CAN 통신 구현 — bxCAN·Filter·Mailbox·CAN-FD

1
CAN_H ────╲╱──────────────╲╱──
2
CAN_L ──── ╱╲──────────────╱╲──
3
        Dominant       Recessive
4
        (0)            (1)
5
        H>L            H=L

1
SOF | ID(11) | RTR | IDE | r0 | DLC(4) | DATA(0~8 byte) | CRC(15) | ACK | EOF
2
 │      │     │     │         │            │              │       │
3
 │   priority           data length        payload     receivers
4
 │                                                       ACK
5
START dominant bit

1
1 bit = 1 + tseg1 + tseg2 quanta
2
sample point at end of tseg1
3

4
baud = peripheral_clock / (prescaler × (1 + tseg1 + tseg2))
5

6
예) PCLK1 = 42 MHz, target 500 kbit/s
7
    prescaler = 6, tseg1 = 11, tseg2 = 2
8
    1 bit = (1 + 11 + 2) × 6 / 42M = 84 / 42M = 2 µs → 500 kHz
9
    sample point = (1 + 11) / 14 = 85.7% (CiA recommended 87.5%)

1
TEC (Transmit Error Counter):
2
  error 시 +8, 정상 송신 시 -1
3
  TEC ≥ 128 → Error Passive
4
  TEC ≥ 256 → Bus Off (송신 중단)
5

6
REC (Receive Error Counter):
7
  비슷, 수신 측
8

9
Bus-off → 128 × 11 recessive bit 후 자동 복구 (또는 수동)

1
void can_init_500k(void) {
2
    RCC->APB1ENR |= RCC_APB1ENR_CAN1EN;
3
    RCC->AHB1ENR |= RCC_AHB1ENR_GPIOAEN;
4

5
    // PA11 RX, PA12 TX (AF9)
6
    gpio_init(GPIOA, 11, &(gpio_config_t){.mode=GPIO_MODE_AF, .pull=GPIO_PULL_UP, .af=9});
7
    gpio_init(GPIOA, 12, &(gpio_config_t){.mode=GPIO_MODE_AF, .speed=GPIO_SPEED_HIGH, .af=9});
8

9
    // Enter init mode
10
    CAN1->MCR |= CAN_MCR_INRQ;
11
    while (!(CAN1->MSR & CAN_MSR_INAK));
12

13
    CAN1->MCR &= ~CAN_MCR_SLEEP;
14
    CAN1->MCR |= CAN_MCR_TXFP | CAN_MCR_NART;
15
    // TXFP = priority by request order
16
    // NART = no auto retransmit
17

18
    // 500 kbit/s @ PCLK1 = 42 MHz
19
    // prescaler 6, tseg1=11, tseg2=2 → (1+11+2)*6/42M = 2 µs
20
    CAN1->BTR = (1u << 24)            // SJW = 2
21
              | ((2 - 1) << 20)        // tseg2 = 2
22
              | ((11 - 1) << 16)       // tseg1 = 11
23
              | (6 - 1);               // prescaler = 6
24

25
    // Exit init mode
26
    CAN1->MCR &= ~CAN_MCR_INRQ;
27
    while (CAN1->MSR & CAN_MSR_INAK);
28
}

1
void can_filter_init(void) {
2
    CAN1->FMR |= CAN_FMR_FINIT;
3

4
    // Filter 0: accept ID 0x100 (11-bit, mask all bits)
5
    CAN1->FA1R &= ~(1u << 0);
6
    CAN1->FS1R |=  (1u << 0);    // 32-bit scale
7
    CAN1->FM1R &= ~(1u << 0);    // mask mode
8

9
    CAN1->sFilterRegister[0].FR1 = (0x100 << 21);    // filter ID
10
    CAN1->sFilterRegister[0].FR2 = (0x7FF << 21);    // mask: all 11 bits
11

