blob/main/accepted/2021/system-drawing-win-only/system-drawing-win-only.md)), `System.Drawing.Primitives` is a cross-platform package that provides the `RectangleF` structure used in the tree map class. See the [SkiaSharp Quickstart](https://swharden.com/csdv/skiasharp/quickstart-console/) to learn how to create image files using cross-platform .NET code.

```cs
public static class TreeMap
{
    public static RectangleF[] GetRectangles(double[] values, int width, int height)
    {
        for (int i = 1; i < values.Length; i++)
            if (values[i] > values[i - 1])
                throw new ArgumentException("values must be ordered large to small");

        var slice = GetSlice(values, 1, 0.35);
        var rectangles = GetRectangles(slice, width, height);
        return rectangles.Select(x => x.ToRectF()).ToArray();
    }

    private class Slice
    {
        public double Size { get; }
        public IEnumerable<double> Values { get; }
        public Slice[] Children { get; }

        public Slice(double size, IEnumerable<double> values, Slice sub1, Slice sub2)
        {
            Size = size;
            Values = values;
            Children = new Slice[] { sub1, sub2 };
        }

        public Slice(double size, double finalValue)
        {
            Size = size;
            Values = new double[] { finalValue };
            Children = Array.Empty<Slice>();
        }
    }

    private class SliceResult
    {
        public double ElementsSize { get; }
        public IEnumerable<double> Elements { get; }
        public IEnumerable<double> RemainingElements { get; }

        public SliceResult(double elementsSize, IEnumerable<double> elements, IEnumerable<double> remainingElements)
        {
            ElementsSize = elementsSize;
            Elements = elements;
            RemainingElements = remainingElements;
        }
    }

    private class SliceRectangle
    {
        public Slice Slice { get; set; }
        public float X { get; set; }
        public float Y { get; set; }
        public float Width { get; set; }
        public float Height { get; set; }
        public SliceRectangle(Slice slice) => Slice = slice;
        public RectangleF ToRectF() => new(X, Y, Width, Height);
    }

    private static Slice GetSlice(IEnumerable<double> elements, double totalSize, double sliceWidth)
    {
        if (elements.Count() == 1)
            return new Slice(totalSize, elements.Single());

        SliceResult sr = GetElementsForSlice(elements, sliceWidth);
        Slice child1 = GetSlice(sr.Elements, sr.ElementsSize, sliceWidth);
        Slice child2 = GetSlice(sr.RemainingElements, 1 - sr.ElementsSize, sliceWidth);
        return new Slice(totalSize, elements, child1, child2);
    }

    private static SliceResult GetElementsForSlice(IEnumerable<double> elements, double sliceWidth)
    {
        var elementsInSlice = new List<double>();
        var remainingElements = new List<double>();
        double current = 0;
        double total = elements.Sum();

        foreach (var element in elements)
        {
            if (current > sliceWidth)
                remainingElements.Add(element);
            else
            {
                elementsInSlice.Add(element);
                current += element / total;
            }
        }

        return new SliceResult(current, elementsInSlice, remainingElements);
    }

    private static IEnumerable<SliceRectangle> GetRectangles(Slice slice, int width, int height)
    {
        SliceRectangle area = new(slice) { Width = width, Height = height };

        foreach (var rect in GetRectangles(area))
        {
            if (rect.X + rect.Width > area.Width)
                rect.Width = area.Width - rect.X;

            if (rect.Y + rect.Height > area.Height)
                rect.Height = area.Height - rect.Y;

            yield return rect;
        }
    }

    private static IEnumerable<SliceRectangle> GetRectangles(SliceRectangle sliceRectangle)
    {
        var isHorizontalSplit = sliceRectangle.Width >= sliceRectangle.Height;
        var currentPos = 0;
        foreach (var subSlice in sliceRectangle.Slice.Children)
        {
            var subRect = new SliceRectangle(subSlice);
            int rectSize;

            if (isHorizontalSplit)
            {
                rectSize = (int)Math.Round(sliceRectangle.Width * subSlice.Size);
                subRect.X = sliceRectangle.X + currentPos;
                subRect.Y = sliceRectangle.Y;
                subRect.Width = rectSize;
                subRect.Height = sliceRectangle.Height;
            }
            else
            {
                rectSize = (int)Math.Round(sliceRectangle.Height * subSlice.Size);
                subRect.X = sliceRectangle.X;
                subRect.Y = sliceRectangle.Y + currentPos;
                subRect.Width = sliceRectangle.Width;
                subRect.Height = rectSize;
            }

            currentPos += rectSize;

            if (subSlice.Values.Count() > 1)
            {
                foreach (var sr in GetRectangles(subRect))
                {
                    yield return sr;
                }
            }
            else if (subSlice.Values.Count() == 1)
            {
                yield return subRect;
            }
        }
    }
}
```

## Source Code Complexity Analysis

A few days ago I wrote an article describing how to [programmatically generate .NET source code analytics using C#](https://swharden.com/blog/2023-03-05-dotnet-code-analysis/). Using these tools I analyzed the source code for all classes in a large project ([ScottPlot.NET](https://scottplot.net)). The following tree map displays every class in the project as a rectangle sized according to number of lines of code and colored according to maintainability. 

<a href="code-report.png"><img src="code-report.png" class="img-fluid d-inline-block mx-auto shadow mt-5"></a>

<img src="turbo.png" class="img-fluid d-inline-block mx-auto shadow mb-5">

In this diagram large rectangles represent classes with the most code, and red color indicates classes that are difficult to maintain. 

> 💡 I'm using a perceptually uniform colormap (similar to [Turbo](https://ai.googleblog.com/2019/08/turbo-improved-rainbow-colormap-for.html))provided by the [ScottPlot](https://scottplot.net) provided by the [ScottPlot](https://scottplot.net) NuGet package. See ScottPlot's [colormaps gallery](https://scottplot.net/cookbook/4.1/colormaps/) for all available colormaps.

> 💡 The [Maintainability Index](https://learn.microsoft.com/en-us/visualstudio/code-quality/code-metrics-maintainability-index-range-and-meaning) is a value between 0 (worst) and 100 (best) that represents the relative ease of maintaining the code. It's calculated from a combination of [Halstead complexity](https://en.wikipedia.org/wiki/Halstead_complexity_measures) (size of the compiled code), [Cyclomatic complexity](https://en.wikipedia.org/wiki/Cyclomatic_complexity) (number of paths that can be taken through the code), and the total number of lines of code.

## Conclusions

* Generation of tree map diagrams can be achieved using recursive programming

* The static class above makes it easy to generate tree maps in C#

* ScottPlot's AxisTicksRender class may be difficult to maintain

## References

* This blog post is spillover from ScottPlot issues [#1479](https://github.com/ScottPlot/ScottPlot/issues/1479) and [#2454](https://github.com/ScottPlot/ScottPlot/issues/2454).

* Code here was heavily influenced by [The Never Ending Journey](http://pascallaurin42.blogspot.com/2013/12/implementing-treemap-in-c.html) (Dec 29, 2013)

* [Treemapping](https://en.wikipedia.org/wiki/Treemapping) (Wikipedia)

* [D3 Treemap](https://d3-graph-gallery.com/treemap.html)

* [Squarified Treemaps](https://www.win.tue.nl/~vanwijk/stm.pdf) (Bruls et al.)

* StackOverflow question [32548949](https://stackoverflow.com/questions/32548949/from-c-sharp-serverside-is-there-anyway-to-generate-a-treemap-and-save-as-an-im/37154938#37154938)

* [C# Data Visualization](https://swharden.com/csdv/)
March 5th, 2023

Generate .NET Code Metrics from Console Applications

This page describes how to use the Microsoft.CodeAnalysis.Metrics package to perform source code analysis of .NET assemblies from a console application. Visual Studio users can perform source code analysis by clicking the "Analyze" dropdown menu and selecting "Calculate Code Metrics", but I sought to automate this process so I can generate custom code analysis reports from console applications as part of my CI pipeline.

Performing Code Analysis

Step 1: Add the Microsoft.CodeAnalysis.Metrics package to your project:

dotnet add package Microsoft.CodeAnalysis.Metrics

Step 2: Perform code analysis:

dotnet build -target:Metrics

Note that multi-targeted projects must append --framework net6.0 to specify a single platform target to use for code analysis.

Step 3: Inspect analysis results in ProjectName.Metrics.xml

<?xml version="1.0" encoding="utf-8"?>
<CodeMetricsReport Version="1.0">
  <Targets>
    <Target Name="ScottPlot.csproj">
      <Assembly Name="ScottPlot, Version=4.1.61.0">
        <Metrics>
          <Metric Name="MaintainabilityIndex" Value="81" />
          <Metric Name="CyclomaticComplexity" Value="6324" />
          <Metric Name="ClassCoupling" Value="664" />
          <Metric Name="DepthOfInheritance" Value="3" />
          <Metric Name="SourceLines" Value="35360" />
          <Metric Name="ExecutableLines" Value="10208" />
        </Metrics>
        <Namespaces>
        ...

Parsing the Analysis XML File

The code analysis XML contains information about every assembly, namespace, type, and function in the whole code base! There is a lot of possible information to extract, but the code below is enough to get us started extracting basic metric information for every type in the code base.

using System;
using System.IO;
using System.Linq;
using System.Text;
using System.Xml.Linq;
using System.Collections.Generic;

/// <summary>
/// Display a particular metric for every type in an assembly.
/// </summary>
void RankTypes(string xmlFilePath, string metricName = "CyclomaticComplexity", bool highToLow = true)
{
    string xmlText = File.ReadAllText(xmlFilePath);
    XDocument doc = XDocument.Parse(xmlText);
    XElement assembly = doc.Descendants("Assembly").First();

    var rankedTypes = GetMetricByType(assembly, metricName).OrderBy(x => x.Value).ToArray();
    if (highToLow)
        Array.Reverse(rankedTypes);

    Console.WriteLine($"Types ranked by {metricName}:");
    foreach (var type in rankedTypes)
        Console.WriteLine($"{type.Value:N0}\t{type.Key}");
}

Dictionary<string, int> GetMetricByType(XElement assembly, string metricName)
{
    Dictionary<string, int> metricByType = new();

    foreach (XElement namespaceElement in assembly.Element("Namespaces")!.Elements("Namespace"))
    {
        foreach (XElement namedType in namespaceElement.Elements("Types").Elements("NamedType"))
        {
            XElement metric = namedType.Element("Metrics")!.Elements("Metric")
                .Where(x => x.Attribute("Name")!.Value == metricName)
                .Single();
            string typeName = namedType.Attribute("Name")!.Value;
            string namespaceName = namespaceElement.Attribute("Name")!.Value;
            string fullTypeName = $"{namespaceName}.{typeName}";
            metricByType[fullTypeName] = int.Parse(metric.Attribute("Value")!.Value!.ToString());
        }
    }

    return metricByType;
}

Querying Code Analysis Results

Specific metrics of interest will vary, but here are some code examples demonstrating how to parse the code metrics file to display useful information. For these examples I run the code analysis command above to generate ScottPlot.Metrics.xml from the ScottPlot code base and use the code above to generate various reports.

Rank Types by Cyclomatic Complexity

Cyclomatic complexity is a measure of the number of different paths that can be taken through a computer program, and it is often used as an indicator for difficult-to-maintain code. Some CI systems even prevent the merging of pull requests if their cyclomatic complexity exceeds a predefined threshold! Although I don't intend to gate pull requests by complexity at this time, I would like to gain insight into which classes are the most complex as a way to quantitatively target my code maintenance and efforts.

