Flight Software for Crater Maker Special

See write-up on sagarpatil.me

Data Sources / Sinks

Overview

• MCU: RP2040
• RTOS: FreeRTOS
• HAL: pico-sdk

Branches

Information as of Aug 28, 2023, bother Sagar if you want it updated

• main: development branch, contains latest (mostly) tested code, broken code is not allowed, POC is Sagar Patil
• cmdnet-secure: encrypted version of CommandNet, POC is Sagar Patil, information on Confluence
• ads13x: driver development for ADS13xMXX ADCs, POC is Mihir Patil
• lte-modem: LTE modem driver, POC is Jay Jagani
• stuff_on_pi: random stuff from Taylor's Pi, should probably merge it, POC is Sagar Patil
• freertos: exploratory branch for FreeRTOS, POC is Sagar Patil and Charlie Schoettle
• vn200: driver for the VN200 IMU, POC is Charlie Schoettle
• tests: working test framework, but dead branch, POC is Sagar Patil
• host-compilation: dead branch, host compilation for testing purposes, POC is Jay Jagani (?)
• camerons-stuff: Dead branch, old code written for the ATMega328p, archival, POC is Cameron Williams

Filesystem Hirearchy

PSPL_CMS_Avionics_Code/
├── README.md <- This file
│
│
├── src/ <- contains main programs for each board
│   └── someprogram/ <- Main program folder, i.e., for a board
│       ├── someprogram.h <- All header stuff for this program
│       ├── main.c <- Contains the entrypoint
│       └── other.c <- Other source files
├── lib/ <- common libraries shared by all boards
│   └── example/ <- example library
│       ├── example.c
│       └── include/ <- header files, added to include path
│           ├── example.h <- top level header, included with `#include <example.h>`
│           └── example/ <- secondary headers
│               └── whatever.h <- included with `#include <example/whatever.h>`
├── device/ <- Same structure as lib, but for device drivers
│
│
├── external/ <- Gitignored, for automatically downloaded libraries(in Makefile), contains pico-sdk
├── build/ <- not uploaded to the repo, contains compilation outputs
│   └── bin/ <- contains the files to be uploaded to the boards
│
│
├── .clang-format <- file containing autoformatter rules
├── .gitignore <- file containing things to not be uploaded to GitHub(e.g., exe's, build folder)
├── Doxyfile <- Doxygen Documentation Generator Configs, mostly autogenerated
├── CMakeLists.txt <- Main build script
└── Makefile <- User-friendly build script, calls CMake

Explaining the Contents of device/ and /lib

device/

This folder contains abstractions for interacting with external hardware (drivers), and also contains low level RP2040 specific stuff, such as a custom implementation of spi under myspi/.

All of the subfolders explained

• myspi/ - This exists solely due to FreeRTOS. It uses FreeRTOS mutexes so that multiple tasks can communicate with devices over SPI. For a brief summary of how it works:
  • Start a DMA transfer when myspi_transfer is called
  • Yield the current process and wait for a task notification
  • When the DMA transfer completes, it raises an interrupt
  • Interrupt sends a notification to the task owning the transfer
  • Task continues execution
• mydma/ - Contains a memcpy implementation which uses RP2040's DMA to copy memory without using the CPU. Operation is similar to myspi, but instead of data being copied to a peripheral, it's copied across memory on the RP2040.
• myuart/ - FreeRTOS supporting UART driver

All subsequent drivers use the above three drivers. Most of them use myspi

• ads13x/ - Driver for the ADS13xMXX ADCs
• max31856/ - Thermocouple amplifier and ADC driver
• w25n01/ - Flash driver
• w5500/ - Ethernet driver

Usage

Dependencies

• git (to clone this repo)
• make (for running CMake)
• ninja (CMake backend)
• cmake (build system)
• compdb (compile database for headers, optional)
• gcc-arm-none-eabi (compiler)
• ccache (compiler cache, optional)
• newlib-arm-none-eabi (C standard library)

Cloning this Repo

Just clone it like you normally would

Working on a project

All Setup and Development Operations information is on Confluence.

Building

Run make or make build for a debug build, or make release for a release build. make clean will delete the build folder.

Output binaries for each board will be present in build/bin/. ELF binaries can be found in build/bin/elf/

Remote Dev on Bang Bang Boom Box

Overview

• Raspberry Pi 4, running Raspberry Pi OS
• 0-2 Pi Picos connected at any time, ask in #avionics for which boards are connected
  • Connected over USB
  • BOOTSEL (puts the Pico into a flashable state) and RUN (reset) connected to Pi's GPIO

There's Pico A and Pico B, each with a set of bootsel and reset pins.

You can see how many Pico's are connected by running lsusb

Dependencies

• Zerotier VPN
• SSH
• VSCode (optional)

Setup

• Install Zerotier, ask Sagar for the network ID
• Join the network
• SSH into the Pi

VSCode Setup

• Install the Remote SSH extension
• Use the extension to connect to the Pi

Flight software is located in ~/Documents/FlightSoftware_CMS

Flashing Code

There are scripts under scripts/ that can be used to flash code to the Pi. They are:

• flash.sh: Copy the UF2 file to the Pico (this flashes the Pico)
• pico.py: See later, this can be used to bootsel and reset the Pico
• router.sh: (Legacy, do not execute) Used to setup the Pi as a router

1. Decide which Pico you want to use (A or B)
2. Run ./scripts/pico.py <A/B> bootsel
   • Example: ./scripts/pico.py A bootsel
   • This will put the Pico into a flashable state
   • You can verify this by running lsusb, you'll see that one of the Pico's is listed as "Raspberry Pi Pico Boot" or something similar
3. Run ./scripts/flash.sh <board-name>
   • Example: ./scripts/flash.sh ntp-test
   • This will flash the Pico
4. To see the output, run cat /dev/ttyACM0
   • If multiple Picos are connected, use ls /dev/ttyACM* to list all the output ports.
   • Your Pico can be either /dev/ttyACM0 or /dev/ttyACM1, try both

If at any point you want to reset the Pico, run ./scripts/pico.py <A/B> reset

FAQ

Q: I'm getting a Permission Denied error when running ./scripts/pico.py or ./scripts/flash.sh

A: Wait a bit longer, the Pico is still booting up. If it's been more than 30 seconds, ask Sagar.

Q: Sagar isn't responding, what do I do?

A: If waiting doesn't fix the permission problem, try this

1. Reset both Picos (doesn't matter if they exist or not)
   • ./scripts/pico.py A reset
   • ./scripts/pico.py B reset
2. Run sudo rm /media/pspl/RPI-RP2*
   • This deletes any stray mount points left behind, which is probably what's causing the script to fail

Q: There aren't any Pico's listed when I run lsusb

A: Reboot the Raspberry Pi by running sudo reboot. Exit your terminal, and wait a bit for the Pi to reboot. Then SSH back in and try again.

Q: That didn't work, what do I do?

A: Contact Sagar and Taylor on the #avionics channel on Slack.