Luca
c32c4645b5
Tooling and findings for running an E8x/E9x electric power steering unit
outside its donor car, e.g. in an EV conversion.
Headline result: the EPS needs only two CAN messages plus a 12V enable
wire, not the 69-message set the car puts on the bus:
0x130 CAS terminal status (100ms) brings the unit up
0x1A0 DSC road speed (20ms) sets the assist level
Total required rate is 60 frames/s. Protocol write-up, including what is
proven vs. inferred and the open questions, is in eps-comms/.
Contents:
adapters/ CANdapter (its SLCAN dialect differs) and generic SLCAN
gateway/ car<->EPS relay, replay, message bench, EPS controller,
4-tab Streamlit UI
decoder/ PT-CAN frame decoding and live/replay sources
can-io/ XIAO ESP32-S3 firmware: CAN IO board + USB-CAN bridge with
a CAN-independent digital IO channel
tools/ capture, bitrate scan, startup-order and session analysis,
checksum solver
captures/ reference working session + the replay set eps_control reads
87 lines
3.3 KiB
Python
87 lines
3.3 KiB
Python
"""Scan common automotive CAN bitrates to find one that yields valid frames.
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Usage:
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python scan_bitrate.py [--port /dev/cu.usbserial-DNBJV4F5] [--seconds 2]
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Tries each candidate bitrate in turn, listens briefly, and reports how many
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frames came back and whether they look well-formed (DLC 0-8, plausible IDs).
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The bitrate with the most valid frames is your best bet.
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Note on wiring: CAN H and L being swapped is NOT usually something a bitrate
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scan can "see through" - CAN transceivers work on the differential voltage
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(H minus L), so swapping the two wires inverts dominant/recessive and
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corrupts every bit, at every bitrate. If this scan finds zero valid frames
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at all common bitrates, that's a strong signal to double check H/L wiring
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(and termination - a CAN bus needs ~120 ohm resistors at each end) rather
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than trying more bitrates.
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"""
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import argparse
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import sys
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import time
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from collections import Counter
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from pathlib import Path
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sys.path.insert(0, str(Path(__file__).resolve().parents[1]))
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from adapters.candapter import Candapter # noqa: E402
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DEFAULT_PORT = "/dev/cu.usbserial-DNBJV4F5"
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# Common automotive bitrates, most-likely-first for a steering/body bus.
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CANDIDATE_BITRATES = [500_000, 125_000, 250_000, 1_000_000, 100_000, 50_000, 20_000, 10_000]
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def scan_one(port: str, bitrate: int, seconds: float) -> tuple[int, int, Counter]:
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total = 0
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valid = 0
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ids = Counter()
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with Candapter(port, bitrate) as adapter:
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deadline = time.monotonic() + seconds
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while time.monotonic() < deadline:
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frame = adapter.read_frame(timeout=0.2)
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if frame is None:
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continue
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total += 1
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if 0 <= len(frame.data) <= 8:
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valid += 1
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ids[frame.arbitration_id] += 1
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return total, valid, ids
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def main() -> int:
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parser = argparse.ArgumentParser(description=__doc__)
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parser.add_argument("--port", default=DEFAULT_PORT, help="Serial device path")
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parser.add_argument("--seconds", type=float, default=2.0, help="Listen time per bitrate")
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args = parser.parse_args()
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print(f"Scanning {args.port} across {len(CANDIDATE_BITRATES)} bitrates ({args.seconds}s each)...\n")
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print(f"{'bitrate':>10} {'frames':>7} {'valid':>6} {'unique ids':>10}")
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results = []
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for bitrate in CANDIDATE_BITRATES:
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try:
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total, valid, ids = scan_one(args.port, bitrate, args.seconds)
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except OSError as exc:
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print(f"{bitrate:>10} error opening port: {exc}")
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continue
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print(f"{bitrate:>10} {total:>7} {valid:>6} {len(ids):>10}")
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results.append((bitrate, valid, ids))
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results.sort(key=lambda r: r[1], reverse=True)
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best = results[0] if results else None
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if best and best[1] > 0:
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bitrate, valid, ids = best
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print(f"\nBest match: {bitrate} bps ({valid} valid frames, {len(ids)} unique IDs).")
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print("Top IDs seen:", ", ".join(f"0x{i:X}x{c}" for i, c in ids.most_common(10)))
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else:
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print(
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"\nNo valid frames at any bitrate. Since this affects every bitrate equally, "
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"check the physical connection first: CAN H/L polarity and bus termination "
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"(~120 ohm at each end) before trying more bitrates."
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)
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return 0
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if __name__ == "__main__":
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raise SystemExit(main())
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