CODEWITHSUNDEEP
c++linuxserial-portusbusbserial
JonB55
JonB55

Reputation: 31

New to linux: C++ opening and closing usb port issues

New developer, Linux, C++, USB - Serial Adapter.

I've completed a program where I am able to write to the USB port. However, if I change my code, make, log back in as root, and try to write to the port again, it doesn't go through. It'll only work if I remove the USB cable from the computer and reseat it before attempting sending data again. If you need more info let me know.

I'm on two different computers and have no way of copying and pasting but here is the gist of what I'm doing.

int fd = 0;
int iOut = 0;
char *ComPort = "/dev/ttyUSB0";

fd=open(ComPort, O_CREAT | O_RDWR | O_NOCTTY | O_NDELAY);

if(fd == -1)
  cout << "unable to open" << endl;

// blah blah getting data ready to be sent
// create a block of 50 hex characters to be sent : DB

iOut = write(fd, $DB, sizeof(DB));

// blah blah error checking

close(fd);
return(0);

Upvotes: 1

Views: 1867

Answers (2)

JonB55
JonB55

Reputation: 31

@Surt @alexfarber I had a talk with a coworker on this and we concluded that this is most likely a hardware issue with my display or usb to serial adapter. I believe the only way this can work with this particular adapter is by turning off the power to it and turning it back on in order to reflect what it would see when being removed and reseated manually. I dont believe this is possible but I'll start another thread with anything I may run into. I appreciate you all taking the time to help with this, I did learn a number of other things I didn't know before hand so this was still very helpful. Thank you once again.

Upvotes: 2

Surt
Surt

Reputation: 16099

Take at look at chapter 3.2 here http://www.tldp.org/HOWTO/Serial-Programming-HOWTO/x115.html add some of the error checking first so you can see where if fails. The perror line will help there.

if (fd <0) {perror(ComPort ); exit(-1); } // note the exit which your code doesn't have.

This should now tell you some more info and add

if (errno) {perror(ComPort ); exit(-1); }

after all operations, read, write and set things on the fd.

now add the newtio part of 3.2 to your program in case some handshake failed. You must change it so it conforms with the display.

The final version of your program might be more like 3.3.

Upvotes: 1

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