RankTypes("ScottPlot.Metrics.xml", "CyclomaticComplexity");
517     ScottPlot.Plot
218     ScottPlot.Plottable.SignalPlotBase<T>
173     ScottPlot.Plottable.ScatterPlot
139     ScottPlot.Settings
120     ScottPlot.Ticks.TickCollection
118     ScottPlot.Renderable.Axis
114     ScottPlot.Drawing.Colormap
113     ScottPlot.Control.ControlBackEnd
109     ScottPlot.DataGen
99      ScottPlot.Plottable.AxisLineVector
98      ScottPlot.Plottable.Heatmap
95      ScottPlot.Tools
93      ScottPlot.Plottable.RepeatingAxisLine
91      ScottPlot.Plottable.PopulationPlot
85      ScottPlot.Plottable.AxisLine
83      ScottPlot.Plottable.AxisSpan
77      ScottPlot.Plottable.RadialGaugePlot
...

Rank Types by Lines of Code

Similarly, ranking all my project's types by how many lines of code they contain can give me insight into which types may benefit most from refactoring.

RankTypes("ScottPlot.Metrics.xml", "SourceLines");
Types ranked by SourceLines:
4,155   ScottPlot.Plot
1,182   ScottPlot.DataGen
954     ScottPlot.Plottable.SignalPlotBase<T>
726     ScottPlot.Control.ControlBackEnd
670     ScottPlot.Ticks.TickCollection
670     ScottPlot.Settings
630     ScottPlot.Plottable.ScatterPlot
600     ScottPlot.Renderable.Axis
477     ScottPlot.Statistics.Common
454     ScottPlot.Tools
451     ScottPlot.Plottable.PopulationPlot
432     ScottPlot.Drawing.GDI
343     ScottPlot.Plottable.SignalPlotXYGeneric<TX, TY>
336     ScottPlot.Plottable.RepeatingAxisLine
335     ScottPlot.Drawing.Colormap
332     ScottPlot.Plottable.AxisLineVector
...

Rank Types by Maintainability

The Maintainability Index is a value between 0 (worst) and 100 (best) that represents the relative ease of maintaining the code. It's calculated from a combination of Halstead complexity (size of the compiled code), Cyclomatic complexity (number of paths that can be taken through the code), and the total number of lines of code.

MaintainabilityIndex = 171 
  - 5.2 * Math.Log(HalsteadVolume) 
  - 0.23 * CyclomaticComplexity
  - 16.2 * Math.Log(LinesOfCCode);

The maintainability index is calculated by Microsoft.CodeAnalysis.Metrics so we don't have to. I don't know how Microsoft arrived at their weights for this formula, but the overall idea is described here.

RankTypes("ScottPlot.Metrics.xml", "MaintainabilityIndex", highToLow: false);
43      ScottPlot.Drawing.Tools
48      ScottPlot.Statistics.Interpolation.Cubic
48      ScottPlot.Statistics.Interpolation.PeriodicSpline
49      ScottPlot.Statistics.Interpolation.EndSlopeSpline
49      ScottPlot.Statistics.Interpolation.NaturalSpline
50      ScottPlot.Renderable.AxisTicksRender
54      ScottPlot.Statistics.Interpolation.CatmullRom
55      ScottPlot.Statistics.Interpolation.SplineInterpolator
57      ScottPlot.DataGen
58      ScottPlot.DataStructures.SegmentedTree<T>
58      ScottPlot.MarkerShapes.Hashtag
58      ScottPlot.Ticks.TickCollection
59      ScottPlot.MarkerShapes.Asterisk
59      ScottPlot.Plottable.SignalPlotXYGeneric<TX, TY>
59      ScottPlot.Statistics.Interpolation.Bezier
60      ScottPlot.Statistics.Interpolation.Chaikin
61      ScottPlot.Generate
61      ScottPlot.Plot
61      ScottPlot.Statistics.Finance
...

Create Custom HTML Reports

With a little more effort you can generate HTML reports that use tables and headings to highlight useful code metrics and draw attention to types that could benefit from refactoring to improve maintainability.

Conclusions

Microsoft's official Microsoft.CodeAnalysis.Metrics NuGet package is a useful tool for analyzing assemblies, navigating through namespaces, types, properties, and methods, and evaluating their metrics. Since these analyses can be performed using console applications, they can be easily integrated into CI pipelines or used to create standalone code analysis applications. Future projects can build on the concepts described here to create graphical visualizations of code metrics in large projects.

Resources

Markdown source code last modified on March 5th, 2023
---
Title: .NET Source Code Analysis
Description: How to analyze source code metrics of .NET assemblies from a console application
Date: 2023-03-05 3:20PM EST
Tags: csharp
---

# Generate .NET Code Metrics from Console Applications

**This page describes how to use the [Microsoft.CodeAnalysis.Metrics](https://www.nuget.org/packages/Microsoft.CodeAnalysis.Metrics/) package to perform source code analysis of .NET assemblies from a console application.** Visual Studio users can perform source code analysis by clicking the "Analyze" dropdown menu and selecting "Calculate Code Metrics", but I sought to automate this process so I can generate custom code analysis reports from console applications as part of my CI pipeline.

## Performing Code Analysis

**Step 1:** Add the [`Microsoft.CodeAnalysis.Metrics`](https://www.nuget.org/packages/Microsoft.CodeAnalysis.Metrics/) package to your project:

```bash
dotnet add package Microsoft.CodeAnalysis.Metrics
```

**Step 2:** Perform code analysis:

```bash
dotnet build -target:Metrics
```

Note that multi-targeted projects must append `--framework net6.0` to specify a single platform target to use for code analysis.

**Step 3:** Inspect analysis results in `ProjectName.Metrics.xml`

```xml
<?xml version="1.0" encoding="utf-8"?>
<CodeMetricsReport Version="1.0">
  <Targets>
    <Target Name="ScottPlot.csproj">
      <Assembly Name="ScottPlot, Version=4.1.61.0">
        <Metrics>
          <Metric Name="MaintainabilityIndex" Value="81" />
          <Metric Name="CyclomaticComplexity" Value="6324" />
          <Metric Name="ClassCoupling" Value="664" />
          <Metric Name="DepthOfInheritance" Value="3" />
          <Metric Name="SourceLines" Value="35360" />
          <Metric Name="ExecutableLines" Value="10208" />
        </Metrics>
        <Namespaces>
        ...
```

## Parsing the Analysis XML File

The code analysis XML contains information about every assembly, namespace, type, and function in the whole code base! There is a lot of possible information to extract, but the code below is enough to get us started extracting basic metric information for every type in the code base.

```cs
using System;
using System.IO;
using System.Linq;
using System.Text;
using System.Xml.Linq;
using System.Collections.Generic;

/// <summary>
/// Display a particular metric for every type in an assembly.
/// </summary>
void RankTypes(string xmlFilePath, string metricName = "CyclomaticComplexity", bool highToLow = true)
{
    string xmlText = File.ReadAllText(xmlFilePath);
    XDocument doc = XDocument.Parse(xmlText);
    XElement assembly = doc.Descendants("Assembly").First();

    var rankedTypes = GetMetricByType(assembly, metricName).OrderBy(x => x.Value).ToArray();
    if (highToLow)
        Array.Reverse(rankedTypes);

    Console.WriteLine($"Types ranked by {metricName}:");
    foreach (var type in rankedTypes)
        Console.WriteLine($"{type.Value:N0}\t{type.Key}");
}

Dictionary<string, int> GetMetricByType(XElement assembly, string metricName)
{
    Dictionary<string, int> metricByType = new();

    foreach (XElement namespaceElement in assembly.Element("Namespaces")!.Elements("Namespace"))
    {
        foreach (XElement namedType in namespaceElement.Elements("Types").Elements("NamedType"))
        {
            XElement metric = namedType.Element("Metrics")!.Elements("Metric")
                .Where(x => x.Attribute("Name")!.Value == metricName)
                .Single();
            string typeName = namedType.Attribute("Name")!.Value;
            string namespaceName = namespaceElement.Attribute("Name")!.Value;
            string fullTypeName = $"{namespaceName}.{typeName}";
            metricByType[fullTypeName] = int.Parse(metric.Attribute("Value")!.Value!.ToString());
        }
    }

    return metricByType;
}
```

## Querying Code Analysis Results

**Specific metrics of interest will vary, but here are some code examples demonstrating how to parse the code metrics file to display useful information.** For these examples I run the code analysis command above to generate [ScottPlot.Metrics.xml](ScottPlot.Metrics.xml.zip) from the [ScottPlot](https://scottplot.net) code base and use the code above to generate various reports.

### Rank Types by Cyclomatic Complexity

[Cyclomatic complexity](https://en.wikipedia.org/wiki/Cyclomatic_complexity) is a measure of the number of different paths that can be taken through a computer program, and it is often used as an indicator for difficult-to-maintain code. Some CI systems even prevent the merging of pull requests if their cyclomatic complexity exceeds a predefined threshold! Although I don't intend to gate pull requests by complexity at this time, I would like to gain insight into which classes are the most complex as a way to quantitatively target my code maintenance and efforts.

```cs
RankTypes("ScottPlot.Metrics.xml", "CyclomaticComplexity");
```

```txt
517     ScottPlot.Plot
218     ScottPlot.Plottable.SignalPlotBase<T>
173     ScottPlot.Plottable.ScatterPlot
139     ScottPlot.Settings
120     ScottPlot.Ticks.TickCollection
118     ScottPlot.Renderable.Axis
114     ScottPlot.Drawing.Colormap
113     ScottPlot.Control.ControlBackEnd
109     ScottPlot.DataGen
99      ScottPlot.Plottable.AxisLineVector
98      ScottPlot.Plottable.Heatmap
95      ScottPlot.Tools
93      ScottPlot.Plottable.RepeatingAxisLine
91      ScottPlot.Plottable.PopulationPlot
85      ScottPlot.Plottable.AxisLine
83      ScottPlot.Plottable.AxisSpan
77      ScottPlot.Plottable.RadialGaugePlot
...
```

### Rank Types by Lines of Code
Similarly, ranking all my project's types by how many lines of code they contain can give me insight into which types may benefit most from refactoring.

```cs
RankTypes("ScottPlot.Metrics.xml", "SourceLines");
```

```txt
Types ranked by SourceLines:
4,155   ScottPlot.Plot
1,182   ScottPlot.DataGen
954     ScottPlot.Plottable.SignalPlotBase<T>
726     ScottPlot.Control.ControlBackEnd
670     ScottPlot.Ticks.TickCollection
670     ScottPlot.Settings
630     ScottPlot.Plottable.ScatterPlot
600     ScottPlot.Renderable.Axis
477     ScottPlot.Statistics.Common
454     ScottPlot.Tools
451     ScottPlot.Plottable.PopulationPlot
432     ScottPlot.Drawing.GDI
343     ScottPlot.Plottable.SignalPlotXYGeneric<TX, TY>
336     ScottPlot.Plottable.RepeatingAxisLine
335     ScottPlot.Drawing.Colormap
332     ScottPlot.Plottable.AxisLineVector
...
```

