Weird Constructor / Posts / Week of Weird Constructions 1

Week of Weird Constructions 1

The first week of weird constructions started out with this website and the first post. I'm glad the Zola website generator I use for this website works so good. Especially because it's written in Rust.

HexoTK HexKnob

But now to my projects. I've not yet written an introduction for HexoSynth and I wont do it quite now. Only so much: It's an audio synthesis environment with a certain style. And it's one of my big projects I've been working on in 2021. The GUI had quite some development road behind it. Originally I wrote HexoTK quite simple. But I saw performance problems on the horizon, it ate 20% CPU for basically doing nothing. To fix that I needed to cache the widget output. And then I did something I usually don't do, which is using a library that is not "there yet" with tuix. You can find my so far successful try of implementing the GUI here: HexoSynth tuix GUI

I hoped it would become the future of HexoSynth, but tuix development more or less halted for the new VIZIA. After having too many friction points with the declarative style I decided to go back to HexoTK and I completely reimplemented it by now. These days are only consisting of reimplementing all the widgets that were there before. Luckily I can reuse most of HexoSynth tuix GUI, because the drawing code (which is the most complex part) can be reused almost 100%. Big thanks go out to the femtovg 2D vector library for their efforts.

And so I reimplemented one of the most important widgets last week, which is the HexKnob. A fully featured value knob with an iconic shape that fits into HexoSynth just fine. The layout of HexoTK is done by morphorm which is the layout engine I took over from tuix. In the video you see the HexKnob being interacted with the mouse and being rescaled by the GUI layout engine:

Ported HexKnob from tuix_gui to HexoTK

Reading/Writing an SD card with Embedded Rust

I've also worked on a piece of code to read and write an SD card from the Raspberry Pi Pico. That would of course not be a problem if I was using C++ still. But I am using Rust for everything these days, so I dived further in to the embedded Rust ecosystem. And it has been really nice so far. There are traits for all important interfaces on a microcontroller and generic driver implementations are all over So my searches turned up the Embedded SD/MMC crate embedded-sdmmc.

But first I needed to solder myself an SD card holder. Because I did not yet order a set of SD card holders, I decided to quickly DIY one. I've used a Micro SD card adapter and hot glued it onto a perf board as you can see in the following pictures:

The DIY micro SD card mount from an micro SD adapter
The DIY micro SD card mount from an micro SD adapter
The DIY micro SD card mount connected to my Raspberry Pi Pico testing ground.
The DIY micro SD card mount connected to my Raspberry Pi Pico testing ground.

I ended up with relatively straight forward code in Rust. You can find the Rust SD Card SPI example code. in my RustRP2040Code repository.

Here is a snippet from that example, which is not that spectacular, but it shows how usual the high level file accessing code worked:

    cont.iterate_dir(&v, &dir, |ent| {

    let mut file =
            &mut v, &dir, "O.TST",

    let mut buf = [0u8; 32];
    let nr = v, &mut file, &mut buf).unwrap();
    cont.close_file(&v, file).unwrap();

    info!("READ {} bytes: {}", nr, buf);

    let mut file =
            &mut v, &dir, "O.TST",
    cont.write(&mut v, &mut file, b"foobar123\n").unwrap();
    cont.close_file(&v, file).unwrap();

I've run into one issue though. With a completely new SD card it did not work on first try. I've first had to create a new partition with W95 FAT32 (LBA) type, because otherwise the embedded_sdmmc crate would not allow me to access it. One fdisk and one mkfs.fat command later it worked fine though!

Because everything went so easily, I wanted to push my example upstream. There was not an example for accessing an SD card in the rp-pico board support of rp2040-hal crate yet. So I decided to cleanup my hacky example and even document my progress in the SD/MMC SD Card rp-pico board example. Most notably is the little ASCII diagram of how to connect the SD card to the Raspberry Pi Pico:

             Pull Ups ->||||
                        ||| \
     _______________    |||  \
    |     DAT2/NC  9\---o||   \                            _|USB|_
    | S   DAT3/CS   1|---o+----+------SS--\               |1  R 40|
    | D   CMD/DI    2|----o----+-----MOSI-+-\             |2  P 39|
    |     VSS1      3|-- GND   |          | |         GND-|3    38|- GND
    | C   VDD       4|-- +3.3V |  /--SCK--+-+----SPI0 SCK-|4  P 37|
    | A   CLK/SCK   5|---------+-/        | \----SPI0 TX--|5  I 36|- +3.3V
    | R   VSS2      6|-- GND   |  /--MISO-+------SPI0 RX--|6  C   |
    | D   DAT0/DO   7|---------o-/        \------SPI0 CSn-|7  O   |
    |     DAT1/IRQ  8|-[5k]- +3.3V                        |       |
     """"""""""""""""                                     |       |
                                                          |       |
                                                          |20   21|
        - (+) crossing lines, not connected
        - (o) connected lines

The code is much more refined and cleaned up as you can see in a snippet here:

    match cont.open_file_in_dir(&mut volume, &dir, "O.TST", Mode::ReadWriteCreateOrTruncate) {
        Ok(mut file) => {
            cont.write(&mut volume, &mut file, b"\x42\x1E").unwrap();
            cont.close_file(&volume, file).unwrap();
        Err(e) => {
            error!("Error opening file 'O.TST': {}", defmt::Debug2Format(&e));
            blink_signals_loop(&mut led_pin, &mut delay, &BLINK_ERR_6_SHORT);

I even added a simple debug output using the single LED on the Raspberry Pi Pico.

Controlling an WS2812 RGB LED Strip with Rust and the Raspberry Pi Pico

Because it was so fun, I also cleaned up my old WS2812 RGB LED embedded Rust example for the Raspberry Pi Pico which uses the ws2812-pio-rs crate by ithinuel in combination with the smart-leds crate.

My ASCII art skills were demanded once again:

     _______________      /----------------------\
    |+5V  /---\  +5V|----/         _|USB|_       |
    |DO <-|LED|<- DI|-\           |1  R 40|-VBUS-/
    |GND  \---/  GND|--+---\      |2  P 39|
     """""""""""""""   |    \-GND-|3    38|
                       |          |4  P 37|
                       |          |5  I 36|
                       \------GP4-|6  C   |
                                  |7  O   |
                                  |       |
                                  |20   21|

And here a little code snippet from the WS2812 RGB LED embedded Rust example for the Raspberry Pi Pico:

    loop {
        for (i, led) in leds.iter_mut().enumerate() {
            // An offset to give 3 consecutive LEDs a different color:
            let hue_offs = match i % 3 {
                1 => 0.25,
                2 => 0.5,
                _ => 0.0,

            let sin_11 = sin((t + hue_offs) * 2.0 * core::f32::consts::PI);
            // Bring -1..1 sine range to 0..1 range:
            let sin_01 = (sin_11 + 1.0) * 0.5;

            let hue = 360.0 * sin_01;
            let sat = 1.0;
            let val = 1.0;

            let rgb = hsv2rgb_u8(hue, sat, val);
            *led = rgb.into();

        // Here the magic happens and the `leds` buffer is written to the
        // ws2812 LEDs:
        ws.write(brightness(leds.iter().copied(), strip_brightness))

        // Wait a bit until calculating the next frame:
        frame_delay.delay_ms(16); // ~60 FPS

        // Increase the time counter variable and make sure it
        // stays inbetween 0.0 to 1.0 range:
        t += (16.0 / 1000.0) * animation_speed;
        while t > 1.0 {
            t -= 1.0;

I've never written microcontroller code as straight forward and easily as with the embedded Rust ecosystem. Here a few crates and links at the core of all these:

Improving rp-pico Documentation

Last notably I also spent some time on improving the documentation of the board support in rp-pico: improved rp-pico pin documentation. A pull request upstream has been submitted. I hope it improves the documentation a bit, so that others that dive into this ecosystem have a slightly better experience. That is not to say that I did not have a good experience. But I believe the Rust crates for the Raspberry Pi Pico deserve better documentation.

I've collected a few links this week too that I don't want to forget right now:

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Weird Constructor

Nice end 30 y/o guy, geek and F(L)OSS developer that messes with: Linux, Windows, Networking, Interpreters/Compilers, Games, Audio, GUIs, C/C++, Rust, Scheme/Lisp, 3D printing, electronics and more.

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