KeyBoard_QT/docs/firmware_proto_transport.md

# Firmware Proto Transport

## Goal

Add CDC and GATT private communication without rewriting the existing keyboard,
time, theme, and LED business logic.

The firmware side should:

- keep standard HID behavior for normal keys
- receive host commands over CDC and GATT
- report private state and function key events over CDC and GATT
- reuse existing modules where possible

## Completed Nodes

### Node 1: internal function events

Files:

- `src/events/function_bitmap_event.h`
- `src/events/function_bitmap_event.c`
- `src/events/function_key_event.h`
- `src/events/function_key_event.c`

Design notes:

- `function_bitmap_event` carries the 29-byte function bitmap from host
- `function_key_event` carries usage + action when a configured function key
  is pressed or released
- these events isolate transport modules from keyboard internals

## Planned next nodes

- keyboard split logic uses `function_bitmap_event`
- CDC transport module
- GATT transport module
- nanopb integration and generated protocol code

### Node 2: keyboard split point

Files updated in this step:

- `src/modules/keyboard_module.c`

Design notes:

- reuse the existing keymap and HID path
- add one explicit split point before HID submission
- keep normal keys on HID
- send configured function keys to private transport only

Implemented behavior:

- store the 29-byte function bitmap
- for keyboard usages marked as function keys:
  - stop normal HID reporting
  - emit `function_key_event`
- for consumer usages marked as function keys:
  - stop normal HID reporting
  - emit `function_key_event`