### Rank Types by Maintainability

The [Maintainability Index](https://learn.microsoft.com/en-us/visualstudio/code-quality/code-metrics-maintainability-index-range-and-meaning) is a value between 0 (worst) and 100 (best) that represents the relative ease of maintaining the code. It's calculated from a combination of [Halstead complexity](https://en.wikipedia.org/wiki/Halstead_complexity_measures) (size of the compiled code), [Cyclomatic complexity](https://en.wikipedia.org/wiki/Cyclomatic_complexity) (number of paths that can be taken through the code), and the total number of lines of code.

```cs
MaintainabilityIndex = 171 
  - 5.2 * Math.Log(HalsteadVolume) 
  - 0.23 * CyclomaticComplexity
  - 16.2 * Math.Log(LinesOfCCode);
```

The maintainability index is calculated by `Microsoft.CodeAnalysis.Metrics` so we don't have to. I don't know how Microsoft arrived at their weights for this formula, but the overall idea is described [here](https://learn.microsoft.com/en-us/visualstudio/code-quality/code-metrics-maintainability-index-range-and-meaning).

```cs
RankTypes("ScottPlot.Metrics.xml", "MaintainabilityIndex", highToLow: false);
```

```txt
43      ScottPlot.Drawing.Tools
48      ScottPlot.Statistics.Interpolation.Cubic
48      ScottPlot.Statistics.Interpolation.PeriodicSpline
49      ScottPlot.Statistics.Interpolation.EndSlopeSpline
49      ScottPlot.Statistics.Interpolation.NaturalSpline
50      ScottPlot.Renderable.AxisTicksRender
54      ScottPlot.Statistics.Interpolation.CatmullRom
55      ScottPlot.Statistics.Interpolation.SplineInterpolator
57      ScottPlot.DataGen
58      ScottPlot.DataStructures.SegmentedTree<T>
58      ScottPlot.MarkerShapes.Hashtag
58      ScottPlot.Ticks.TickCollection
59      ScottPlot.MarkerShapes.Asterisk
59      ScottPlot.Plottable.SignalPlotXYGeneric<TX, TY>
59      ScottPlot.Statistics.Interpolation.Bezier
60      ScottPlot.Statistics.Interpolation.Chaikin
61      ScottPlot.Generate
61      ScottPlot.Plot
61      ScottPlot.Statistics.Finance
...
```

### Create Custom HTML Reports

With a little more effort you can generate HTML reports that use tables and headings to highlight useful code metrics and draw attention to types that could benefit from refactoring to improve maintainability.

* View the sample report: [report.html](report.html)
* Download the code used to generate it: [CodeAnalysisReport.zip](CodeAnalysisReport.zip)

<a href="report.html"><img src="report.png" class="img-fluid d-block my-5 border shadow mx-auto"></a>

## Conclusions

Microsoft's official [Microsoft.CodeAnalysis.Metrics](https://www.nuget.org/packages/Microsoft.CodeAnalysis.Metrics/) NuGet package is a useful tool for analyzing assemblies, navigating through namespaces, types, properties, and methods, and evaluating their metrics. Since these analyses can be performed using console applications, they can be easily integrated into CI pipelines or used to create standalone code analysis applications. Future projects can build on the concepts described here to create graphical visualizations of code metrics in large projects.

## Resources

* [Code metrics values](https://learn.microsoft.com/en-us/visualstudio/code-quality/code-metrics-values) - official documentation of the code metrics analysis system

* [Visual Studio source code analysis](https://learn.microsoft.com/en-us/visualstudio/code-quality/roslyn-analyzers-overview)

* [Microsoft.CodeAnalysis.Metrics NuGet Package](https://www.nuget.org/packages/Microsoft.CodeAnalysis.Metrics/)

* [Code metrics: Maintainability Index](https://learn.microsoft.com/en-us/visualstudio/code-quality/code-metrics-maintainability-index-range-and-meaning)

* [NDepend](https://www.ndepend.com/) is commercial software for performing code analysis on .NET code bases and has many advanced features that make it worth considering for organizations that wish to track code quality and who can afford the cost. The [NDepend Sample Reports](https://www.ndepend.com/sample-reports/) demonstrate useful ways to report code analysis metrics.

* This page documents findings originally discussed in [ScottPlot issue #2454](https://github.com/ScottPlot/ScottPlot/issues/2454)
December 17th, 2022

Divide 10 MHz to 1PPS with a Microcontroller

I often find it useful to gate frequency counters using a 1 pulse per second (1PPS) signal derived from a 10 MHz precision frequency reference. However, a divide-by-10-million circuit isn't trivial to implement. Counter ICs exist which enable divide-by-100 by combining multiple divide-by-2 and divide-by-5 stages (e.g., MC74HC390A around $0.85 each), but dividing 10 MHz all the way down to 1Hz would require at least 4 of these chips and a lot of wiring.

You can clock a microcontroller at 10 MHz and use its timer and interrupt systems to generate 1PPS. For example, an ATTiny202 in an 8-pin SOIC package is available from Mouser (>50k stocked) for $0.51 each. Note that modern series AVRs require a special UDPI programmer.

ATTiny202 ($0.51) ATTint826 ($0.95)

This page documents a divide-by-10-million circuit achieved with a single microcontroller to scale a 10MHz frequency reference down to 1PPS. I'm using an ATTiny826 because that is what I have on hand, but these concepts apply to any microcontroller with a 16-bit timer.

ATTiny Breakout Board

Some AVRs come in DIP packages but their pin numbers may be different than the same chip in a SMT package. To facilitate prototyping using designs and code that will work identically across a breadboard prototype and a PCB containing SMT chips, I prefer to build DIP breakout boards using whatever SMT package I intend to include in my final builds. In this case it's ATTint826 in a SOIC-20 package, and I can easily use this in a breadboard by soldering them onto SOIC-to-DIP breakout boards.

I assembled the breakout board by hand using a regular soldering iron. When working with small packages it helps so much to coat the pins with a little tack flux to facilitate wetting and prevent solder bridges. I'm presently using Chip Quik NC191. Even if flux is advertized as "no-clean", it's good practice and makes the boards look much nicer to remove remaining flux with acetone and Q-tips or brushes.

Circuit

  • FTDI breakout board for power: To test this design I'm using a FT232 breakout board just to provide easy access to GND and Vcc (5V from the USB rail).

  • 10 MHz can oscillator: It's not ovenized or GPS disciplined, but I'm using this as a stand-in for whatever high-precision 10 MHz frequency standard will eventually be used in this circuit. The important thing is just to know that it outputs 0-5V square waves at 10 MHz going into the EXTCLK pin of the microcontroller

  • UPDI Programmer: I'm using the Atmel-ICE, but a MPLAB Snap would also work here. See Programming Modern AVR Microcontrollers for more information.

  • Output: A LED on an output pin will visualize the 1pps signal

Configuration Change Protection (CCP)

Traditional AVR microcontrollers used fuse bits to set the clock source, but modern series chips can change the clock source from within code. However, modifying the clock source requires temporarily disabling the configuration change protection (CCP) system.

Disabling the CCP only lasts four clock cycles, so the immediate next statement must be assignment of the new value. I use the following function to facilitate this action.

/* Write a value to a CCP-protected register */
void ccp_write(volatile register8_t* address, uint8_t value){
    CCP = CCP_IOREG_gc;
    *address = value;
}
// Use internal 20 MHz clock with CKOUT pin enabled
ccp_write(&CLKCTRL.MCLKCTRLA, CLKCTRL.MCLKCTRLA | CLKCTRL_CLKOUT_bm);

Do not use compound statements when writing to the CCP register. The code below fails to change clock as one may expect by looking at the code, presumably because the combined OR operation with the assignment exceeds four clock cycles. Instead of direct assignment, use the ccp_write function described above.

// WARNING: This code does not actually change the clock source
CCP = CCP_IOREG_gc;
CLKCTRL.MCLKCTRLA = CLKCTRL.MCLKCTRLA | CLKCTRL_CLKOUT_bm;

Configuring the Clock Source

Internal 10 MHz clock

This is the configuration I use to achieve a 10 CPU clock using the built-in 20 MHz oscillator.

void configure_clock_internal_10mhz(){
    ccp_write(&CLKCTRL.MCLKCTRLA, CLKCTRL.MCLKCTRLA | CLKCTRL_CLKOUT_bm); // 20 MHz internal clock, enable CKOUT
    ccp_write(&CLKCTRL.MCLKCTRLB, CLKCTRL_PEN_bm); // enable divide-by-2 clock prescaler
}

External 10 MHz clock

This is the configuration I use to clock the CPU from an external 10 MHz clock source applied to the EXTCLK pin.

void configure_clock_external(){
    ccp_write(&CLKCTRL.MCLKCTRLA, CLKCTRL_CLKSEL_EXTCLK_gc | CLKCTRL_CLKOUT_bm); // external clock, enable CKOUT
    ccp_write(&CLKCTRL.MCLKCTRLB, 0); // disable prescaler
}

Configuring the 16-Bit Timer

This is how I configured my ATTiny826's TCA0 16-bit timer to fire an interrupt every 200 ms.

  • Prescale: By enabling a divide-by-64 prescaler, my 10 MHz input becomes 156,250 Hz.

  • Top: By setting the top of my 16-bit counter at 31,250, I achieve exactly 5 overflows per second (once every 200 ms).

  • Interrupt: By enabling an overflow interrupt, I am able to call a function every 200 ms.

void configure_1pps(){
    // 10 MHz system clock with div64 prescaler is 156,250 Hz.
    // Setting a 16-bit timer's top to 31,250 means 5 overflows per second.
    TCA0.SINGLE.INTCTRL = TCA_SINGLE_OVF_bm; // overflow interrupt
    TCA0.SINGLE.CTRLB = TCA_SINGLE_WGMODE_NORMAL_gc; // normal mode
    TCA0.SINGLE.PER = 31249UL; // control timer period by setting timer top
    TCA0.SINGLE.CTRLA |= TCA_SINGLE_CLKSEL_DIV64_gc; // set clock source
    TCA0.SINGLE.CTRLA |= TCA_SINGLE_ENABLE_bm; // start timer
}

Alternatively, multiple timers could be cascaded to achieve a similar effect. Modern AVR series microcontrollers have sections in their datasheet describing considerations for cascading two 16-bit timers to create a single 32-bit timer. Using this strategy one could set the top of the counter to 5 million and arrange an interrupt to toggle an LED, resulting in a 1Hz signal with 50% duty.

Configuring the Interrupt System

This method is called whenever the timer's overflow interrupt is triggered. Since it's called 5 times per second, I just need a global counter to count the number of times it was called, and set an output pin to high on every 5th invocation.

uint8_t overflow_count;

ISR(TCA0_OVF_vect)
{
    overflow_count++;
    if (overflow_count == 5){
        overflow_count = 0;
        PORTB.OUT = PIN1_bm;
    } else {
        PORTB.OUT = 0;
    }

    TCA0.SINGLE.INTFLAGS = TCA_SINGLE_OVF_bm; // indicate interrupt was handled
}

Do not forget to enable global interrupts in your start-up sequence! This is an easy mistake to make, and without calling this function the overflow function will never be invoked.

sei(); // enable global interrupts

Results

We have achieved a light that blinks exactly once per second with roughly the same precision as the 10 MHz frequency reference used to clock the microcontroller. This output signal is ready to use for precision measurement purposes, such as toggling the gate of a discrete frequency counter.

