can_sniffer.tc

CAN bus sniffer — empfängt alle Frames auf dem Bus und loggt sie

Source on GitHub

// CAN bus sniffer — empfängt alle Frames auf dem Bus und loggt sie
//
// Wiring (this example assumes ESP32-S3 with external CAN transceiver
// like SN65HVD230 / TJA1051 / MCP2562 between MCU and bus):
//   GPIO_TX → transceiver TXD (input)
//   GPIO_RX ← transceiver RXD (output)
//   Transceiver CANH/CANL → bus
//
// Default pin/bitrate matches Hans's bench rig where this device sits
// on the same bus as .143 (running slcan_bridge_tcp.tcb). Frames the
// PC sends over `192.168.188.143:9999` via SLCAN end up here.

int  rx_pin   = 39;       // ESP32-S3 .39 wiring 2026-05-16: RX=GPIO39 ← RXD, TX=GPIO38 → TXD
int  tx_pin   = 38;
int  bitrate  = 250;      // kbit/s — must match the other end
int  twai_mode = 0;       // 0 = NORMAL (ACK on bus), 1 = NO_ACK
                          // (self-test only — wrong here, we want bus ACK)

int  twai_open  = 0;
int  rx_total   = 0;      // lifetime received-frame counter
int  rx_meta[4];          // [0]=id, [1]=ext, [2]=dlc
int  rx_data[8];          // up to 8 payload bytes
int  last_id   = -1;
int  last_dlc  = 0;
int  last_ext  = 0;
int  last_data[8];

char  m[120];             // log + WebCall scratch
char  ext_str[4];         // "EXT" or "STD" — TinyC sprintf %s needs a char[]
                          // not a ternary-with-string-literals expression.

void open_bus() {
    if (twai_open) return;
    int rc = twaiBegin(rx_pin, tx_pin, bitrate, twai_mode);
    if (rc < 0) {
        sprintf(m, "CAN: twaiBegin(rx=%d,tx=%d,%d kbit/s,mode=%d) FAILED rc=%d",
                rx_pin, tx_pin, bitrate, twai_mode, rc);
        addLog(m);
        return;
    }
    twai_open = 1;
    sprintf(m, "CAN: bus opened rx=%d tx=%d %d kbit/s mode=%d",
            rx_pin, tx_pin, bitrate, twai_mode);
    addLog(m);
}

// Drain RX queue every tick. Tight loop with bounded count so a flood
// can't starve other callbacks. twaiRecv returns 0 when queue is empty
// (non-blocking), > 0 with bytes_read on a frame, < 0 on driver error.
void Every50ms() {
    if (!twai_open) return;
    int guard = 16;
    while (guard > 0) {
        int n = twaiRecv(rx_meta, rx_data, 8);
        if (n <= 0) break;
        rx_total = rx_total + 1;
        last_id   = rx_meta[0];
        last_ext  = rx_meta[1];
        last_dlc  = rx_meta[2];
        int i = 0;
        for (i = 0; i < 8; i = i + 1) {
            if (i < last_dlc) last_data[i] = rx_data[i]; else last_data[i] = 0;
        }
        if (last_ext) strcpy(ext_str, "EXT"); else strcpy(ext_str, "STD");
        addLog("CAN RX #%d  %s ID=0x%03x DLC=%d  %02x %02x %02x %02x %02x %02x %02x %02x", rx_total, ext_str, last_id, last_dlc, last_data[0], last_data[1], last_data[2], last_data[3], last_data[4], last_data[5], last_data[6], last_data[7]);
        guard = guard - 1;
    }
}

void EverySecond() {
    if (!twai_open) {
        open_bus();
    }
}

void WebCall() {
    char state[12];
    if (twai_open) strcpy(state, "open"); else strcpy(state, "closed");
    sprintf(m, "{s}CAN bus (RX=%d TX=%d @ %dkbit/s){m}%s{e}",
            rx_pin, tx_pin, bitrate, state);
    webSend(m);

    sprintf(m, "{s}Frames empfangen (lifetime){m}%d{e}", rx_total);
    webSend(m);

    if (rx_total > 0) {
        if (last_ext) strcpy(ext_str, "EXT"); else strcpy(ext_str, "STD");
        sprintf(m,
            "{s}Letzter Frame{m}%s ID=0x%03x DLC=%d{e}",
            ext_str, last_id, last_dlc);
        webSend(m);

        sprintf(m,
            "{s}Letzte Daten{m}%02x %02x %02x %02x %02x %02x %02x %02x{e}",
            last_data[0], last_data[1], last_data[2], last_data[3],
            last_data[4], last_data[5], last_data[6], last_data[7]);
        webSend(m);
    }
}

int main() {
    twai_open = 0;
    rx_total  = 0;
    last_id   = -1;
    open_bus();          // try once immediately; EverySecond retries on fail
    addLog("CAN sniffer: started");
    return 0;
}