Go library implementing an Attitude and Heading Reference System (AHRS) for the Stratux ADS-B receiver, along with sensor drivers (BMP280 barometer, ICM-20948 IMU), offline simulation, magnetometer calibration, and a websocket visualization server.

See CLAUDE.md for the full architecture overview and known TODOs.

Requires Go 1.22 or newer.

go mod tidy
go build ./...
go test ./ahrs/...

The sensor test/ binaries (./sensors/bmp280/test, ./sensors/icm20948/test) compile on any platform but only function on a Raspberry Pi (or similar SBC) with the corresponding chip wired to the I²C bus.

Enable I²C bus 1 in raspi-config (or dtparam=i2c_arm=on in /boot/firmware/config.txt). After that:

• BMP280 is read through the kernel's IIO driver (no direct I²C bit-banging from userspace). Bind the driver one of two ways:

  # Persistent: add to /boot/firmware/config.txt and reboot
  dtoverlay=i2c-sensor,bmp280,addr=0x76   # or addr=0x77
  
  # Per-session: instantiate via sysfs (no reboot)
  sudo modprobe bmp280-i2c
  echo bmp280 0x76 | sudo tee /sys/bus/i2c/devices/i2c-1/new_device
  # Tear down with:
  echo 0x76 | sudo tee /sys/bus/i2c/devices/i2c-1/delete_device

  Verify with cat /sys/bus/iio/devices/iio:device0/name — it should print bmp280. Then go run ./sensors/bmp280/test prints a CSV of live readings.

• ICM-20948 uses an out-of-tree kernel module that lives in a sibling repo, westphae/icm20948-mod. Build and install it, then load the hrtimer trigger module that goflying's streaming capture needs:

  # Persistent: build + install dtbo + reboot
  cd ../icm20948-mod
  make && sudo make install
  sudo reboot
  
  # Per-session: insmod + bind via sysfs (no reboot)
  sudo insmod ./icm20948.ko
  echo icm20948 0x68 | sudo tee /sys/bus/i2c/devices/i2c-1/new_device   # or 0x69
  # Tear down with:
  echo 0x68 | sudo tee /sys/bus/i2c/devices/i2c-1/delete_device
  sudo rmmod icm20948
  
  # Always required (once per boot) before streaming:
  sudo modprobe iio-trig-hrtimer

  To make the trigger module load automatically on every boot, drop a one-line file into /etc/modules-load.d/:

  echo iio-trig-hrtimer | sudo tee /etc/modules-load.d/iio-trig-hrtimer.conf

  (The BMP280 driver autoloads via the device-tree overlay above, so no equivalent file is needed for it.)

  Verify with cat /sys/bus/iio/devices/iio:device*/name — one of them should print icm20948. Then sudo go run ./sensors/icm20948/test prints a live TUI of accel/gyro/mag/temp readings. Root is required because go-iio creates the hrtimer trigger via configfs.

Two downstream projects live alongside this repo in GOPATH:

• magkal — Go-modules build that uses goflying via replace github.com/westphae/goflying => ../goflying. Mostly exercises sensors/icm20948.
• stratux — GOPATH-style; consumes goflying as a git submodule. Pinned to a specific commit, so canonical goflying changes only reach stratux when its submodule pointer is bumped.