Resources

Markdown source code last modified on December 23rd, 2022
---
Title: Divide 10 MHz to 1PPS with a Microcontroller
Description: How to use a microcontroller to inexpensively scale down a 10 MHz reference clock into a one pulse per second (1pps) signal
Date: 2022-12-17 1:09PM EST
Tags: circuit, microcontroller
---

# Divide 10 MHz to 1PPS with a Microcontroller

**I often find it useful to gate frequency counters using a 1 pulse per second (1PPS) signal derived from a 10 MHz precision frequency reference.** However, a divide-by-10-million circuit isn't trivial to implement. Counter ICs exist which enable divide-by-100 by combining multiple divide-by-2 and divide-by-5 stages (e.g., [MC74HC390A](https://www.onsemi.com/pdf/datasheet/mc74hc390a-d.pdf) around $0.85 each), but dividing 10 MHz all the way down to 1Hz would require at least 4 of these chips and a lot of wiring.

**You can clock a microcontroller at 10 MHz and use its timer and interrupt systems to generate 1PPS.** For example, an [ATTiny202](https://www.mouser.com/datasheet/2/268/ATtiny202_402_AVR_MCU_with_Core_Independent_Periph-1384964.pdf) in an 8-pin SOIC package is available from Mouser (>50k stocked) for $0.51 each. Note that [modern series AVRs require a special UDPI programmer](https://swharden.com/blog/2022-12-09-avr-programming). 

ATTiny202 ($0.51) | ATTint826 ($0.95)
---|---
<img src="ATTINY202-SOIC-8.png">|<img src="ATTINY826-SOIC-20.png">

**This page documents a divide-by-10-million circuit achieved with a single microcontroller to scale a 10MHz frequency reference down to 1PPS.** I'm using an [ATTiny826](https://www.mouser.com/datasheet/2/268/ATtiny424_426_427_824_826_827_DataSheet_DS40002311-2887739.pdf) because that is what I have on hand, but these concepts apply to any microcontroller with a 16-bit timer.

![](1pps-breadboard2.jpg)

## ATTiny Breakout Board

**Some AVRs come in DIP packages but their pin numbers may be different than the same chip in a SMT package.** To facilitate prototyping using designs and code that will work identically across a breadboard prototype and a PCB containing SMT chips, I prefer to build DIP breakout boards using whatever SMT package I intend to include in my final builds. In this case it's ATTint826 in a SOIC-20 package, and I can easily use this in a breadboard by soldering them onto [SOIC-to-DIP breakout boards](https://www.amazon.com/s?k=soic+dip+breakout).

![](breakout1.jpg)

**I assembled the breakout board by hand using a regular soldering iron.** When working with small packages it helps _so much_ to coat the pins with a little tack flux to facilitate wetting and prevent solder bridges. I'm presently using [Chip Quik NC191](https://www.amazon.com/s?k=NC191). Even if flux is advertized as "no-clean", it's good practice and makes the boards look much nicer to remove remaining flux with acetone and Q-tips or brushes.

![](breakout2.jpg)
![](breakout3.jpg)

## Circuit

* **FTDI breakout board for power:** To test this design I'm using a FT232 breakout board just to provide easy access to `GND` and `Vcc` (5V from the USB rail).

* **10 MHz can oscillator:** It's not ovenized or GPS disciplined, but I'm using this as a stand-in for whatever high-precision 10 MHz frequency standard will eventually be used in this circuit. The important thing is just to know that it outputs 0-5V square waves at 10 MHz going into the `EXTCLK` pin of the microcontroller

* **UPDI Programmer:** I'm using the Atmel-ICE, but a MPLAB Snap would also work here. See [Programming Modern AVR Microcontrollers](https://swharden.com/blog/2022-12-09-avr-programming) for more information.

* **Output:** A LED on an output pin will visualize the 1pps signal

![](1pps-breadboard.jpg)

## Configuration Change Protection (CCP)

**Traditional AVR microcontrollers used fuse bits to set the clock source, but modern series chips can change the clock source from within code.** However, modifying the clock source requires temporarily disabling the configuration change protection (CCP) system. 

Disabling the CCP only lasts four clock cycles, so the immediate next statement must be assignment of the new value. I use the following function to facilitate this action.

```c
/* Write a value to a CCP-protected register */
void ccp_write(volatile register8_t* address, uint8_t value){
	CCP = CCP_IOREG_gc;
	*address = value;
}
```

```c
// Use internal 20 MHz clock with CKOUT pin enabled
ccp_write(&CLKCTRL.MCLKCTRLA, CLKCTRL.MCLKCTRLA | CLKCTRL_CLKOUT_bm);
```

**Do not use compound statements when writing to the CCP register.**  The code below fails to change clock as one may expect by looking at the code, presumably because the combined OR operation with the assignment exceeds four clock cycles. Instead of direct assignment, use the `ccp_write` function described above.

```c
// WARNING: This code does not actually change the clock source
CCP = CCP_IOREG_gc;
CLKCTRL.MCLKCTRLA = CLKCTRL.MCLKCTRLA | CLKCTRL_CLKOUT_bm;
```

## Configuring the Clock Source


### Internal 10 MHz clock

This is the configuration I use to achieve a 10 CPU clock using the built-in 20 MHz oscillator.

```c
void configure_clock_internal_10mhz(){
	ccp_write(&CLKCTRL.MCLKCTRLA, CLKCTRL.MCLKCTRLA | CLKCTRL_CLKOUT_bm); // 20 MHz internal clock, enable CKOUT
	ccp_write(&CLKCTRL.MCLKCTRLB, CLKCTRL_PEN_bm); // enable divide-by-2 clock prescaler
}
```

### External 10 MHz clock

This is the configuration I use to clock the CPU from an external 10 MHz clock source applied to the `EXTCLK` pin.

```c
void configure_clock_external(){
	ccp_write(&CLKCTRL.MCLKCTRLA, CLKCTRL_CLKSEL_EXTCLK_gc | CLKCTRL_CLKOUT_bm); // external clock, enable CKOUT
	ccp_write(&CLKCTRL.MCLKCTRLB, 0); // disable prescaler
}
```

## Configuring the 16-Bit Timer

This is how I configured my ATTiny826's TCA0 16-bit timer to fire an interrupt every 200 ms.

* **Prescale:** By enabling a divide-by-64 prescaler, my 10 MHz input becomes 156,250 Hz.

* **Top:** By setting the top of my 16-bit counter at 31,250, I achieve exactly 5 overflows per second (once every 200 ms).

* **Interrupt:** By enabling an overflow interrupt, I am able to call a function every 200 ms.

```c
void configure_1pps(){
	// 10 MHz system clock with div64 prescaler is 156,250 Hz.
	// Setting a 16-bit timer's top to 31,250 means 5 overflows per second.
	TCA0.SINGLE.INTCTRL = TCA_SINGLE_OVF_bm; // overflow interrupt
	TCA0.SINGLE.CTRLB = TCA_SINGLE_WGMODE_NORMAL_gc; // normal mode
	TCA0.SINGLE.PER = 31249UL; // control timer period by setting timer top
	TCA0.SINGLE.CTRLA |= TCA_SINGLE_CLKSEL_DIV64_gc; // set clock source
	TCA0.SINGLE.CTRLA |= TCA_SINGLE_ENABLE_bm; // start timer
}
```

**Alternatively, multiple timers could be cascaded to achieve a similar effect.** Modern AVR series microcontrollers have sections in their datasheet describing considerations for cascading two 16-bit timers to create a single 32-bit timer. Using this strategy one could set the top of the counter to 5 million and arrange an interrupt to toggle an LED, resulting in a 1Hz signal with 50% duty.

## Configuring the Interrupt System

**This method is called whenever the timer's overflow interrupt is triggered.** Since it's called 5 times per second, I just need a global counter to count the number of times it was called, and set an output pin to high on every 5th invocation.

```c
uint8_t overflow_count;

ISR(TCA0_OVF_vect)
{
	overflow_count++;
	if (overflow_count == 5){
		overflow_count = 0;
		PORTB.OUT = PIN1_bm;
    } else {
		PORTB.OUT = 0;
	}
    
	TCA0.SINGLE.INTFLAGS = TCA_SINGLE_OVF_bm; // indicate interrupt was handled
}
```

**Do not forget to enable global interrupts in your start-up sequence!** This is an easy mistake to make, and without calling this function the overflow function will never be invoked.

```c
sei(); // enable global interrupts
```

## Results

**We have achieved a light that blinks exactly once per second** with roughly the same precision as the 10 MHz frequency reference used to clock the microcontroller. This output signal is ready to use for precision measurement purposes, such as toggling the gate of a discrete frequency counter.

<video playsinline autoplay muted loop class="border border-dark shadow-sm img-fluid">
  <source src="1pps.webm" type="video/webm">
</video>

## Resources

* Full source code: [ATTiny826 1pps project on GitHub](https://github.com/swharden/AVR-projects/tree/master/ATTiny826%20Timer%201pps) and specifically [main.c](https://github.com/swharden/AVR-projects/blob/master/ATTiny826%20Timer%201pps/ATTiny826%20Clock%20and%20Timer/main.c)

* Inspecting the header file `iotn826.h` in my Program Files / Atmel folder was very useful for identifying named bit masks stored as enums. There is a similarly named file for every supported AVR microcontroller.

* EEVblog forum: [Divide by 10000000](https://www.eevblog.com/forum/projects/divide-by-10000000/)

* EEVblog forum: [Divide by 10 prescaler for frequency counter](https://www.eevblog.com/forum/rf-microwave/divide-by-10-prescaler-for-frequency-counter/)

* EEVblog forum: [10MHz to 1pps divider](https://www.eevblog.com/forum/projects/10mhz-to-1pps-divider/)

* EEVblog forum: [Easiest way to divide 10MHz to 1MHz?](https://www.eevblog.com/forum/projects/easiest-way-to-divide-10mhz-to-1mhz/)

* YouTube: [Build a DIY Frequency Divider](https://www.youtube.com/watch?v=GlKWexGWoXw)

* [picDIV: Single Chip Frequency Divider](http://www.leapsecond.com/pic/picdiv.htm) (2011)

* [PICDIV on GitHub](https://github.com/aewallin/PICDIV)

* All About Circuits thread: [How to convert 10 MHz sine wave to 1Hz TTL (PPS)?](https://forum.allaboutcircuits.com/threads/convert-10-mhz-sine-wave-to-1hz-ttl-pps.54085/)

* [10 MHz to 1 Hz frequency divider using discrete 74HC4017D stages](http://www.perdrix.co.uk/FrequencyDivider/) by David C. Partridge
December 9th, 2022

Programming Modern AVR Microcontrollers

This page describes how to program Microchip's newest series of AVR microcontrollers using official programming gear and software. I spent many years programming the traditional series of Atmel chips, but now several years after Microchip acquired Atmel I am interested in exploring the capabilities of the latest series of AVR microcontrollers (especially the new AVR DD family). Currently the global chip shortage makes it difficult to source traditional ATMega and STM32 chips, but the newest series of AVR microcontrollers feature an impressive set of peripherals for the price and are available from all the major vendors.

TLDR

  • Older AVR microcontrollers are programmed using in-circuit serial programming (ICSP) through the RESET, SCK, MISO, and MOSI pins using cheap programmers like USBtiny. However, serial programming is not supported on newer AVR microcontrollers.

  • New AVR microcontrollers are programmed using the unified program and debug interface (UDPI) exclusively through the UDPI pin. UDPI is a Microchip proprietary interface requiring a UDPI-capable programmer.

