Add baud rate probing (921600/400000/420000), auto-detect ELRS
ports, verify module responds to CRSF ping before telemetry loop,
and increase RC send rate to 50 Hz to match Python reference.
Telemetry tool now:
- Reads raw bytes from serial port
- Parses frames incrementally via cel_crsf_stream
- Decodes link stats, battery, heartbeat, airspeed
- Sends RC frames periodically to keep link alive
- Handles Ctrl+C gracefully via signal handler
The old [0xC8][dest][src][type][size][payload][crc] format was never
used with real hardware. Remove cel_crsf_frame_legacy, *_legacy()
functions, and update tests/tools accordingly.
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.
Drop timeout_ms; read now returns immediately with whatever
data is available (0 if none), so callers don't block the rest
of their loop waiting on serial I/O.
telemetry's poll loop now sleeps interval_ms itself between
empty reads via a small sleep_ms helper.
Implement cel_serial_list_ports/cel_serial_free_ports with
platform backends: Windows reads HKLM\HARDWARE\DEVICEMAP\
SERIALCOMM (fast, single registry read), POSIX scans /dev for
ttyUSB*/ttyACM*.
telemetry tool gains --list, --port, and --baudrate flags;
baud rate was previously hardcoded to 400000. Rename the
tool_telemetry CMake target to telemetry.
Fix test_free_ports_zero_count, which passed a stack array to
cel_serial_free_ports (which calls free() on it), corrupting
the heap.
portersky