Hi Christopher, On Monday 11 February 2008, Christopher Harvey wrote: > Hello, > I sent this to the video 4 linux mailing list earlier, but perhaps it's > more appropriate here since the code is very uvc specific.
Actually the bug is in your application, so it's not UVC specific :-) > I've created a small c program that uses pure v4l2 code to read from a > webcam on a uvc driver then copy that data into an SDL overlay. I've > posted the code here: > http://basementcode.com/serverMain.html > and I've attached a log file I created from the output of that program. > Overall the program works great except that after a few frames, about 35 > (varies each run) in my case, the select() function that is supposed to > block until new data from the webcam is available stops working and > returns right away. This isn't a huge problem because the following > ioctl(fd, VIDIOC_DQBUF, &buf) > call simply fails and sets errno to EAGAIN, then my app simply tries > again and again until it works. I'd rather select worked for the entire > duration of the capture to save cpu time and make sure that I read the > frame asap each time. The relevant function in the code I posted above > is "mainLoop", however I can't be sure the error is actually in that > function. I hope I've posted enough information. Your error is here: timeout.tv_sec = 2; timeout.tv_usec = 0; for(i = 0;i<200;i++) { FD_ZERO(&fds); FD_SET(fd, &fds); if(select(fd+1, &fds, NULL, NULL, &timeout)==-1) { printf("Error with select.\n"); break; } select() modifies the timeout parameter to return the remaining time. Your application will see timeout slowly decrementing until it reaches 0. select() will then always return immediately. You must reinitialise timeout in the for loop. Best regards, Laurent Pinchart _______________________________________________ Linux-uvc-devel mailing list [email protected] https://lists.berlios.de/mailman/listinfo/linux-uvc-devel