  • Official UDPI programmers include Atmel-ICE ($129) and MPLAB Snap ($35). The Atmel-ICE is expensive but it is very well supported. The MPLAB Snap is hacky, requires re-flashing, and has a physical design flaw requiring a hardware modification before it can program AVR series chips.

  • There are notable attempts to create alternative programmers (e.g., jtag2updi and pymcuprog), but this journey into the land of unofficial programmer designs is fraught with abandoned GitHub repositories and a lot of added complexity and brittleness (e.g., SpenceKonde/AVR-Guidance), so to save yourself frustration in the future I highly recommend just buying an officially supported programmer. It's also nice when you can program and debug your microcontroller from within your IDE.

  • UDPI programmers have a Vcc pin that is used to sense supply voltage (but not provide it), so you must power your board yourself while using one of these new programmers.

Blinking a LED is the "Hello, World" of microcontroller programming. Let's take a look at the code necessary to blink a LED on pin 2 of an ATTiny286. It is compiled and programmed onto the chip using Microchip Studio.

#define F_CPU 3333333UL
#include <avr/io.h>
#include <util/delay.h>

int main(void)
{
    PORTA.DIR = 0xFF;
    while (1)
    {
        PORTA.OUT = 255;
        _delay_ms(500);
        PORTA.OUT = 0;
        _delay_ms(500);
    }
}
  • PORTA.DIR sets the direction of pins on port A (0xFF means all outputs)
  • PORTA.OUT sets output voltage on pins of port A (0xFF means all high)
  • Using _delay_ms() requires including delay.h
  • Including delay.h requires defining F_CPU (the CPU frequency)
  • The ATTiny286 datasheet section 11.3.3 indicates the default clock is 20 MHz with a /6 prescaler, so the default clock is 3333333 Hz (3.3 MHz). This behavior can be customized using the Oscillator Configuration Fuse (FUSE.OSCCFG).

ATTiny826 Pinout

From page 14 of the ATTiny826 datasheet

SMT ATTiny Breakout Board

Many of the newer AVR series microcontrollers are not available in breadboard-friendly DIP packages. I find SOIC-to-DIP breakout boards (available on Amazon and eBay) to be useful for experimenting with chips in SOIC packages. Here I added extra power and PA4 (pin 2) LEDs and 10 kΩ current limiting resistors.

I power the device from the 3.3V or 5V pins on a FT232 USB breakout board. Although the topic is out of scope for this article, I find it convenient to use FTDI chips to exchange small amounts of data or debug messages between a microcontroller and a modern PC over USB without requiring special drivers.

Why is programming modern AVRs so difficult?

I'm surprised how little information there is online about how to reliably program modern AVR series microcontrollers. In late 2022 there is a surprisingly large amount of "advice" on this topic which leads to dead ends and broken or abandoned projects. After looking into it for a while, here is my opinionated assessment. Mouser and Digikey have links to expensive programmers, and Amazon has links to similar items but reviews are littered with comments like "arrived bricked" and "can not program AVR series chips". DIY options typically involve abandoned (or soon-to-be abandoned?) GitHub repositories, or instructions for Arduino-related programming. I seek to consolidate and distill the most useful information onto this page, and I hope others will find it useful.

Atmel-ICE: Expensive but Effective

After using $5 ICSP programmers for the last decade I almost fell out of my chair when I saw Microchip's recommended entry-level programmer is over $180! Digikey sells a "basic" version without cables for $130, but that still seems crazy to me. Also, $50 for a ribbon cable?

I found a kit on Amazon that sells the programmer with a cable for $126. It was hard for me to press that buy button, but I figured the time I would save by having access to modern and exotic chips during the present global chip shortage would make it worth it. After a couple days of free Prime shipping, it arrived. It was smaller than I thought it would be from the product photos.

The cable that came with the device seemed a bit hacky at first, but I'm happy to have it. The female 2.54 mm socket is easy to insert breadboard jumpers into.

I'm glad this thing is idiot proof. The very first thing I did after unboxing this programmer was hook it up to my power supply rails using reverse polarity. I misread the pin diagram and confused the socket with the connector (they are mirror images of one another). This is an easy mistake to make though, so here's a picture of the correct orientation. Note the location of the tab on the side of the connector.

Atmel ICE Pinout Programming Connection
  • Black: GND
  • Red: Vcc - This line is used to sense power and not deliver it, so you are responsible for externally powering your board.
  • Blue: UPDI pin - Although a pull-up resistor on the UPDI pin is recommended, I did not find it was required to program my chip on the breadboard in this configuration.

The AVR Ice was easy to use with Microchip Studio. My programmer was detected immediately, a window popped-up and walked me through updating the firmware, and my LED was blinking in no time.

MPLAB Snap: Cheap and Convoluted

Did I really need to spend $126 for an AVR programmer? Amazon carries the MPLAB Snap for $34, but lots of reviews say it doesn't work. After easily getting the Atmel-ICE programmer up and running I thought it would be a similarly easy experience setting-up the MPLAB Snap for AVR UPDI programming, but boy was I wrong. Now that I know the steps to get this thing working it's not so bad, but the information here was only gathered after hours of frustration.

Here are the steps you can take to program modern AVR microcontrollers with UPDI using a MPLAB Snap:

Step 1: Setup MPLAB

  • The MPLAB Snap ships with obsolete firmware and must be re-flashed immediately upon receipt.

  • Microchip Studio's firmware upgrade tool does not actually work with the MPLAB Snap. It shows the board with version 0.00 software and it hangs (with several USB disconnect/reconnect sounds) if you try to upgrade it.

  • You can only re-flash the MPLAB Snap using the MPLAB X IDE. Download the 1.10 GB MPLAB setup executable and install the MPLAB IDE software which occupies a cool 9.83 GB.

Step 2: Re-Flash the Programmer

  • In the MPLAB IDE select Tools and select Hardware Tool Emergency Boot Firmware Recovery. At least this tool is helpful. It walks you through how to reset the device and program the latest firmware.

Step 3: Acknowledge Your Programmer is Defective

Defective may be a strong word, but let's just say the hardware was not designed to enable programming AVR chips using UPDI. Microchip Studio will detect the programmer but if you try to program an AVR you'll get a pop-up error message that provides surprisingly little useful information.

Atmel Studio was unable to start your debug session. Please verify device selection, interface settings, target power and connections to the target device. Look in the details section for more information. StatusCode: 131107 ModuleName: TCF (TCF command: Processes:launch failed.) An illegal configuration parameter was used. Debugger command Activate physical failed.

Step 4: Fix Your Programmer

The reason MPLAB Snap cannot program AVR microcontrollers is because the UPDI pin should be pulled high, but the MPLAB Snap comes from the factory with its UPDI pin pulled low with a 4.7 kΩ resistor to ground. You can try to overpower this resistor by adding a low value pull-up resistor to Vcc (1 kΩ worked for me on a breadboard), but the actual fix is to fire-up the soldering iron and remove that tiny surface-mount pull-down resistor labeled R48.

Have your glasses? R48 is here:

These photos were taken after I removed the resistor. I didn't use hot air. I just touched it a for a few seconds with a soldering iron and wiped it off then threw it away.

You don't need a microscope, but I'm glad I had one.

Step 5: Reflect

You can now program AVR microcontrollers using UPDI with your MPLAB Snap! Blink, LED, blink.

Can you believe this is the officially recommended action? According to the official Microchip Engineering Technical Note ETN #36: MPLAB Snap AVR Interface Modification

  • Symptom: Programming and debugging fails with AVR microcontroller devices that use the UPDI/PDI/TPI interfaces. MPLAB SNAP, Assembly #02-10381-R1 requires an external pull-up resistor for AVR microcontroller devices that use these interfaces.

  • Problem: AVR microcontroller devices that use the UPDI/PDI/TPI interfaces require the idle state of inactivity to be at a logic high level. Internally, the AVR devices have a weak (50-100K) pull-up resistor that attempts to keep the line high. An external and stronger pull-up resistor may be enough to mitigate this issue and bring voltages to acceptable VDD levels. In some cases, this may not be enough and the pull-down resistor that is part of the ICSP protocol can be removed for these AVR microcontroller applications.

  • Solution: If most of the applications are AVR-centric, consider removing the R48 resistor as shown below. This completely isolates any loading on the programming data line. Additionally, a pull-up resistor to VDD in the range of 1K to 10K should be used for robustness. Pin 4 of J4 is the TPGD data line used for ICSP interfaces and it also doubles as the DAT signal for UPDI/PDI and TPI interfaces. The pull-up resistor can be mounted directly from TVDD (J4-2) to TPGD/DAT (J4-4). Alternatively, the resistor can be mounted on the application side of the circuit for convenience.

I feel genuinely sorry for the Amazon sellers who are getting poor reviews because they sell this product. It really isn't their fault. I hope Google directs people here so that they can get their boards working and leave positive reviews that point more people to this issue.

UPDI Programming with a Serial Adapter

There is no official support for UPDI programming using a serial adapter, but it seems some people have figured out how to do it in some capacity. There was a promising pyupdi project, but it is now deprecated. At the time of writing the leading project aiming to enable UPDI programming without official hardware is pymcuprog, but its repository has a single commit dated two months ago and no activity since. Interestingly, that commit was made by buildmaster@microchip.com (an unverified email address), so it may not be fair to refer to it as an "unofficial" solution. The long term support of the pymcuprog project remains uncertain, but regardless let's take a closer look at how it works.

To build a programmer you just need a TTL USB serial adapter and a 1kΩ resistor. These are the steps I used to program a LED blink program using this strategy:

  • Use a generic FT232 breakout board to achieve a USB-controlled serial port on my breadboard.

  • Connect the programmer as shown with the RX pin directly to the UPDI pin of the microcontroller and the resistor between the RX and TX pins.

  • Ensure a modern version of Python is installed on your system

  • pip install pymcuprog

  • Use the device manager to identify the name of the COM port representing your programmer. In my case it's COM12.

  • I then interacted with the microcontroller by running pymcuprog from a terminal

Ping the Microcontroller

This command returns the device ID (1E9328 for my ATtiny826) indicating the UPDI connection is working successfully

pymcuprog ping -d attiny826 -t uart -u com12
Connecting to SerialUPDI
Pinging device...
Ping response: 1E9328

Write a Hex File

I used Microchip Studio to compile my C code and generate the hex file. Now I can use pymcuprog to load those hex files onto the chip. It's slower to program and inconvenient to drop to a terminal whenever I want to program a chip, but it works.

pymcuprog write -f LedBlink.hex -d attiny826 -t uart -u com12
Connecting to SerialUPDI
Pinging device...
Ping response: 1E9328
Writing from hex file...
Writing flash...

Conclusions

  • The new AVR series microcontrollers have lots of cool peripherals for the price and are available during a chip shortage that threatens availability of the more common traditional microcontrollers.

  • The Atmel-ICE is expensive, but the most convenient and reliable way to program modern AVR microcontrollers using UPDI.

  • The MPLAB Snap can program modern AVRs using UPDI after a software flash and a hardware modification, but its support for AVRs seems like an afterthought rather than its design priority.

  • You can create a makeshift unofficial UPDI programmer from a USB serial adapter, but the added complexity, lack of debugging capabilities, increased friction during the development loop, and large number of abandoned projects in this space make this an unappealing long term solution in my opinion.

