On Mon, Feb 18, 2002 at 06:58:28PM -0500, Roland King wrote: > This is a little similar to the discussion we were having last > week about how to do interrupt transfers on the usbdevfs > interface. The answer seemed to end up being that you should > just do bulk transfers. > > I have read the USB spec several times now and see that there > are 4 sorts of endpoint and assumed that they required different > calls into the hardware to use them. Is that infact not the case? > > What is an interrupt transfer really? Is it just a transfer which is > sent again and again by the driver, or do you submit an interrupt > transfer to the hardware as an interrupt and it actually interrupts > you (hardware interrupt) on a regular basis? I initially thought it > was the latter, I'm now starting to think think that it's the former > and it's the driver which continually resubmits the transfer every > <interrupt period>. > > How is that supposed to work with output transfers then? If you > schedule an interrupt transfer and the driver continues to resubmit > it, doesn't that just mean that, as the initial writer in this thread > noted, you get the same data sent to the endpoint again and again? > What are interrupt outputs supposed to do? If you have just one > thing to send are you better off always just sending a bulk one even > to an interrupt endpoint?
As far as I know the only difference between one-shot out interrupt and an out bulk is that the interrupt should have guaranteed bandwidth - the USB core should allocate enough bandwidth on the bus to allow it to go through immediately or fail with a 'not enough bandwidth' error if it isn't possible. With bulk it simply waits until the bandwidth is available and then sends it. -- Vojtech Pavlik SuSE Labs _______________________________________________ [EMAIL PROTECTED] To unsubscribe, use the last form field at: https://lists.sourceforge.net/lists/listinfo/linux-usb-devel
