net/can: can protocol uses a separate buffer to cache can data

[zhhyu7]

Summary

To avoid memory waste, can add support for using an independent iob buffer
The IP protocol often configures CONFIG_IOB_BUFSIZE to be relatively large,
such as 512, for higher throughput. However, the buffer required by CAN is
fixed at a length of 16 or 64. If the system's IOB is directly used,
a lot of memory will be wasted.

Impact

net/can and can device driver

Testing

qemu:local
test code:

#include <nuttx/can/can.h>
#include <nuttx/config.h>
#include <stdint.h>
#include <stdio.h>
#include <fcntl.h>
#include <unistd.h>

#define CAN_RCV_BUF_MAX 1024

void dump_can_msg(struct can_msg_s* msg, bool tx)
{
    if(tx)
      printf("---> TX: ");
    else
      printf("<--- RX: ");

    printf("ID 0x%02x, Data ", msg->cm_hdr.ch_id);
    for(int i=0;i<can_dlc2bytes(msg->cm_hdr.ch_dlc);i++)
    {
      printf(" 0x%02x ", msg->cm_data[i]);
    }
    printf("\n");
}

void build_tx_msg(struct can_msg_s* msg)
{
  static uint32_t echo_cnt = 0x120;
  memset(msg, 0, sizeof(struct can_msg_s));
  msg->cm_hdr.ch_id = 0x123;
  msg->cm_hdr.ch_dlc = 8;
  msg->cm_data[0] = echo_cnt & 0xff;
  msg->cm_data[1] = (echo_cnt >> 8) & 0xff; 

  echo_cnt++;
}

int main(int argc, FAR char *argv[])
{
  printf("Hello, World!!\n");
  char buf[CAN_RCV_BUF_MAX];
  int nbytes;
  int ret;
  struct can_msg_s* rxmsg;
  struct can_msg_s txmsg;

  int fd = open("/dev/can0", O_RDWR | O_CLOEXEC);
  if (fd < 0) {
    printf("open failed\n");
    return -1;
  }
  
  while(1)
  {
    sleep(1);
    build_tx_msg(&txmsg);
    dump_can_msg(&txmsg, true);
    ret = write(fd, &txmsg, sizeof(struct can_msg_s));
    if(ret < 0)
    {
      printf("write failed\n");
      return -1;
    }

    nbytes = read(fd, buf, CAN_RCV_BUF_MAX);
    if(nbytes < 0) 
    {
      printf("read failed\n");
      return -1;
    }
    rxmsg = (struct can_msg_s*)buf;
    dump_can_msg(rxmsg, false);    

  }
  close(fd);

  return 0;
}

test log:

NuttShell (NSH) NuttX-12.11.0
vela> hello
Hello, World!!
---> TX: ID 0x123, Data  0x20  0x01  0x00  0x00  0x00  0x00  0x00  0x00
<--- RX: ID 0x07, Data  0x20  0x01  0x00  0x00
...