Dear Alan, We have questions: We still do not get unstanding about :why we get -FEBIG error when uvc driver re-submit urb yet. Because we try to use another platform that CPU is faster. The error is still occur. And,the amount of URB is 5 totally. the another platform : CPU 620MHz, RAM 64MB if each urb must use 5 iTDs, then totally 25 iTDs will be occupied in schedule list. The max schedule list is also large enough for that. And the new urb will be submit when the previous urb had complete. it is strange why urb submit is too late: in iso_stream_schedule() start - now is negative Do you have idea? About the precision of timestamp that I post from usbmon. the precision is in microsecond, do you mean nano is needed, right? Thanks a lot! best Regards, soho 2011/6/1 Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>: > On Tue, 31 May 2011, Soho Soho123 wrote: > >> Dear Alan, >> >> Thanks a lot for your comments! >> In advance, we have further question about scan_periodic(). we can see >> several time for "restart" label. The count is about 11 ~ 23. As your >> comment, "it should run only twice" ===> does it mean: the first time >> "modified" is true, then goto restart, in 2nd, "modified" is false >> (all of itd has complete), then go next, right? >> So, we can see the cpu cycle is very much when the count of restart is >> increase. Do you have idea about this phenomenon? > > The big "for" loop iterates through microframes. In your test, each > URB has 32 usb_iso_packet_descriptor structures and the interval is 1 > microframe, which means the URB will take 32 microframes (or 4 frames) > to execute. Each iTD can hold 8 transfer descriptions, but since the > transfers don't start at a frame boundary, each URB must use 5 iTDs. > > There should be an interrupt every time an URB completes, that is, > every 4 ms. While processing this interrupt, the Q_TYPE_ITD code will > run approximately 40 times and itd_complete() will be called 5 times. > But itd_complete() will return True for only one of those calls, the > call that corresponds to the last transfer of the URB. This means the > "goto restart" statement should be executed only once per interrupt, > and the "restart" line itself should be executed about 41 times per > interrupt. > > The uvcvideo callback is invoked when itd_complete() returns True. > That's when most of the CPU time should be used up. > > Are there high-precision timestamps available on your platform? The > usbmon output you posted did not have high-precision timestamps. > > Alan Stern > > -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
