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Table of Contents

• What is haxo-rs?
• Required System Configuration
  • Hardware
  • Overlay Filesystem
  • I2C
  • Sound Card
• Software Development Setup
  • Package dependencies
• Running the code
  • Logging
• Testing
• Running on boot

What is haxo-rs?

haxo-rs is a the application that runs on a haxophone to convert key presses into music.

The application is written in Rust. It compiles and runs on a Raspberry Pi.

Required System Configuration

Hardware

The Raspberry Pi needs to have a Haxophone HAT attached to it.

Overlay Filesystem

For reliability, we recommend keeping the root file system as read-only on the SD card, and keep your software development limited to separate (writable) USB drive.

This can be configured via raspi-config.

I2C

You need to enable I2C on your Raspberry Pi. The recommended and easiest way to do that with with raspi-config.

Sound Card

To use the audio codec on the Haxo HAT, you need to load the max98357a driver. You can do that by editing /boot/firmware/config.txt as shown below

# Enable audio (loads snd_bcm2835)
# dtparam=audio=on
dtoverlay=max98357a

Software Development Setup

Software is developed on a headless (i.e. no display) Raspberry Pi. The development host runs VSCode and connects to the headless Pi over ssh.

The diagram below shows the development setup we use on the Pi Zero. On the RP3 or 4 the setup is simpler as it has built-in USB and Ethernet.

An alternative setup could be to go full native on the Raspberry Pi, running your IDE there.

Package dependencies

You will need to install fluidsynth and its development libraries

apt install libfluidsynth-dev fluidsynth

Running the code

You can compile and run haxo-rs with cargo.

cd haxo-rs
cargo run

Logging

The application uses env_logger to produce logs. You can enable debug logs as by setting the RUST_LOG environment variable, for instance:

RUST_LOG=debug cargo run

Testing

You can run unit tests with cargo test -- --test-threads=1. The tests cannot run in parallel as they will collide accessing hardware resources (GPIO, I2C bus, etc.). The option --test-threads=1 disables parallel execution of tests and forces them to run sequentially.

running 8 tests
test keyscan::tests::all_keys ... ignored
test keyscan::tests::init ... ok
test keyscan::tests::read ... ok
test notemap::tests::update ... ok
test pressure::tests::init ... ok
test pressure::tests::pressure_step ... ignored
test pressure::tests::read ... ok
test pressure::tests::read_io ... ignored

test result: ok. 5 passed; 0 failed; 3 ignored; 0 measured; 0 filtered out; finished in 0.02s

Note that there are some ignored tests as well. These are disabled by default because they require user input to pass. But they are useful to test hardware (e.g. stuck keys, dead pressure sensor, etc.). To run, enable standard output as:

pi@raspberrypi-one:/media/usb/haxo-rs $ cargo test all_keys -- --nocapture --ignored
    Finished test [unoptimized + debuginfo] target(s) in 0.16s
     Running unittests (target/debug/deps/haxo001-c08e384db0cbfdd8)

running 1 test
Press all the keys at least once, in any order...
01/22: detected_keys: 400 keys: 400
01/22: detected_keys: 0 keys: 400
(...)
21/22: detected_keys: 0 keys: 27773777
22/22: detected_keys: 8 keys: 2777377f
test keyscan::tests::all_keys ... ok

test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 6 filtered out; finished in 11.45s

Running on boot

If you followed the advice to keep the sd card read-only, you will need to make it writable before making the changes below.

Now copy the haxo binary somewhere in your sd card and invoke it from /etc/rc.local.

cp /media/usb/haxo-rs/target/debug/haxo001 /usr/local/bin
echo /usr/local/bin/haxo001 >> /etc/rc.local

Now you can write-protect the SD card again.