racegrade_tc8
Overview
racegrade_tc8 decodes a RaceGrade TC8 thermocouple amplifier’s CAN frames into two typed telemetry topics: its inputs (eight voltages, eight thermocouple temperatures, four frequencies) and its diagnostics. The TC8 transmits in the MoTeC E888 expander format, so the node uses the generated parser for dbcs/motec/Motec_E888_Rev1.dbc. It reads the raw frames can_bridge publishes and needs can_bridge running with the TC8 on its can0 channel. It does not configure the device: the one service it offers is a placeholder that acknowledges and sends nothing.
Running it
The node takes command-line options only; there is no configuration file. The frame topic and the output topics are fixed in the source.
./build/nodes/racegrade_tc8/racegrade_tc8
| Option | Meaning |
|---|---|
-s, --source | Zenoh key carrying CAN frames (default vehicle/can0/rx) |
-p, --prefix | Key prefix for this node’s topics (default nodes/racegrade_tc8) |
--debug | Debug logging |
-h, --help | Print usage and exit |
Running without hardware
mock_racegrade_tc8_frames under mock_data/ publishes a full cycle of the five Inputs pages every 75 ms or so, with every channel tracing a sine wave, on the topic the node reads.
./build/mock_data/mock_racegrade_tc8_frames # -k to use another key
./build/nodes/racegrade_tc8/racegrade_tc8 &
./build/nodes/inspect/inspect echo nodes/racegrade_tc8/inputs -n 3
The mock sends no Diagnostics frames, so diagnostics stays silent under it. test_racegrade_tc8_query, built next to the node, calls the placeholder service once and prints the reply.
Topics
| Topic | Schema | Contents |
|---|---|---|
nodes/racegrade_tc8/inputs | RaceGradeTc8Inputs | voltage1..8 in V, temperature1..8 in C, frequency1..4 in Hz |
nodes/racegrade_tc8/diagnostics | RaceGradeTc8Diagnostics | Two cold-junction compensation temperatures, internal temperature, six digital input states, battery volts, status flags, firmware version |
The node subscribes to vehicle/can0/rx with schema CanFrame and decodes two ids:
| CAN id | Message | Pages |
|---|---|---|
240 (0x0F0) | Inputs | Five, selected by the top three bits of byte 0: two voltages and two temperatures per page, with the frequencies on pages 3 and 4 |
241 (0x0F1) | Diagnostics | Three, selected by the top four bits of byte 0 |
A topic publishes once every page of its message has been seen since the last publish, so each sample holds one complete cycle. Temperatures are in quarter degrees on the wire and arrive here as C.
Health
The node publishes nodes/racegrade_tc8/health (NodeHealth) once a second, and at once whenever a check changes:
| Check | Degraded when |
|---|---|
can_rx | no CAN frame of any kind has arrived for a second: the bus is quiet, or the node is subscribed to the wrong key |
decoded | frames are arriving but none of them has been one of this node’s messages for two seconds |
inspect health prints them. The node exits cleanly on SIGINT or SIGTERM, so a monitor reads a deliberate stop as exited rather than as a crash.
Services
| Key | Request | Response |
|---|---|---|
nodes/racegrade_tc8/configure | RaceGradeTc8ConfigureRequest | RaceGradeTc8ConfigureResponse |
The request names a message format (e888Id0x0F0 to e888Id0x0FC, or a user-selectable output in temperature or millivolts), a transmit rate from 50 Hz down to once a minute, and a CAN id. As of 2026-09-14 the handler logs those three fields and replies response: true without transmitting anything to the TC8, so calling it changes nothing on the device.
Tests
ctest --test-dir build -L racegrade_tc8
| Target | Labels | Proves |
|---|---|---|
racegrade_tc8_test_messages | racegrade_tc8 unit | Eight voltages, eight thermocouples and four frequencies, each given a value nothing else has: the numbers themselves cannot say which channel they came from. |
The mapping lives in its own library (racegrade_tc8_messages.h) so it can be tested without a bus: the generated decoder is checked against cantools and the schema round-trips itself, but the wiring between the two is only checked here.
Troubleshooting
Both topics are advertised and neither publishes. inspect hz vehicle/can0/rx first: no frames means can_bridge is not running, or the TC8 is on a channel whose topic is not vehicle/can0/rx, and this node cannot be redirected. Frames arriving but none on 240 or 241 means the TC8 is set to another E888 base. The format enum in the service request lists 0x0F4, 0x0F8 and 0x0FC as alternatives the device supports; only 0x0F0 and 0x0F1 are decoded here.
inputs publishes and diagnostics never does. Under the mock that is expected. On hardware it means no 0x0F1 frames, or not all three of its pages: inspect echo vehicle/can0/rx -n 50 and look for id 241 with byte 0 cycling through 0x00, 0x10, 0x20.
The bus is empty and vehicle/can/status shows error counters climbing. A bit-rate mismatch presents as silence, not as bad values. can_bridge’s shipped config runs can0 at 500 kbit/s; MoTeC-format devices commonly run at 1 Mbit/s.
A temperature channel reads a large constant. An open thermocouple is reported by the device, not by this node; compare the cold-junction values in diagnostics, which should be near ambient, to tell a device fault from a wiring one.