Initial import: Rust BLE-MIDI keypad for Pico W

Port of the C/BTstack BLE-MIDI keypad firmware to Rust (embassy + cyw43 +
trouble). 16-pad RGB keypad (APA102 SPI + I2C button expander), BLE-MIDI 1.0
GATT server (full codec: sysex, running-status, real-time), octave display
on BOOTSEL, onboard LED heartbeat, USB serial logging.

- src/keypad.rs      Pimoroni RGB Keypad driver
- src/midi_keypad.rs pad->Note On/Off + LED response state machine
- src/codec.rs       BLE-MIDI 1.0 codec (port of rppicomidi, MIT)
- src/main.rs        cyw43 BT bring-up + trouble GATT + MIDI pump
- src/octave.rs      octave digit display on BOOTSEL

GPL-3.0-or-later; codec.rs retains its MIT (rppicomidi) attribution.

README.md

@@ -0,0 +1,47 @@
+# pico-pi-midi (Rust)
+
+BLE-MIDI keypad firmware for the Raspberry Pi Pico W (RP2040 + CYW43439), written in Rust using [embassy](https://embassy.dev), the [cyw43](https://crates.io/crates/cyw43) driver (Bluetooth), and the [TrouBLE](https://github.com/embassy-rs/trouble) BLE host.
+
+This is the Rust port of the original C/BTstack firmware (now kept separately as `pico-pi-midi-c`). It talks BLE-MIDI 1.0 to iOS / macOS Core MIDI, turning the Pimoroni Pico RGB Keypad into a 16-pad wireless MIDI controller.
+
+## What it does
+
+- **16-pad keypad** (Pimoroni RGB Keypad Base): reads buttons over I²C (GPIO expander @ 0x20) and drives APA102 RGB LEDs over SPI (CS=17, SCK=18, MOSI=19).
+- **BLE-MIDI 1.0** GATT server (MIDI Service `03B80E5A-…`), advertised so Core MIDI discovers it as a MIDI device. Pad presses → Note On/Off over Bluetooth; incoming Note On lights the pad.
+- **Octave display**: the BOOTSEL button cycles the keypad's note offset by +12 and flashes the active octave as a digit on the 4×4 grid for 500 ms.
+- **Onboard LED** heartbeat (driven via the CYW43 chip — the Pico W's LED is on the wireless chip, not an RP2040 pin).
+- **USB serial logging** via `embassy-usb-logger` — connect and read with `screen /dev/cu.usbmodem* 115200` to see boot/advertising logs.
+
+## Roadmap
+
+This is v1: a BLE-MIDI keypad. The goal is a **flexible MIDI router** — MIDI over USB, BLE, keypad, TRS, and 4 stereo CV outputs, with channels configurable at runtime via an LCD. See the architecture notes (kept in the session memory) for the plan.
+
+## Building
+
+Requires Rust stable (≥1.93) and the `thumbv6m-none-eabi` target:
+
+```sh
+rustup target add thumbv6m-none-eabi
+cargo build --release
+```
+
+The CYW43 firmware blobs (`cyw43-firmware/*.bin`) are committed here so no network access is needed at build time. They are redistributable under the permissive binary license in the upstream [`embassy cyw43-firmware`](https://github.com/embassy-rs/embassy/tree/main/cyw43-firmware) directory.
+
+## Flashing
+
+```sh
+cargo build --release
+elf2uf2-rs convert target/thumbv6m-none-eabi/release/rgb-keypad target/uf2/rgb-keypad.uf2
+# hold BOOTSEL + plug in the Pico W, then:
+picotool load target/uf2/rgb-keypad.uf2 -x
+```
+
+## License
+
+GPL-3.0-or-later (see [`LICENSE`](LICENSE)).
+
+`src/codec.rs` is a Rust port of the BLE-MIDI 1.0 packet codec from
+[rppicomidi/pico-w-ble-midi-lib](https://github.com/rppicomidi/pico-w-ble-midi-lib),
+which is MIT-licensed; that attribution is retained in the file header. MIT is
+GPL-3.0-compatible, so the repository as a whole is GPL-3.0-or-later while that
+file preserves its MIT provenance.