#Rynk Protocol Reference

Current protocol version: 0.1.

Every transport (USB CDC, BLE GATT, BLE HID) carries the same frame — a 5-byte header plus a postcard-encoded payload:

┌──────────────┬───────────┬────────────────────┐
│ CMD u16 LE   │ SEQ u8    │ LEN u16 LE         │  ← 5-byte header
├──────────────┴───────────┴────────────────────┤
│              postcard-encoded payload         │  ← LEN bytes
└───────────────────────────────────────────────┘

• Requests use CMD 0x0000..=0x7FFF. The response echoes CMD and SEQ and wraps its payload in postcard Result<T, RynkError> (T = () for Set*).
• Topics use CMD 0x8000..=0xFFFF (server → host push, SEQ 0, bare payload).

Which commands a firmware answers depends on the RMK Cargo features it was built with: a row with no Feature is present once rynk is on, and the rest need their feature (_ble, split, …) compiled in. A command the firmware wasn't built with answers UnknownCmd.

#Endpoints

#Topics

Topics are best-effort pushes; the Get* endpoints above mirror their payloads so a host can recover a missed push.

#Compatibility

• GetVersion (0x0001) and its Result<ProtocolVersion, RynkError> reply are frozen across all versions.
• Within a major version, adding a CMD or topic is a minor bump: old firmware answers UnknownCmd, old hosts ignore unknown topics.
• Reshaping an existing request/response — including appending a field — is a major bump.