F Prime SAMD21 reference deployment

A small, complete, buildable F Prime flight-software deployment for the Microchip SAMD21 Curiosity Nano (ATSAMD21G17D, ARM Cortex-M0+, 128 KiB flash, 16 KiB RAM), running baremetal.

This repository builds off of other repositories:

• SAMD21 Drivers fprime-samd
• fprime-baremetal OSAL

One submodule pin is temporary: lib/fprime points at lestarch-autobot/fprime branch samd-reference-kronos3-upstream-devel — the previous Kronos3/fprime upstream pin merged with nasa/fprime devel (which carries nasa/fprime#6237: Drv.AsyncSpi / Drv.AsyncGuardedSpi, AsyncSpiCfg). Move the pin back to Kronos3/fprime once its upstream branch picks up that devel. config-samd-reference/AsyncSpiCfg.fpp sizes the async SPI driver at four slots for this deployment.

Hardware

The SAMD21 Curiosity Nano (Microchip part number DM320119) and nothing else. Optional: an I2C device for I2cTester to talk to, and a jumper between the two GPIO pins so GpioIn can see what GpioOut drives.

Function	Pin(s)	Peripheral
Uplink / downlink UART	PA22 (TX), PB22 (RX)	SERCOM5, 115200 8N1, LSB first
I2C	PA12 (SDA), PA13 (SCL)	SERCOM4, 400 kHz fast mode
GPIO input	PA23	pull-up, EIC interrupt on both edges
GPIO output	PA25	push-pull
Rate-group tick	—	RTC, ultra-low-power 32 kHz oscillator, 8 Hz

PA22 / PB22 are the pins the Curiosity Nano routes to its on-board nEDBG debugger's USB CDC virtual COM port (CDC RX / CDC TX in the kit user guide), so the single USB cable that powers and programs the board also carries uplink / downlink — no external USB-serial adapter is needed. To use a different UART instead, re-pin comDriver in CuriosityReference/Top/instances.fpp.

Quickstart

git clone --recursive https://github.com/fprime-community/fprime-samd-reference.git
cd fprime-samd-reference

python3 -m venv venv
. venv/bin/activate
pip install -r requirements.txt

fprime-util generate samd21g17
fprime-util build -j"$(nproc)" -p CuriosityReference samd21g17

The build prints an arm-none-eabi-size -A table and leaves artifacts in build-artifacts/samd21g17/CuriosityReference/:

bin/CuriosityReference.elf        linked image
bin/CuriosityReference.elf.bin    raw binary, loads at 0x0000
bin/CuriosityReference.elf.hex    Intel HEX
bin/CuriosityReference.map        linker map
bin/CuriosityReference.nm         symbol sizes
bin/CuriosityReference.objdump    disassembly
dict/TopTopologyDictionary.json   the dictionary the ground system reads

Always generate with fprime-util — it's what passes settings.ini's library_locations and default_cmake_options to CMake; a bare cmake --preset ... never reads settings.ini. Once the cache exists, the presets in CMakePresets.json share fprime-util's binaryDir, so you can also drive the build directly:

cmake --build --preset samd21g17

A faster clone

--recursive pulls the complete F Prime history, which is large. Neither the build nor the tools need it:

git clone --recursive --shallow-submodules \
    https://github.com/fprime-community/fprime-samd-reference.git

or, to keep full history but skip file contents you never check out:

git clone --recursive --filter=blob:none \
    https://github.com/fprime-community/fprime-samd-reference.git

The cross toolchain

lib/fprime-samd/cmake/toolchain/samd21-bare-toolchain.cmake finds arm-none-eabi-gcc, CMSIS and CMSIS-Atmel by absolute path under ~/.arduino15/packages/adafruit/tools, at pinned versions, with no /usr/bin fallback and no non-Arduino branch for CMSIS. An apt-installed gcc-arm-none-eabi won't be found, and wouldn't supply the SAMD21 device headers (sam.h) anyway. Install the toolchain the way the toolchain file expects:

arduino-cli core update-index \
    --additional-urls https://adafruit.github.io/arduino-board-index/package_adafruit_index.json
arduino-cli core install adafruit:samd@1.7.17 \
    --additional-urls https://adafruit.github.io/arduino-board-index/package_adafruit_index.json

Don't float that version: 9-2019q4, 5.4.0 and 1.2.2 are literal path components in the toolchain file, and a core bump that moves any tool version breaks path resolution with a FATAL_ERROR at configure time.

Or use the devcontainer, which does all of this for you.

Flashing

With a J-Link probe on the SWD pads:

python3 scripts/jlink_flash.py CuriosityReference

The script discovers deployments from the root CMakeLists.txt, reads default_toolchain from settings.ini, selects ATSAMD21G17A (JLinkExe has no D variant; the geometry is identical), and loads the .bin at 0x0000 — there's no bootloader on this board. scripts/flash.jlink is the command template it renders.

The on-board nEDBG debugger speaks CMSIS-DAP rather than J-Link's protocol. To flash through it instead, point pymcuprog or OpenOCD at the same .bin:

openocd -f interface/cmsis-dap.cfg -c "transport select swd" -f target/at91samdXX.cfg \
    -c "program build-artifacts/samd21g17/CuriosityReference/bin/CuriosityReference.elf.bin 0x00000000 verify reset exit"

Running the ground system

fprime-gds -n \
    --dictionary build-artifacts/samd21g17/CuriosityReference/dict/TopTopologyDictionary.json \
    --packet-set-name Main \
    --communication-selection uart \
    --uart-device /dev/ttyACM0 \
    --uart-baud 115200 \
    --framing-selection fprime

-n because the binary runs on the board, not the host. --packet-set-name Main selects the packet set the topology declares (telemetry packets Main); telemetry here is packetized, not per-channel, so without it the GDS can't decode the stream. /dev/ttyACM0 is the nEDBG virtual COM port (the same USB cable used for flashing). --framing-selection fprime because the deployment frames with the F Prime protocol and newer fprime-gds releases default to CCSDS space packets.

Contributing

See CONTRIBUTING.md. Briefly: build before you push, run fprime-util format over your changes, and watch the flash/RAM delta CI posts on your pull request — this repository's whole claim is that F Prime fits in 128 KiB.

License

Apache-2.0. See LICENSE and NOTICE. The submodules under lib/ keep their own licenses and are not redistributed here.