Resources

Markdown source code last modified on December 25th, 2022
---
Title: Programming Modern AVR Microcontrollers
Description: Blink a LED on a modern series AVR using Atmel-ICS or MPLAB Snap UPDI programmers.
Date: 2022-12-09 11:45PM EST
Tags: circuit, microcontroller
---

# Programming Modern AVR Microcontrollers

**This page describes how to program Microchip's newest series of AVR microcontrollers using official programming gear and software.** I spent many years programming the traditional series of Atmel chips, but now several years after Microchip acquired Atmel I am interested in exploring the capabilities of the latest series of AVR microcontrollers (especially the new AVR DD family). Currently the global chip shortage makes it difficult to source traditional ATMega and STM32 chips, but the newest series of AVR microcontrollers feature an impressive set of peripherals for the price and are available from all the major vendors.

<div class="w-75 mx-auto">

![](https://www.youtube.com/embed/M-myqg-2c5s)

</div>

## TLDR

* Older AVR microcontrollers are programmed using _in-circuit serial programming_ (ICSP) through the `RESET`, `SCK`, `MISO`, and `MOSI` pins using cheap programmers like [USBtiny](https://learn.adafruit.com/usbtinyisp). However, serial programming is not supported on newer AVR microcontrollers.

* New AVR microcontrollers are programmed using the _unified program and debug interface_ (UDPI) exclusively through the `UDPI` pin. UDPI is a Microchip proprietary interface requiring a UDPI-capable programmer.

* Official UDPI programmers include [Atmel-ICE](https://www.digikey.com/en/products/detail/microchip-technology/ATATMEL-ICE-BASIC/4753381) ($129) and [MPLAB Snap](https://www.digikey.com/en/products/detail/microchip-technology/PG164100/9562532) ($35). The Atmel-ICE is expensive but it is very well supported. The MPLAB Snap is hacky, requires re-flashing, and has a physical design flaw requiring a hardware modification before it can program AVR series chips.

* There are notable attempts to create alternative programmers (e.g., [jtag2updi](https://github.com/ElTangas/jtag2updi) and [pymcuprog](https://github.com/microchip-pic-avr-tools/pymcuprog)), but this journey into the land of unofficial programmer designs is fraught with abandoned GitHub repositories and a lot of added complexity and brittleness (e.g., [SpenceKonde/AVR-Guidance](https://github.com/SpenceKonde/AVR-Guidance/blob/master/UPDI/jtag2updi.md)), so to save yourself frustration in the future I highly recommend just buying an officially supported programmer. It's also nice when you can program and debug your microcontroller from within your IDE.

* UDPI programmers have a `Vcc` pin that is used to _sense_ supply voltage (but not provide it), so you must power your board yourself while using one of these new programmers.

## ATTiny826 LED Blink

**Blinking a LED is the "Hello, World" of microcontroller programming.** Let's take a look at the code necessary to blink a LED on pin 2 of an [ATTiny286](https://ww1.microchip.com/downloads/en/DeviceDoc/ATtiny424-426-427-824-826-827-DataSheet-DS40002311A.pdf). It is compiled and programmed onto the chip using [Microchip Studio](https://www.microchip.com/en-us/tools-resources/develop/microchip-studio).

```c
#define F_CPU 3333333UL
#include <avr/io.h>
#include <util/delay.h>

int main(void)
{
	PORTA.DIR = 0xFF;
	while (1)
	{
		PORTA.OUT = 255;
		_delay_ms(500);
		PORTA.OUT = 0;
		_delay_ms(500);
	}
}
```

* `PORTA.DIR` sets the direction of pins on port A (`0xFF` means all outputs)
* `PORTA.OUT` sets output voltage on pins of port A (`0xFF` means all high)
* Using `_delay_ms()` requires including `delay.h`
* Including `delay.h` requires defining `F_CPU` (the CPU frequency)
* The [ATTiny286 datasheet section 11.3.3](https://ww1.microchip.com/downloads/en/DeviceDoc/ATtiny424-426-427-824-826-827-DataSheet-DS40002311A.pdf) indicates the default clock is 20 MHz with a /6 prescaler, so the default clock is `3333333 Hz` (3.3 MHz). This behavior can be customized using the Oscillator Configuration Fuse (FUSE.OSCCFG).

## ATTiny826 Pinout

From page 14 of the [ATTiny826 datasheet](https://ww1.microchip.com/downloads/en/DeviceDoc/ATtiny424-426-427-824-826-827-DataSheet-DS40002311A.pdf)

<img src="attiny826-pinout.png" class="img-fluid mx-auto d-block w-75" />

## SMT ATTiny Breakout Board

**Many of the newer AVR series microcontrollers are not available in breadboard-friendly DIP packages.** I find SOIC-to-DIP breakout boards (available on Amazon and eBay) to be useful for experimenting with chips in SOIC packages. Here I added extra power and PA4 (pin 2) LEDs and 10 kΩ current limiting resistors.

<a href="photos/leds2.jpg">
<img src="photos/leds2.jpg" class="img-fluid border shadow my-4" />
</a>

<a href="photos/scope1.jpg">
<img src="photos/scope1.jpg" class="img-fluid border shadow my-4" />
</a>

**I power the device from the 3.3V or 5V pins on a FT232 USB breakout board.** Although the topic is out of scope for this article, I find it convenient to use FTDI chips to exchange small amounts of data or debug messages between a microcontroller and a modern PC over USB without requiring special drivers.

<img src="ft232-breadboard.jpg" class="img-fluid mx-auto d-block w-50" />

## Why is programming modern AVRs so difficult?

**I'm surprised how little information there is online about how to _reliably_ program modern AVR series microcontrollers.** In late 2022 there is a surprisingly large amount of "advice" on this topic which leads to dead ends and broken or abandoned projects. After looking into it for a while, here is my opinionated assessment. Mouser and Digikey have links to expensive programmers, and Amazon has links to similar items but reviews are littered with comments like "arrived bricked" and "can not program AVR series chips". DIY options typically involve abandoned (or soon-to-be abandoned?) GitHub repositories, or instructions for Arduino-related programming. I seek to consolidate and distill the most useful information onto this page, and I hope others will find it useful.

## Atmel-ICE: Expensive but Effective

**After using $5 ICSP programmers for the last decade I almost fell out of my chair when I saw Microchip's recommended entry-level programmer is over $180!** Digikey sells a "basic" version without cables for $130, but that still seems crazy to me. Also, $50 for a ribbon cable?

<a href="avr-ice.webp">
<img src="avr-ice.webp" class="img-fluid w-50 d-block mx-auto my-5" />
</a>

**I found a kit on Amazon that sells the programmer with a cable for $126.** It was hard for me to press that buy button, but I figured the time I would save by having access to modern and exotic chips during the present global chip shortage would make it worth it. After a couple days of free Prime shipping, it arrived. It was smaller than I thought it would be from the product photos.

<a href="photos/atmel-ice-1.jpg">
<img src="photos/atmel-ice-1.jpg" class="img-fluid border shadow my-4" />
</a>

**The cable that came with the device seemed a bit hacky at first, but I'm happy to have it.** The female 2.54 mm socket is easy to insert breadboard jumpers into.

<a href="photos/atmel-ice-2.jpg">
<img src="photos/atmel-ice-2.jpg" class="img-fluid border shadow my-4" />
</a>

**I'm glad this thing is idiot proof.** The very first thing I did after unboxing this programmer was hook it up to my power supply rails using reverse polarity. I misread the pin diagram and confused the _socket_ with the _connector_ (they are mirror images of one another). This is an easy mistake to make though, so here's a picture of the correct orientation. Note the location of the tab on the side of the connector.

Atmel ICE Pinout | Programming Connection
---|---
<a href="atmel-ice-pinout.png"><img src="atmel-ice-pinout.png" class="img-fluid"></a>|<a href="photos/atmel-ice-3.jpg"><img src="photos/atmel-ice-3.jpg" class="img-fluid"></a>

* Black: `GND`
* Red: `Vcc` - This line is used to _sense_ power and not _deliver_ it, so you are responsible for externally powering your board.
* Blue: `UPDI` pin - Although a pull-up resistor on the UPDI pin is recommended, I did not find it was required to program my chip on the breadboard in this configuration.

**The AVR Ice was easy to use with Microchip Studio.** My programmer was detected immediately, a window popped-up and walked me through updating the firmware, and my LED was blinking in no time.

<a href="photos/atmel-ice-4.jpg">
<img src="photos/atmel-ice-4.jpg" class="img-fluid border shadow my-4" />
</a>

## MPLAB Snap: Cheap and Convoluted

**Did I really need to spend $126 for an AVR programmer? Amazon carries the MPLAB Snap for $34, but lots of reviews say it doesn't work.** After easily getting the Atmel-ICE programmer up and running I thought it would be a similarly easy experience setting-up the MPLAB Snap for AVR UPDI programming, but boy was I wrong. Now that I know the steps to get this thing working it's not so bad, but the information here was only gathered after hours of frustration. 

<a href="mplab-snap.webp">
<img src="mplab-snap.webp" class="img-fluid d-block mx-auto w-75" />
</a>

<a href="photos/mplab-snap-1.jpg">
<img src="photos/mplab-snap-1.jpg" class="img-fluid border shadow my-4" />
</a>

Here are the steps you can take to program modern AVR microcontrollers with UPDI using a MPLAB Snap:

### Step 1: Setup MPLAB

* The MPLAB Snap ships with obsolete firmware and must be re-flashed immediately upon receipt.

* Microchip Studio's firmware upgrade tool does not actually work with the MPLAB Snap. It shows the board with version 0.00 software and it hangs (with several USB disconnect/reconnect sounds) if you try to upgrade it.

* You can only re-flash the MPLAB Snap using the MPLAB X IDE. Download the 1.10 GB [MPLAB setup](https://www.microchip.com/en-us/tools-resources/develop/mplab-x-ide) executable and install the MPLAB IDE software which occupies a cool 9.83 GB.

### Step 2: Re-Flash the Programmer

* In the MPLAB IDE select `Tools` and select `Hardware Tool Emergency Boot Firmware Recovery`. At least this tool is helpful. It walks you through how to reset the device and program the latest firmware.

### Step 3: Acknowledge Your Programmer is Defective

Defective may be a strong word, but let's just say the hardware was not designed to enable programming AVR chips using UPDI. Microchip Studio will detect the programmer but if you try to program an AVR you'll get a pop-up error message that provides surprisingly little useful information.

<img src="verify.png" class="mx-auto d-block img-fluid" />

> Atmel Studio was unable to start your debug session. Please verify device selection, interface settings, target power and connections to the target device. Look in the details section for more information.
> StatusCode:	131107
> ModuleName:	TCF (TCF command: Processes:launch failed.)
> An illegal configuration parameter was used. Debugger command Activate physical failed.

### Step 4: Fix Your Programmer

**The reason MPLAB Snap cannot program AVR microcontrollers is because the UPDI pin should be pulled _high_, but the MPLAB Snap comes from the factory with its UPDI pin pulled _low_ with a 4.7 kΩ resistor to ground.** You can try to overpower this resistor by adding a low value pull-up resistor to Vcc (1 kΩ worked for me on a breadboard), but the actual fix is to fire-up the soldering iron and remove that tiny surface-mount pull-down resistor labeled `R48`.

Have your glasses? R48 is here:

<a href="photos/mplab-snap-fix.jpg">
<img src="photos/mplab-snap-fix.jpg" class="img-fluid border shadow my-4" />
</a>


**These photos were taken after I removed the resistor.** I didn't use hot air. I just touched it a for a few seconds with a soldering iron and wiped it off then threw it away.

