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docs: fix worked example, encoding table, and CHANGELOG for u8/i8 raw bytes and TX_POWER_MAX

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swaits committed 2026-03-29 20:42:58 -06:00
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CHANGELOG.md
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@@ -20,7 +20,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/).
- RSSI sparkline (1-minute history, TX shown as dotted bars)
- Combined splash/waiting screen on disconnect
- Auto-detect USB host connect/disconnect via DTR
- Config validation against SX1262 hardware limits
- Config validation against per-board hardware limits
- `TX_POWER_MAX` sentinel (`-128`): auto-use the board's maximum TX power
- Board support: Heltec V3, Heltec V4, RAK WisBlock 4631
- Example: MeshCore packet decoder with group channel decryption
docs/PROTOCOL.md
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@@ -64,10 +64,10 @@ Postcard is a compact binary format. The subset used by DongLoRa:
|-------|------|---------------|-------------|-------------|
| `freq_hz` | `u32` | varint | 150,000,000 – 960,000,000 | Frequency in Hz |
| `bw` | `Bandwidth` | varint (0–9) | see table | Signal bandwidth |
| `sf` | `u8` | varint | 5 – 12 | Spreading factor |
| `cr` | `u8` | varint | 5 – 8 | Coding rate denominator (5 = CR 4/5) |
| `sf` | `u8` | raw byte | 5 – 12 | Spreading factor |
| `cr` | `u8` | raw byte | 5 – 8 | Coding rate denominator (5 = CR 4/5) |
| `sync_word` | `u16` | varint | any | LoRa sync word (e.g. `0x3444`) |
| `tx_power_dbm` | `i8` | raw signed byte | board-dependent | TX power in dBm. `-128` = max power for this board. |
| `tx_power_dbm` | `i8` | raw signed byte | board-dependent | TX power in dBm. `-128` = board's max power. |
## Bandwidth
@@ -102,21 +102,23 @@ Configure the radio for 915 MHz, 125 kHz BW, SF7, CR 4/5, sync word `0x3444`,
### 1. Build the RadioConfig
| Field | Value | Varint bytes |
|-------|-------|-------------|
| `freq_hz` | 915,000,000 | `80 84 AF B4 03` |
| `bw` | 7 (125 kHz) | `07` |
| `sf` | 7 | `07` |
| `cr` | 5 (CR 4/5) | `05` |
| `sync_word` | 0x3444 | `C4 E8 00` |
| `tx_power_dbm` | 14 → zigzag 28 | `1C` |
| Field | Value | Wire bytes | Encoding |
|-------|-------|-----------|----------|
| `freq_hz` | 915,000,000 | `C0 95 A7 B4 03` | varint |
| `bw` | 7 (125 kHz) | `07` | varint (enum index) |
| `sf` | 7 | `07` | raw byte |
| `cr` | 5 (CR 4/5) | `05` | raw byte |
| `sync_word` | 0x3444 | `C4 68` | varint |
| `tx_power_dbm` | 14 | `0E` | raw signed byte |
Or use `-128` (`0x80`) for `tx_power_dbm` to request the board's max power.
### 2. Build the SetConfig command
Prepend the variant index for `SetConfig` (index 2):
```
02 80 84 AF B4 03 07 07 05 C4 E8 00 1C
02 C0 95 A7 B4 03 07 07 05 C4 68 0E
```
### 3. COBS-encode and send
@@ -135,12 +137,13 @@ frame, decode it, and the first byte is the response variant index
## Host Implementation Checklist
1. Open the USB serial port (find by VID:PID `1209:5741`)
2. Implement varint and zigzag encoding/decoding
3. Implement COBS encode/decode (use a library — available in every language)
4. Build `SetConfig` with your desired radio parameters
5. Send it, read back `Ok`
6. Send `StartRx`, read back `Ok`
7. Loop: read frames, decode `RxPacket` responses
8. To transmit: send `Transmit` with payload, read back `TxDone`
2. Implement varint encoding/decoding (for `u16`/`u32` and enum variants)
3. Note: `u8` and `i8` are raw bytes, NOT varint/zigzag
4. Implement COBS encode/decode (use a library — available in every language)
5. Build `SetConfig` with your desired radio parameters (use `-128` for max TX power)
6. Send it, read back `Ok`
7. Send `StartRx`, read back `Ok`
8. Loop: read frames, decode `RxPacket` responses
9. To transmit: send `Transmit` with payload, read back `TxDone`
See `examples/` for working Python implementations.