Re: submit urb question (isochronous mode)
Alan Stern <[email protected]>
| Newsgroups | gmane.linux.usb.user |
|---|---|
| Message-ID | <[email protected]> |
On Mon, 10 Sep 2007, Philip Rakity wrote: > I am trying to understand the difference of the following: > > video camera -- isochronous mode --- data only comes into the HOST > > polling is done every 1ms > > > Now for the question > > I submit say > 10 urbs each with 10 buffers > > or > > I submit say > > 100 urb's with 1 buffer each > > assume that each buffer is big enough to hold the video frame that is > received by the host. Okay... but the maximum size of a full-speed isochronous transfer is only 1023 bytes. Is that really large enough to hold a video frame? > so what is the compare and contrast -- > > I guess that if every buffer is filled each 1ms then my callback is > called every 1ms for the 100 urb case and every 10ms for the 10urb case That's right. > anything else ? The CPU has more interrupt overhead in the 100-URB case, because it gets interrupted every ms. In the 10-URB case, interrupts occur every 10 ms. There's more general processing overhead in the 100-URB case, simply because it takes a certain amount of work to submit each URB -- and the amount of work needed for a 10-buffer URB is less than 10 times the work needed for a 1-buffer URB. Alan Stern ------------------------------------------------------------------------- This SF.net email is sponsored by: Microsoft Defy all challenges. Microsoft(R) Visual Studio 2005. http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/ _______________________________________________ [email protected] To unsubscribe, use the last form field at: https://lists.sourceforge.net/lists/listinfo/linux-usb-users