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Setup

I have two nodes connected to one CAN bus. The first node is a black-box, controlled by some real-time hardware. The second node is a Linux machine with attached PEAK-USB CAN controller:

+--------+               +----------+
| HW CAN |--- CAN BUS ---| Linux PC |
+--------+               +----------+

In order to investigate some problem related to occasional frame loss I want to mimic the CAN arbitration process. To do that I am setting the CAN bit-rate to 125Kb/s and flooding it with random CAN frames with 1ms delay, controlling the bus load with canbusload from can-utils. I also monitor CAN error frames running candump can0,0~0,#ffffffff and the overall can statistics with ip -s -d link show can:

26: can0: <NOARP,UP,LOWER_UP,ECHO> mtu 16 qdisc pfifo_fast state UNKNOWN mode DEFAULT group default qlen 10
    link/can  promiscuity 0
    can state ERROR-ACTIVE restart-ms 0
          bitrate 125000 sample-point 0.875
          tq 500 prop-seg 6 phase-seg1 7 phase-seg2 2 sjw 1
          pcan_usb: tseg1 1..16 tseg2 1..8 sjw 1..4 brp 1..64 brp-inc 1
          clock 8000000
          re-started bus-errors arbit-lost error-warn error-pass bus-off
          0          0          0          0          0          0
    RX: bytes  packets  errors  dropped overrun mcast
    120880     15110    0       0       0       0
    TX: bytes  packets  errors  dropped carrier collsns
    234123     123412   0       0       0       0

Problem

Now the problem is that the given setup works for hours with zero collisions (arbitration) or any other kind of error frames when the load is at 99%. When I reduce the delay to increase the bus load write(2) fails with either "ENOBUFS 105 No buffer space available" or "EAGAIN 11 Resource temporarily unavailable" - the actual error depends on whether I modify the qlen parameter or set to to defaults.

As I understand it, the load I put is either not enough or too much. What would be the right way to make two nodes enter the arbitration? A successful result would be a received CAN error frame corresponding to the CAN_ERR_LOSTARB constant from can/error.h and a value of collsns other than 0.

Source code

HW Node (Arduino Due with CAN board)

#include <due_can.h>

CAN_FRAME input, output;

// the setup function runs once when you press reset or power the board
void setup() {
  Serial.begin(9600);
  Serial.println("start");

//  Can0.begin(CAN_BPS_10K);
  Can0.begin(CAN_BPS_125K);
//  Can0.begin(CAN_BPS_250K);


  output.id = 0x303;
  output.length = 8;
  output.data.low = 0x12abcdef;
  output.data.high = 0x24abcdef;
}

// the loop function runs over and over again forever
void loop() {    
    Can0.sendFrame(output);
    Can0.read(input);

    delay(1);
}

Linux node

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>

#include <net/if.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/ioctl.h>

#include <linux/can.h>
#include <linux/can/raw.h>

int main(int argc, char *argv[])
{
  int s;
  int nbytes;
  struct sockaddr_can addr;
  struct can_frame frame;
  struct ifreq ifr;

  const char *ifname = "can0";

  if((s = socket(PF_CAN, SOCK_RAW, CAN_RAW)) < 0) {
    perror("Error while opening socket");
    return -1;
  }

  strcpy(ifr.ifr_name, ifname);
  ioctl(s, SIOCGIFINDEX, &ifr);

  addr.can_family  = AF_CAN;
  addr.can_ifindex = ifr.ifr_ifindex;

  printf("%s at index %d\n", ifname, ifr.ifr_ifindex);

  if(bind(s, (struct sockaddr *)&addr, sizeof(addr)) < 0) {
    perror("Error in socket bind");
    return -2;
  }

  frame.can_id  = 0x304;
  frame.can_dlc = 2;
  frame.data[0] = 0x11;
  frame.data[1] = 0x22;

  int sleep_ms = atoi(argv[1]) * 1000;

  for (;;) {
    nbytes = write(s, &frame, sizeof(struct can_frame));
    if (nbytes == -1) {
      perror("write");
      return 1;
    }
    usleep(sleep_ms);
  }
  return 0;
}
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1 回答 1

2

从文档小节 4.1.2 RAW 套接字选项 CAN_RAW_ERR_FILTER 中，它说错误默认情况下未激活，这就是丢失的仲裁字段ip没有增加的原因。

为了切换所有错误，您需要添加这两行：

can_err_mask_t err_mask = CAN_ERR_MASK;
setsockopt(socket_can, SOL_CAN_RAW, CAN_RAW_ERR_FILTER, &err_mask, sizeof(err_mask));

但此功能并非适用于所有驱动程序和设备，因为它要求硬件具有环回模式。在 PEAK-USB 的情况下，如果设备的固件版本低于 4.x，则似乎没有环回 [来源]。因此 SocketCAN 将无法检测丢失的仲裁。

于 2019-07-19T08:26:59.550 回答