# MIDI over BLE

> Original: [MIDI over BLE](https://tttapa.github.io/Control-Surface/Doxygen/db/d99/md_pages_MIDI-over-BLE.html)

BLE MIDI uses BTstack to advertise a standard MIDI BLE service. Compatible with macOS, iOS, Windows 10+, and Android.

## Backend

cs-midi uses the `BTstackBackgroundBackend`, which runs BLE asynchronously but requires periodic `update()` calls for outgoing message buffering.

The convenience typedef:

```cpp pico
using BluetoothMIDI_Interface = GenericBLEMIDI_Interface<BTstackBackgroundBackend>;
```

## Basic usage

```cpp pico
#include "pico/stdlib.h"
#include "pico/cyw43_arch.h"
#include <cs_midi.h>

using namespace cs;

BluetoothMIDI_Interface midi;

NoteButton button {5, {MIDI_Notes::C[4], Channel_1}};

int main() {
    stdio_init_all();
    if (cyw43_arch_init()) return 1;
    Control_Surface.begin();
    while (true) {
        Control_Surface.loop();
        sleep_ms(1);
    }
}
```

`cyw43_arch_init()` is required to bring up the radio before BLE operations.

## HID keyboard + Battery Service

Build with `CS_MIDI_HID_KEYBOARD=ON` to advertise as a BLE HID keyboard alongside MIDI:

1. **Auto-reconnect** — the host OS auto-reconnects to bonded HID peripherals on power-up, bringing up the MIDI service without manual intervention.
2. **Battery level** — the standard Battery Service (UUID 0x180F) reports charge level. Update with:

```cpp pico
setBLEBatteryLevel(percent);
```

No keyboard input is sent — the HID descriptor exists solely to trigger OS auto-connect behavior and surface the battery indicator.

## Radio module

The BLE transport requires a CYW43 radio. Only the **Infineon RM2 module** has been tested. A board file for the Waveshare RP2350B Plus W (RM2-equipped) is provided at `boards/waveshare_rp2350b_plus_w.h`.