12
    CAN1->FFA1R &= ~(1u << 0);   // assign to FIFO 0
13
    CAN1->FA1R  |=  (1u << 0);   // activate
14

15
    CAN1->FMR &= ~CAN_FMR_FINIT;
16
}
17

18
// 모든 ID 수신
19
void can_filter_pass_all(void) {
20
    CAN1->FMR |= CAN_FMR_FINIT;
21
    CAN1->FA1R &= ~(1u << 0);
22
    CAN1->FM1R &= ~(1u << 0);
23
    CAN1->FS1R |=  (1u << 0);
24
    CAN1->sFilterRegister[0].FR1 = 0;
25
    CAN1->sFilterRegister[0].FR2 = 0;   // mask = 0 → don't care
26
    CAN1->FA1R |= (1u << 0);
27
    CAN1->FMR &= ~CAN_FMR_FINIT;
28
}

1
int can_send(uint32_t id, const uint8_t *data, uint8_t len) {
2
    // 빈 mailbox 찾기
3
    int mb = -1;
4
    if      (CAN1->TSR & CAN_TSR_TME0) mb = 0;
5
    else if (CAN1->TSR & CAN_TSR_TME1) mb = 1;
6
    else if (CAN1->TSR & CAN_TSR_TME2) mb = 2;
7
    else return -1;
8

9
    CAN1->sTxMailBox[mb].TIR  = (id << 21);          // standard
10
    CAN1->sTxMailBox[mb].TDTR = len & 0xF;
11
    CAN1->sTxMailBox[mb].TDLR = (data[0])
12
                              | (data[1] << 8)
13
                              | (data[2] << 16)
14
                              | (data[3] << 24);
15
    CAN1->sTxMailBox[mb].TDHR = (data[4])
16
                              | (data[5] << 8)
17
                              | (data[6] << 16)
18
                              | (data[7] << 24);
19
    CAN1->sTxMailBox[mb].TIR |= CAN_TI0R_TXRQ;       // request transmit
20
    return 0;
21
}

1
typedef struct {
2
    uint32_t id;
3
    uint8_t  len;
4
    uint8_t  data[8];
5
} can_rx_t;
6

7
#define RX_Q 32
8
static volatile can_rx_t rx_q[RX_Q];
9
static volatile int rx_head, rx_tail;
10

11
void can_rx_init(void) {
12
    CAN1->IER |= CAN_IER_FMPIE0;        // FIFO0 message pending
13
    NVIC_EnableIRQ(CAN1_RX0_IRQn);
14
}
15

16
void CAN1_RX0_IRQHandler(void) {
17
    while (CAN1->RF0R & CAN_RF0R_FMP0) {
18
        can_rx_t f;
19
        f.id = CAN1->sFIFOMailBox[0].RIR >> 21;
20
        f.len = CAN1->sFIFOMailBox[0].RDTR & 0xF;
21
        uint32_t lo = CAN1->sFIFOMailBox[0].RDLR;
22
        uint32_t hi = CAN1->sFIFOMailBox[0].RDHR;
23
        f.data[0] = lo;  f.data[1] = lo >> 8;  f.data[2] = lo >> 16; f.data[3] = lo >> 24;
24
        f.data[4] = hi;  f.data[5] = hi >> 8;  f.data[6] = hi >> 16; f.data[7] = hi >> 24;
25
        CAN1->RF0R |= CAN_RF0R_RFOM0;   // release
26

27
        int next = (rx_head + 1) % RX_Q;
28
        if (next != rx_tail) {
29
            rx_q[rx_head] = f;
30
            rx_head = next;
31
        }
32
    }
33
}
34

35
int can_recv(can_rx_t *f) {
36
    if (rx_head == rx_tail) return -1;
37
    *f = rx_q[rx_tail];
38
    rx_tail = (rx_tail + 1) % RX_Q;
39
    return 0;
40
}

1
CAN1->MCR |= CAN_MCR_INRQ;
2
while (!(CAN1->MSR & CAN_MSR_INAK));
3
CAN1->BTR |= CAN_BTR_LBKM;   // loopback
4
CAN1->MCR &= ~CAN_MCR_INRQ;