On 30/08/15(Sun) 09:31, John L. Scarfone wrote: > On Sun, Aug 30, 2015 at 12:32:24PM +0200, Martin Pieuchot stated: > > That's good but the original design of allocating an xfer for every > > usbd_transfer(9) call does not make much sense. > > > > You could allocate two xfers (one for read and one for write) at the > > same time the pipes are opened and free them when they're closed. > > > > You could even allocate the DMA buffer with usb_alloc_buffer() and pass > > the USBD_NO_COPY flag to usbd_transfer(9) to avoid a supplementary copy. > > Thanks for the feedback, Martin. I've been running with your first > suggestion for a bit with no issues. I wonder though if the xfer can't > just be shared for rx and tx?
You cannot easily do that because the CPU executing usbd_transfer(9) with a USBD_SYNCHRONOUS flag might sleep. So if you try to submit another transfer at this moment using the same "xfer" descriptor bad things will happen ;) > I also NULLed out the pipes on failure > since it looks like otherwise they'd be re-closed on detach. I'll look > into the usbd_alloc_buffer() idea. That'd great, thanks. I've just committed your diff, good work.