<a href="photos/scope2.jpg">
<img src="photos/scope2.jpg" class="img-fluid border shadow my-4" />
</a>

You don't need a microscope, but I'm glad I had one.

### Step 5: Reflect

You can now program AVR microcontrollers using UPDI with your MPLAB Snap! Blink, LED, blink.

<a href="photos/mplab-snap-2.jpg">
<img src="photos/mplab-snap-2.jpg" class="img-fluid border shadow my-4" />
</a>

**Can you believe this is the officially recommended action?** According to the official Microchip Engineering Technical Note [ETN #36](http://ww1.microchip.com/downloads/en/DeviceDoc/ETN36_MPLAB%20Snap%20AVR%20Interface%20Modification.pdf): MPLAB Snap AVR Interface Modification

* **Symptom:** Programming and debugging fails with AVR microcontroller devices that use the UPDI/PDI/TPI interfaces. MPLAB SNAP, Assembly #02-10381-R1 requires an external pull-up resistor for AVR microcontroller
devices that use these interfaces.

* **Problem:** AVR microcontroller devices that use the UPDI/PDI/TPI interfaces require the idle state of inactivity to be at a logic high level. Internally, the AVR devices have a weak (50-100K) pull-up resistor that attempts to keep the line high. An external and stronger pull-up resistor may be enough to mitigate this issue and bring voltages to acceptable VDD levels. In some cases, this may not be enough and the pull-down resistor that is part of the ICSP protocol can be removed for these AVR microcontroller applications.

* **Solution:** If most of the applications are AVR-centric, consider removing the R48 resistor as shown below. This completely isolates any loading on the programming data line. Additionally, a pull-up resistor to VDD in the range of 1K to 10K should be used for robustness. Pin 4 of J4 is the TPGD data line used for ICSP interfaces and it also doubles as the DAT signal for UPDI/PDI and TPI interfaces. The pull-up resistor can be mounted directly from TVDD (J4-2) to TPGD/DAT (J4-4). Alternatively, the resistor can be mounted on the application side of the circuit
for convenience.

**I feel genuinely sorry for the Amazon sellers who are getting poor reviews because they sell this product.** It really isn't their fault. I hope Google directs people here so that they can get their boards working and leave positive reviews that point more people to this issue.

## UPDI Programming with a Serial Adapter

There is no official support for UPDI programming using a serial adapter, but it seems some people have figured out how to do it in some capacity. There was a promising [pyupdi](https://github.com/mraardvark/pyupdi) project, but it is now deprecated. At the time of writing the leading project aiming to enable UPDI programming without official hardware is [pymcuprog](https://github.com/microchip-pic-avr-tools/pymcuprog), but its repository has a single commit dated two months ago and no activity since. Interestingly, [that commit](https://github.com/microchip-pic-avr-tools/pymcuprog/commit/593afdc8e089e39a4fed9f4fb19ae81f5f51e9a5.patch) was made by buildmaster@microchip.com (an unverified email address), so it may not be fair to refer to it as an "unofficial" solution. The long term support of the pymcuprog project remains uncertain, but regardless let's take a closer look at how it works.

![](updi-ftdi-serial-programmer.png)

To build a programmer you just need a TTL USB serial adapter and a 1kΩ resistor. These are the steps I used to program a LED blink program using this strategy:

* Use a generic [FT232 breakout board](https://www.amazon.com/s?k=ft232+breakout) to achieve a USB-controlled serial port on my breadboard.

* Connect the programmer as shown with the RX pin directly to the UPDI pin of the microcontroller and the resistor between the RX and TX pins.

* Ensure a [modern version of Python](https://www.python.org/) is installed on your system

* `pip install pymcuprog`

* Use the device manager to identify the name of the COM port representing your programmer. In my case it's `COM12`.

* I then interacted with the microcontroller by running `pymcuprog` from a terminal

### Ping the Microcontroller

This command returns the device ID (1E9328 for my ATtiny826) indicating the UPDI connection is working successfully

```bash
pymcuprog ping -d attiny826 -t uart -u com12
```

```
Connecting to SerialUPDI
Pinging device...
Ping response: 1E9328
```

### Write a Hex File

I used Microchip Studio to compile my C code and generate the hex file. Now I can use `pymcuprog` to load those hex files onto the chip. It's slower to program and inconvenient to drop to a terminal whenever I want to program a chip, but it works.

```
pymcuprog write -f LedBlink.hex -d attiny826 -t uart -u com12
```

```
Connecting to SerialUPDI
Pinging device...
Ping response: 1E9328
Writing from hex file...
Writing flash...
```

## Conclusions

* The new AVR series microcontrollers have lots of cool peripherals for the price and are available during a chip shortage that threatens availability of the more common traditional microcontrollers.

* The Atmel-ICE is expensive, but the most convenient and reliable way to program modern AVR microcontrollers using UPDI.

* The MPLAB Snap can program modern AVRs using UPDI after a software flash and a hardware modification, but its support for AVRs seems like an afterthought rather than its design priority.

* You can create a makeshift unofficial UPDI programmer from a USB serial adapter, but the added complexity, lack of debugging capabilities, increased friction during the development loop, and large number of abandoned projects in this space make this an unappealing long term solution in my opinion.

## Resources

* Atmel-ICE
  * [Atmel-ICE on Mouser](https://www.mouser.com/ProductDetail/Microchip-Technology-Atmel/ATATMEL-ICE?qs=sGAEpiMZZMuRZxwUfDU0miN4udwF8GpUanrVt%252BDSn9Q4SZQ5wSGB4Q%3D%3D) (currently $180.64)
  * [Atmel-ICE on DigiKey](https://www.digikey.com/en/products/detail/microchip-technology/ATATMEL-ICE/4753379) (currently $180.62)
  * [Atmel-ICE on Amazon](https://www.amazon.com/s?k=atmel+ice) (currently $126.49)
  * [Atmel-ICE on eBay](https://www.ebay.com/sch/i.html?_nkw=atmel-ice) (currently $135.00)
  * [Atmel-ICE datasheet](https://ww1.microchip.com/downloads/en/DeviceDoc/Atmel-ICE_UserGuide.pdf)
* MPLAB Snap
  * [MPLAB Snap on Mouser](https://www.mouser.com/ProductDetail/Microchip-Technology-Atmel/PG164100?qs=w%2Fv1CP2dgqoaLDDBjfzhMQ%3D%3D) (currently $34.77)
  * [MPLAB Snap on DigiKey](https://www.digikey.com/en/products/detail/microchip-technology/PG164100/9562532) (currently $34.76)
  * [MPLAB Snap on Amazon](https://www.amazon.com/s?k=mplab+snap) (currently $34.09)
  * [MPLAB Snap datasheet](https://ww1.microchip.com/downloads/en/DeviceDoc/50002787C.pdf)
  * [MPLAB Snap AVR UPDI modification](http://ww1.microchip.com/downloads/en/DeviceDoc/ETN36_MPLAB%20Snap%20AVR%20Interface%20Modification.pdf)
* [ATTiny826 datasheet](https://ww1.microchip.com/downloads/en/DeviceDoc/ATtiny424-426-427-824-826-827-DataSheet-DS40002311A.pdf)
* [UPDI Physical Interface](https://onlinedocs.microchip.com/pr/GUID-DDB0017E-84E3-4E77-AAE9-7AC4290E5E8B-en-US-4/index.html)
* [Contact me](https://swharden.com/about/) if you have suggestions or updated information
November 15th, 2022

Interfacing HX710 Differential ADC with Arduino

This page demonstrates how to read differential voltage from a HX710 ADC using Arduino. I recently obtained some pressure sensor boards from Amazon for less than $3 each under names like 6pcs 3.3-5V Digital Barometric Air Pressure Sensor Module Liquid Water Level Controller Board 0-40KPa that use this ADC. Several years ago I worked on a precision pressure meter project based on an I2C temperature and pressure sensor (MS5611), and now that I see new inexpensive SPI pressure sensor modules on the consumer market I'm interested to learn more about their capabilities.

Analog-to-Digital Converter IC

The ADC chip is easily identified as a HX710B 24-Bit Analog-to-Digital Converter (ADC) with Built-in Temperature Sensor. According to the datasheet it can be powered by a 3.3V or 5V supply, and the value it reports is the differential voltage between two input pins.

The datasheet indicates this device can be run from a 3.3V or 5V supply, it uses a built-in fixed-gain (128x) differential amplifier, and it can read up to 40 samples per second. The datasheet provides an example circuit demonstrating how this ADC can be used to measure weight from a scale sensor:

Pressure Sensor

To get a better idea of how this sensor works it would be helpful to locate its product number. I had a hunch it was beneath the part so I desoldered it, and indeed I found part identification information.

The pressure sensor is labeled as a PSG010S but unfortunately I struggled to find a quality datasheet for it. I did find some now-deleted images from an AliExpress listing showing the differences between the base model and the R and S variants. I found this PSG010R datasheet (curiously written in Comic Sans) indicating that maximum voltage is 5V and that the gauge pressure is 0 - 40KPa (0 - 5.8 PSI). This seems to be a fairly standard differential pressure sensor design using a pair of voltage dividers where the pressure is a function of the difference in voltage at the two mid-points (a Wheatstone bridge).

Update (2022-12-23): I received an email from somebody offering additional information about this component:

The PSG010 reports positive and negative pressures and can easily have its range shifted to almost double in one direction with almost none in the other. All that is needed is to lift the +V (2) or ground pin (5) and insert a surface mount 75R ±15R under it. Lifting the ground side by 75R makes it double positive, while pushing the applied +V down makes it double negative (vacuum).
-- bruceg

Read HX710B with Arduino

This code demonstrates how to measure HX710B values using Arduino and display the readings in the serial terminal sufficient to graph in real time using the serial plotter. The animated plot is what it looks like when I blow puffs of air on the sensor.

const int HX_OUT_PIN = 2;
const int HX_SCK_PIN = 3;

enum HX_MODE { NONE, DIFF_10Hz, TEMP_40Hz, DIFF_40Hz};
const byte HX_MODE = DIFF_40Hz;

void setup() {
  pinMode(HX_SCK_PIN, OUTPUT);
  pinMode(HX_OUT_PIN, INPUT);
  Serial.begin(9600);
}

void loop() {
  Serial.println(readHX());
}

unsigned long readHX() {

  // pulse clock line to start a reading
  for (char i = 0; i < HX_MODE; i++) {
    digitalWrite(HX_SCK_PIN, HIGH);
    digitalWrite(HX_SCK_PIN, LOW);
  }

  // wait for the reading to finish
  while (digitalRead(HX_OUT_PIN)) {}

  // read the 24-bit pressure as 3 bytes using SPI
  byte data[3];
  for (byte j = 3; j--;) {
    data[j] = shiftIn(HX_OUT_PIN, HX_SCK_PIN, MSBFIRST);
  }

  data[2] ^= 0x80;  // see note

  // shift the 3 bytes into a large integer
  long result;
  result += (long)data[2] << 16;
  result += (long)data[1] << 8;
  result += (long)data[0];

  return result;
}

Note: This code flips the most significant bit of the sensor reading. The sensor always returns this bit as 1, except for the case of an out-of-range error (see excerpt from datasheet below). By simply flipping the bit our reported values are a continuous range from 0 to 2^14-1, with the edge values representing out-of-range errors.

