portersky
df3d399610
Switch CRC from CCITT (0x07) to DVB-S2 (0xD5) to match ELRS. Adopt ELRS USB frame format: [addr][length][type][payload][crc]. Update frame type constants to match current ELRS protocol values. New skeleton modules (stub implementations with TODO comments): - crsf_telemetry.h/.c: telemetry decoders (GPS, battery, link..) - crsf_stream.h/.c: incremental streaming frame reader - crsf_param.h/.c: parameter protocol (read/write/set_power) Retained old frame format as *_legacy functions for backward compatibility with existing telemetry tool and tests. Add cel_serial_find_elrs_port() and cel_serial_open_probe() stubs to serial module for port auto-detection and baud probing.
142 lines
4.3 KiB
Markdown
142 lines
4.3 KiB
Markdown
# celrs
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A C23 project for interfacing with ELRS TX modules (e.g., BAYCK Nano Dual
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Band) via serial USB using the CRSF (Crossfire Serial) protocol.
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Built on the same TDD foundation as [ctdd](https://github.com/PorterSky/ctdd)
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using [Unity](https://github.com/ThrowTheSwitch/Unity) and
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[CMock](https://github.com/ThrowTheSwitch/CMock).
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All dependencies are fetched automatically via CMake `FetchContent` — no
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manual installation required beyond the tools listed below.
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## Requirements
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| Tool | Purpose |
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| ------------ | ----------------------------------------------------- |
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| CMake ≥ 3.21 | Build system |
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| Ninja | Build backend |
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| C23 compiler | GCC 14+, Clang 18+ |
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| Ruby ≥ 3.0 | CMock mock generation |
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| gcovr ≥ 6.0 | Coverage reports — optional (`uv tool install gcovr`) |
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## Build
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Configure:
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```sh
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cmake -S . -B build -G Ninja
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```
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Build:
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```sh
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ninja -C build
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```
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## Test
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Full Unity output with colors:
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```sh
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ninja -C build check
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```
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CTest summary only:
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```sh
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ninja -C build test
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```
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`check` builds all suites and runs CTest with `--output-on-failure`,
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so assertion-level detail appears on any failure without running
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binaries by hand.
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## Coverage
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Configure with coverage instrumentation:
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```sh
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cmake -S . -B build-cov -G Ninja -DENABLE_COVERAGE=ON
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```
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Generate the HTML report:
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```sh
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ninja -C build-cov coverage
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```
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Open `build-cov/coverage/index.html` in a browser to view results.
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Only `celrs/` source files are measured. Unity, CMock, and generated
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mock files are excluded. Requires GCC or Clang with gcov support, and
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`gcovr` on `PATH`.
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> **Windows note:** requires GCC (e.g. `scoop install gcc`) or a Clang
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> build that includes compiler-rt. A custom Clang without compiler-rt
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> will fail at link time.
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## Architecture
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```
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celrs/
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crsf.h / crsf.c CRSF protocol: CRC8/DVB-S2, frame build/parse
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crsf_telemetry.h/.c Telemetry frame decoders (GPS, battery, link..)
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crsf_stream.h/.c Incremental streaming frame reader
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crsf_param.h/.c Parameter protocol (read/write/set_power)
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serial.h / serial.c Serial port abstraction (Win/POSIX)
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logger.h / logger.c Level-filtering logger
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log_write.h/.c stdout log sink
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tools/
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telemetry.c Telemetry read tool
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tests/
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test_crsf.c CRSF CRC, parse, build tests
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test_serial.c Serial open/close/stub tests
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test_logger.c Logger level-filtering tests
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deps/
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FindUnity.cmake Fetches Unity v2.6.1 via ZIP
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FindCMock.cmake Fetches CMock v2.6.0 via ZIP
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```
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## CRSF Protocol
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CRSF (Crossfire Serial Protocol) is the serial protocol used by ELRS for
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communication between ground station and TX/RX modules.
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### Frame format (ELRS USB CRSF)
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```
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+--------+----------+--------+----------+-----+
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| addr | length | type | payload | CRC |
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+--------+----------+--------+----------+-----+
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1 byte 1 byte 1 byte N bytes 1B
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```
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- **Address:** Frame sync byte (`0xC8` for host, `0xEE` for module, etc.)
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- **Length:** Total bytes after this field (type + payload + CRC)
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- **Type:** Frame type (RC channels, telemetry, parameter, etc.)
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- **Payload:** Frame-specific data
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- **CRC:** CRC8/DVB-S2 (poly `0xD5`) over type + payload
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### Common device addresses
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| Address | Device |
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| ------- | ----------------------------- |
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| 0x00 | FC Broadcast |
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| 0x10 | Flight Controller |
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| 0x80 | TBS Ground Station |
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| 0xEA | Custom Module (Radio) |
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| 0xEE | ELRS TX Module |
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| 0xEF | ELRS Lua (host script) |
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### Common frame types
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| Type | Name |
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| ------ | --------------------------- |
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| 0x01 | RC Channels Packed |
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| 0x02 | GPS |
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| 0x08 | Battery |
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| 0x0B | Heartbeat |
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| 0x14 | Link Stats |
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| 0x16 | RC Channels |
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| 0x28 | Device Ping |
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| 0x29 | Device Info |
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| 0x2B | Parameter Entry |
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| 0x2C | Parameter Read |
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| 0x2D | Parameter Write |
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| 0x2E | ELRS Status |
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