Add Driver for the S Band Radio

Description

This pull request defines an SBand component which wraps the RadioLib driver for the SX1280 LoRa radio (hereafter the "S band radio"). RadioLib is a popular set of drivers for embedded-friendly radios and it has been added as a submodule in lib/RadioLib. The component implements the Svc.Com interface and produces two telemetry channels: LastRssi and LastSnr.

This pull request also adds an instance sband of the SBand component to our main deployment. The driver interfaces with hardware via F Prime primitives, so the pull request instantiates these hardware dependencies (spiDriver, gpioSbandNrst, gpioSbandRxEn, gpioSbandTxEn, gpioSbandIRQ) and makes the requisite connections. Requisite changes to the devicetree have been made as well.

A ComCcsdsSband subtopology has also been defined and instantiated. It connects the S band radio to the master communication stack via the pre-existing ComSplitter components.

CircuitPython code defining a Uart-to-S-band-radio passthrough to validate the driver has been added. It depends on the PySquared flight software like the existing LoRa passthrough code and it can be found in circuit-python-sband-passthrough).

Finally, the name of the RFMx module has been fixed for the existing LoRa passthrough.

The SBand component uses a polling approach to detect incoming packets. An interrupt-driven design on the pattern of the existing LoRa radio was impossible because the IRQ lines for the S band radio are connected via the MCP23017 GPIO expander, whose interrupt lines are not connected to the MCU.

The SBand component is an active component. This design decision was necessary because the polling handler must be very short to prevent rate-group slippage, but when a packet has arrived, expensive handling is required. When SBand is active, the expensive handling can be deferred off the rate group and onto the component’s own thread.

To sidestep the need for complicated mutex code to prevent concurrent access to the SPI driver, all code touching the hardware runs inside async handlers that are called sequentially by the component’s thread. This includes the IRQ polling operation itself, ensuring that all SPI access is serialized.

These async ports are all internal and are triggered by synchronous external ports. This approach is more complicated than making the external ports async themselves, but it is necessary to check for and avoid queuing duplicate events. Otherwise the RX polling event, triggered at 10 Hz, could overflow the task queue when a heavier task like transmit or receive is running.

Related Issues/Tickets

Closes #24

How Has This Been Tested?

The driver has been manually tested by connecting a GDS instance to board flashed to be a Uart-to-S-band-radio passthrough and validating manually that:

• Commands sent by the GDS instance via the passthrough are received by the board running ReferenceDeployment
• Events produced by the board running ReferenceDeployment are received by the GDS instance via the passthrough
• Telemetry produced by the board running ReferenceDeployment are received by the GDS instance via the passthrough

I made these scripts to ease testing, you might find them useful as well (especially the serial/by-id trick and the --gui-port option:

#!/usr/bin/env bash

source fprime-venv/bin/activate
fprime-gds --uart-device $(realpath /dev/serial/by-id/usb-*ProvesKit*-if02) --gui-port 5001

#!/usr/bin/env bash

source fprime-venv/bin/activate
fprime-gds --uart-device $(realpath /dev/serial/by-id/usb-Z*)

#!/usr/bin/env bash

screen /dev/serial/by-id/usb-*ProvesKit*-if00 # PySquared Firmware

Checklist

• Written detailed sdd with requirements, channels, ports, commands, telemetry defined and correctly formatted and spelled
• Have written relevant integration tests and have documented them in the sdd
• Have done a code review with
• Have tested this PR on every supported board with correct board definitions

Further Notes / Considerations

lib/RadioLib/src/BuildOptUser.h has some debug #defines which can be uncommented to enable RadioLib logging. This was very helpful for debugging.