xiao-samd21-midi2

midi2cpp | Device MIDI 2.0

Seeed Studio XIAO SAMD21

USB MIDI 2.0 device on the XIAO SAMD21 (Cortex-M0+, 32 KB SRAM). Native CMake build via TinyUSB's family_support.cmake, no Arduino IDE.

USB identity

Field	Value
VID:PID	cafe:40F0 (development-only)
Product	XiaoSAMD21
Manufacturer	github.com/sauloverissimo

Build

Requires CMake 3.20+, arm-none-eabi-gcc, Python 3.

cmake -B build         # first run fetches TinyUSB + SAMD21 SDK
cmake --build build -j

Convert to UF2:

python3 build/_deps/tinyusb-src/tools/uf2/utils/uf2conv.py \
    -c -b 0x2000 -f SAMD21 \
    -o build/xiao-samd21-midi2.uf2 build/xiao-samd21-midi2.bin

Pointing at a local TinyUSB checkout: cmake -B build -DTINYUSB_PATH=/path/to/tinyusb.

Flash

The XIAO has no Reset button, only two RST pads at the USB-C end. Enter UF2 bootloader by:

• bridging the RST pads twice within 500 ms, or
• stty -F /dev/ttyACM<N> 1200; sleep 1 (1200 bps touch).

Drop build/xiao-samd21-midi2.uf2 on the mounted Arduino drive. Or use bossac:

sudo bossac -i -d --port=/dev/ttyACM<N> --offset=0x2000 -w -v build/xiao-samd21-midi2.bin -R

Validation

lsusb | grep cafe:40F0
amidi -l                        # IO  hw:N,1,0  Group 1 (Main)
PORT=$(aseqdump -l | grep -i XiaoSAMD21 | awk '{print $1}' | tr -d ':')
timeout 8 aseqdump -p ${PORT}   # chromatic walk C4..G#4

Spec coverage

Tier C (minimal core). No SysEx, no Profile Configuration, no Property Exchange, no Process Inquiry, due to SAMD21 SRAM budget. Full Tier A coverage on a SAMD21-class chip belongs to the upcoming xiao-samd51-midi2 (4× the SRAM).

UMP MT	Spec	Notes
0x0 Utility	M2-104-UM §3	JR heartbeat, 500 ms
0x4 MIDI 2.0 Channel Voice	M2-104-UM §7	NoteOn/Off + 32-bit CC #74 sweep
0xF UMP Stream	M2-104-UM §10	Endpoint Discovery, Device Identity, Endpoint Name, Product Instance ID, Stream Config Notify, FB Info, FB Name

MIDI-CI: Discovery responder only (MUID, Manufacturer, Family, Model, Version).

Showcase

Always on while mounted: JR heartbeat (500 ms), UMP Stream + MIDI-CI Discovery responders, PA17 LED lit.

Per cycle (~6.5 s):

Window	Detail
0 to 4.0 s	Chromatic walk C4 → G#4 (8 steps, 500 ms each), 16-bit velocity ramp 0x2000 → 0xFFFF, 32-bit CC #74 sweep 0x20000000 → 0xFFFFFFFF
4.0 to 4.5 s	Final NoteOff
4.5 to 6.5 s	Gap

License

MIT, inherits parent midi2cpp LICENSE.