TS-4900 CAN: Difference between revisions

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#data 2 = 0x0c
#data 2 = 0x0c
cansend can0 -i 0x7Df 0x3 0x1 0x0c
cansend can0 -i 0x7Df 0x3 0x1 0x0c
## Some versions of cansend use a different syntax.  If the above
## commands gives an error, try this instead:
#cansend can0 7Df#03010c
</source>
</source>



Revision as of 13:05, 5 October 2015

The i.MX6 includes 2 CAN controllers which support the SocketCAN interface. Before proceeding with the examples, see the Kernel's CAN documentation here.

This board comes preinstalled with can-utils which can be used to communicate over a CAN network without writing any code. The candump utility can be used to dump all data on the network

## First, set the baud rate and bring up the device:
ip link set can0 type can bitrate 250000
ip link set can0 up

## Dump data & errors:
candump can0 &

## Send the packet with:
#can_id = 0x7df
#data 0 = 0x3
#data 1 = 0x1
#data 2 = 0x0c
cansend can0 -i 0x7Df 0x3 0x1 0x0c
## Some versions of cansend use a different syntax.  If the above
## commands gives an error, try this instead:
#cansend can0 7Df#03010c

This example packet is designed to work with the Ozen Elektronik myOByDic 1610 ECU simulator to read the RPM speed. This device will return data from candump with:

 <0x7e8> [8] 04 41 0c 60 40 00 00 00 
 <0x7e9> [8] 04 41 0c 60 40 00 00 00 

In this case, columns 6 and 7 are the current RPM value. This shows a simple way you can prove out the communication before moving to another language, but this next example sends the same packet and parses the same response in C:

#include <stdio.h>
#include <pthread.h>
#include <net/if.h>
#include <string.h>
#include <unistd.h>
#include <net/if.h>
#include <sys/ioctl.h>
#include <assert.h>
#include <linux/can.h>
#include <linux/can/raw.h>

int main(void)
{
	int s;
	int nbytes;
	struct sockaddr_can addr;
	struct can_frame frame;
	struct ifreq ifr;
	struct iovec iov;
	struct msghdr msg;
	char ctrlmsg[CMSG_SPACE(sizeof(struct timeval)) + CMSG_SPACE(sizeof(__u32))];
	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;
 
	if(bind(s, (struct sockaddr *)&addr, sizeof(addr)) < 0) {
		perror("socket");
		return -2;
	}
 
 	/* For the ozen myOByDic 1610 this requests the RPM guage */
	frame.can_id  = 0x7df;
	frame.can_dlc = 3;
	frame.data[0] = 3;
	frame.data[1] = 1;
	frame.data[2] = 0x0c;
 
	nbytes = write(s, &frame, sizeof(struct can_frame));
	if(nbytes < 0) {
		perror("write");
		return -3;
	}

	iov.iov_base = &frame;
	msg.msg_name = &addr;
	msg.msg_iov = &iov;
	msg.msg_iovlen = 1;
	msg.msg_control = &ctrlmsg;
	iov.iov_len = sizeof(frame);
	msg.msg_namelen = sizeof(struct sockaddr_can);
	msg.msg_controllen = sizeof(ctrlmsg);  
	msg.msg_flags = 0;

	do {
		nbytes = recvmsg(s, &msg, 0);
		if (nbytes < 0) {
			perror("read");
			return -4;
		}

		if (nbytes < (int)sizeof(struct can_frame)) {
			fprintf(stderr, "read: incomplete CAN frame\n");
		}
	} while(nbytes == 0);

	if(frame.data[0] == 0x4)
		printf("RPM at %d of 255\n", frame.data[3]);
 
	return 0;
}

Other languages have bindings to access CAN such as Python using C-types, Java using JNI.