The output 24 bits of data is in 2’s complement format. When input differential signal goes out of the 24 bit range, the output data will be saturated at 0x800000 (MIN) or 0x7FFFFF (MAX) until the input signal comes back to the input range.
-- HX710 datasheet

Update (2022-12-23): I received an email from someone offering feedback about this code:

This code works in a loop, but perhaps by accident. The strongly worded statements in the HX710 datasheet about 25 - 27 clocks per readout imply that it is risky to rely on this. It may be that hanging clocks induce unwanted sleep modes or over-run into the next read cycle, etc. There is simply no real explanation in what is shown, so best to be safe - always set the next mode immediately AFTER collecting a reading and then always poll for new data ready before attempting a collection. Your 'pulse clock line to start a reading' loop before a reading should be 'add next mode' after a reading to comply with the timing specification. This will ensure that the next conversion will be available rather than the next scheduled conversion AFTER the mode is eventually sent.
-- bruceg

Open-Source HX710B Libraries

Although some libraries are available which facilitate interacting with the HX710, here I engage with it discretely to convey each step of the conversion and measurement process. I found that many libraries use the 10 Hz mode by default, whereas I certainly prefer the 40 Hz mode. More frustratingly, code in many libraries refer to this as gain, which is incorrect. The datasheet indicates gain is fixed at 128 and cannot be changed in software.

Update (2022-12-23): I received an email explaining why people often use "gain" and "mode" when referring to the HX710:

The HX711 is similar to the HX710 but it has user selectable gain AND user selectable sample rates BUT only certain combinations are allowed, so setting mode WILL also select its matched gain value. The HX710 uses most of the same internals, but with just 3 modes - reading the Wheatstone Bridge always using 128 gain at 10 or 40Hz while swapping to Avolt (HX710A) or internal Temperature (HX710B) uses a lower gain and less digits. So for people familiar with the HX711 there is no ambiguity in mixing mode and gain.
-- bruceg

Resources

Markdown source code last modified on December 24th, 2022
---
Title: Interfacing HX710 Differential ADC with Arduino
Description: How to read differential voltage from a HX710 ADC using Arduino
Date: 2022-11-15 12:30AM EST
Tags: circuit, microcontroller
---

# Interfacing HX710 Differential ADC with Arduino

**This page demonstrates how to read differential voltage from a HX710 ADC using Arduino.** I recently obtained some pressure sensor boards from Amazon for less than $3 each under names like _6pcs 3.3-5V Digital Barometric Air Pressure Sensor Module Liquid Water Level Controller Board 0-40KPa_ that use this ADC. Several years ago I worked on a [precision pressure meter project](https://swharden.com/blog/2017-04-29-precision-pressure-meter-project/) based on an [I2C](https://en.wikipedia.org/wiki/I%C2%B2C)  temperature and pressure sensor ([MS5611](https://www.te.com/commerce/DocumentDelivery/DDEController?Action=showdoc&DocId=Data+Sheet%7FMS5611-01BA03%7FB3%7Fpdf%7FEnglish%7FENG_DS_MS5611-01BA03_B3.pdf%7FCAT-BLPS0036)), and now that I see new inexpensive [SPI](https://en.wikipedia.org/wiki/Serial_Peripheral_Interface) pressure sensor modules on the consumer market I'm interested to learn more about their capabilities.

<img src="hx710b-pressure-board.jpg" class="my-5 border border-dark shadow img-fluid w-75 mx-auto d-block">

## Analog-to-Digital Converter IC

**The ADC chip is easily identified as a [HX710B](https://www.electronicscomp.com/datasheet/hx710b-ic-datasheet.pdf) _24-Bit Analog-to-Digital Converter (ADC) with Built-in Temperature Sensor_.** According to the datasheet it can be powered by a 3.3V or 5V supply, and the value it reports is the differential voltage between two input pins. 

<img src="hx710b-pinout.jpg" class="my-5 img-fluid w-75 mx-auto d-block">

The datasheet indicates this device can be run from a 3.3V or 5V supply, it uses a built-in fixed-gain (128x) differential amplifier, and it can read up to 40 samples per second. The datasheet provides an example circuit demonstrating how this ADC can be used to measure weight from a scale sensor:

<img src="hx710-datasheet.jpg" class="my-5 img-fluid w-75 mx-auto d-block">

## Pressure Sensor

To get a better idea of how this sensor works it would be helpful to locate its product number. I had a hunch it was beneath the part so I desoldered it, and indeed I found part identification information.

<img src="hx710b-pressure-psg010s.jpg" class="my-5 border border-dark shadow img-fluid w-75 mx-auto d-block">

**The pressure sensor is labeled as a PSG010S** but unfortunately I struggled to find a quality datasheet for it. I did find some now-deleted images from an AliExpress listing showing the differences between the base model and the R and S variants. 
I found [this PSG010R datasheet](https://www.katranji.com/tocimages/files/536845-544144.pdf) (curiously written in Comic Sans) indicating that maximum voltage is 5V and that the gauge pressure is 0 - 40KPa (0 - 5.8 PSI). This seems to be a fairly standard [differential pressure sensor](https://www.avnet.com/wps/portal/abacus/solutions/technologies/sensors/pressure-sensors/measurement-types/differential/) design using a pair of voltage dividers where the pressure is a function of the difference in voltage at the two mid-points (a [Wheatstone bridge](https://en.wikipedia.org/wiki/Wheatstone_bridge)).

**Update (2022-12-23):** I received an email from somebody offering additional information about this component:

> The PSG010 reports positive and negative pressures and can easily have its range shifted to almost double in one direction with almost none in the other.  All that is needed is to lift the +V (2) or ground pin (5) and insert a surface mount 75R ±15R under it. 
Lifting the ground side by 75R makes it double positive, while pushing the applied +V down makes it double negative (vacuum).<br>
> -- <cite class="text-end">bruceg</cite>


<img src="psg-pressure-sensor.jpg" class="my-5 border border-dark shadow img-fluid w-75 mx-auto d-block">

## Read HX710B with Arduino

**This code demonstrates how to measure HX710B values using Arduino** and display the readings in the serial terminal sufficient to graph in real time using the serial plotter. The animated plot is what it looks like when I blow puffs of air on the sensor.

<img src="hx710-arduino-plot.gif" class="my-5 img-fluid mx-auto d-block">

```c
const int HX_OUT_PIN = 2;
const int HX_SCK_PIN = 3;

enum HX_MODE { NONE, DIFF_10Hz, TEMP_40Hz, DIFF_40Hz};
const byte HX_MODE = DIFF_40Hz;

void setup() {
  pinMode(HX_SCK_PIN, OUTPUT);
  pinMode(HX_OUT_PIN, INPUT);
  Serial.begin(9600);
}

void loop() {
  Serial.println(readHX());
}

unsigned long readHX() {

  // pulse clock line to start a reading
  for (char i = 0; i < HX_MODE; i++) {
    digitalWrite(HX_SCK_PIN, HIGH);
    digitalWrite(HX_SCK_PIN, LOW);
  }

  // wait for the reading to finish
  while (digitalRead(HX_OUT_PIN)) {}

  // read the 24-bit pressure as 3 bytes using SPI
  byte data[3];
  for (byte j = 3; j--;) {
    data[j] = shiftIn(HX_OUT_PIN, HX_SCK_PIN, MSBFIRST);
  }
  
  data[2] ^= 0x80;  // see note

  // shift the 3 bytes into a large integer
  long result;
  result += (long)data[2] << 16;
  result += (long)data[1] << 8;
  result += (long)data[0];

  return result;
}
```

**Note: This code flips the most significant bit of the sensor reading.** The sensor always returns this bit as `1`, except for the case of an out-of-range error (see excerpt from datasheet below). By simply flipping the bit our reported values are a continuous range from `0` to `2^14-1`, with the edge values representing out-of-range errors.

> The output 24 bits of data is in [2’s complement format](https://en.wikipedia.org/wiki/Two%27s_complement).
> When input differential signal goes out of the 24 bit range, the output data will be saturated at `0x800000` (MIN) or `0x7FFFFF` (MAX)
> until the input signal comes back to the input range.<br>
> -- <cite class="text-end"><a href='https://www.electronicscomp.com/datasheet/hx710b-ic-datasheet.pdf'>HX710 datasheet</a></cite>

**Update (2022-12-23):** I received an email from someone offering feedback about this code:

> This code works in a loop, but perhaps by accident. The strongly worded statements in the [HX710 datasheet](https://www.electronicscomp.com/datasheet/hx710b-ic-datasheet.pdf) about 25 - 27 clocks per readout imply that it is risky to rely on this.  It may be that hanging clocks induce unwanted sleep modes or over-run into the next read cycle, etc.  There is simply no real explanation in what is shown, so best to be safe - always set the next mode immediately AFTER collecting a reading and then always poll for new data ready before attempting a collection. Your 'pulse clock line to start a reading' loop before a reading should be 'add next mode' after a reading to comply with the timing specification.  This will ensure that the next conversion will be available rather than the next scheduled conversion AFTER the mode is eventually sent.<br>
> -- <cite class="text-end">bruceg</cite>

## Open-Source HX710B Libraries

Although some libraries are available which facilitate interacting with the HX710, here I engage with it discretely to convey each step of the conversion and measurement process. I found that many libraries use the 10 Hz mode by default, whereas I certainly prefer the 40 Hz mode. More frustratingly, code in many libraries refer to this as _gain_, which is incorrect. The datasheet indicates gain is fixed at 128 and cannot be changed in software.

**Update (2022-12-23):** I received an email explaining why people often use "gain" and "mode" when referring to the HX710:

> The [HX711](https://www.digikey.com/htmldatasheets/production/1836471/0/0/1/HX711.pdf) is similar to the [HX710](https://www.electronicscomp.com/datasheet/hx710b-ic-datasheet.pdf) but it has user selectable gain AND user selectable sample rates BUT only certain combinations are allowed, so setting mode WILL also select its matched gain value.
The HX710 uses most of the same internals, but with just 3 modes - reading the Wheatstone Bridge always using 128 gain at 10 or 40Hz while swapping to Avolt (HX710A) or internal Temperature (HX710B) uses a lower gain and less digits. So for people familiar with the HX711 there is no ambiguity in mixing mode and gain.<br>
> -- <cite class="text-end">bruceg</cite>

## Resources

* [Pressure Sensor Guide](https://www.electroschematics.com/pressure-sensor-guide/) by T.K. HAREENDRAN - A similar write-up that goes into additional detail. They didn't de-solder the pressure sensor to identify the component name, but there's lots of good information on this page.

* [bogde/HX711 on GitHub](https://github.com/bogde/HX711) - An Arduino library to interface the Avia Semiconductor HX711 24-Bit Analog-to-Digital Converter (ADC) for reading load cells / weight scales. Code on this page does not use this library, but others may find it helpful.

* [HX710 datasheet (English)](https://www.electronicscomp.com/datasheet/hx710b-ic-datasheet.pdf)

* [Differential pressure sensors](https://www.avnet.com/wps/portal/abacus/solutions/technologies/sensors/pressure-sensors/measurement-types/differential/) - Article about the topic which includes a good example of an instrumentation amplifier.

* [Design tips for a resistive-bridge pressure sensor in industrial process-control systems](https://www.ti.com/lit/an/slyt640/slyt640.pdf) - Texas Instruments application note

* [The Wheatstone Bridge](https://meritsensor.com/the-wheatstone-bridge/) by Michael Daily
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