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How to detect unplugged PCAN-USB?
Posted: Mon 13. Jan 2020, 11:36
by Cluni
Hi,
I'm trying to use a PCAN-USB using SocketCAN in cpp under linux. Therefore I'm using a non-blocking read. Now I have the problem that I can't detect, if the PCAN-USB itself is unplugged out of the USB-Port. The read returns a -1 -- doesn't matter if the adapter is unplugged or if there only is a timeout. Is there a possibility to differ between these two situations?
Best regards,
Bernd
Re: How to detect unplugged PCAN-USB?
Posted: Mon 13. Jan 2020, 12:40
by M.Heidemann
Hi,
If you take a look at the source code for candump (Which you can find online by searching "candump.c"), you can see how this is handled in SocketCan (Starting from line 647):
Code: Select all
for (i=0; i<currmax; i++) { /* check all CAN RAW sockets */
if (FD_ISSET(s[i], &rdfs)) {
int idx;
/* these settings may be modified by recvmsg() */
iov.iov_len = sizeof(frame);
msg.msg_namelen = sizeof(addr);
msg.msg_controllen = sizeof(ctrlmsg);
msg.msg_flags = 0;
nbytes = recvmsg(s[i], &msg, 0);
idx = idx2dindex(addr.can_ifindex, s[i]);
if (nbytes < 0) {
if ((errno == ENETDOWN) && !down_causes_exit) {
fprintf(stderr, "%s: interface down\n", devname[idx]);
continue;
}
perror("read");
return 1;
}
You can take this as a starting point to implement your own solution.
Also take a look at the examples given in the documentation for SocketCan:
https://www.kernel.org/doc/Documentatio ... ng/can.txt
Best Regards
Marvin
Re: How to detect unplugged PCAN-USB?
Posted: Mon 13. Jan 2020, 14:49
by Cluni
Hello Marvin,
thank you very much!
was the right hint!
I already took a look at the file "candump.h" before, but unfortunately I had an other (older?) version of this file. There wasn't any use of errno...
Now it works like it should! Thanks a lot!
Best regards
Bernd