Error Detection & Fault Confinement

/* Read TEC/REC from CAN controller registers (STM32 example) */
#include "stm32f4xx_hal.h"

typedef struct {
    uint8_t  TEC;        /* Transmit Error Counter */
    uint8_t  REC;        /* Receive Error Counter */
    uint8_t  state;      /* 0=Active, 1=Passive, 2=BusOff */
} CAN_ErrorStatus_t;

CAN_ErrorStatus_t CAN_GetErrorStatus(CAN_HandleTypeDef* hcan)
{
    CAN_ErrorStatus_t status;
    uint32_t esr = hcan->Instance->ESR;

    /* TEC = bits [31:24], REC = bits [23:16] */
    status.TEC = (uint8_t)((esr >> 24) & 0xFF);
    status.REC = (uint8_t)((esr >> 16) & 0xFF);

    /* State from EPVF (Error Passive) and BOFF (Bus Off) flags */
    if (esr & CAN_ESR_BOFF)       status.state = 2; /* Bus Off */
    else if (esr & CAN_ESR_EPVF)  status.state = 1; /* Error Passive */
    else                           status.state = 0; /* Error Active */

    return status;
}

/* Counter rules per ISO 11898-1: */
/* TEC: +8 on transmit error, -1 on successful transmit */
/* REC: +1 on receive error (but +8 if bit error during error flag) */
/*      -1 on successful receive (min 0) */

# CANalyzer CAPL equivalent: monitor TEC/REC via diagnostic message
# Most CAN controllers expose TEC/REC via proprietary CAN message or OBD service

# Using python-can to poll controller stats (Linux SocketCAN)
import can, time

bus = can.interface.Bus(channel='can0', bustype='socketcan')
notifier = can.Notifier(bus, [])

# Monitor for error frames (CANalyzer: Statistics window → Error Frames)
error_count = 0
start = time.time()

for msg in bus:
    if msg.is_error_frame:
        error_count += 1
        print(f"t={msg.timestamp-start:.3f}s ERROR FRAME #{error_count}")

    # Read TEC/REC from /sys/class/net/can0/statistics/
    with open('/sys/class/net/can0/statistics/bus_error') as f:
        bus_errors = int(f.read())
    with open('/sys/class/net/can0/statistics/error_passive') as f:
        passive_count = int(f.read())

    if passive_count > 0:
        print(f"WARNING: node entered Error Passive state ({passive_count} times)")
        # Investigate: faulty transceiver, EMC issue, baud rate mismatch