Date: Thu, 2 May 2019 10:36:52 +0200 From: Hans Petter Selasky <hps@selasky.org> To: "O'Connor, Daniel" <darius@dons.net.au> Cc: freebsd-usb@freebsd.org Subject: Re: USB transfers in device drivers Message-ID: <e4fdb075-faa8-7832-227b-89700e832162@selasky.org> In-Reply-To: <D73B37BF-8C28-4EE4-8026-5E9BF8B5C4AD@dons.net.au> References: <3B922C60-32E5-484E-8AFA-28FF7255CF2C@dons.net.au> <af8dfb40-1d48-d03b-465f-32b4361e91c0@selasky.org> <D73B37BF-8C28-4EE4-8026-5E9BF8B5C4AD@dons.net.au>
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On 2019-05-02 10:22, O'Connor, Daniel wrote: > > >> On 2 May 2019, at 06:15, Hans Petter Selasky <hps@selasky.org> wrote: >> On 2019-05-01 10:34, O'Connor, Daniel wrote: >>> I don't have a solid hypothesis for the failures as yes but one thing I'd like to make sure is that the USB stack is keeping the USB hardware busy with pending requests - does anyone know if the USB FIFO code does that automatically? >> >> Only the XHCI driver supports HW based double buffering of BULK transfers. > > Ahh interesting - is that a ECHI hardware limitation or a driver one? Hi, It is an EHCI hardware "limitation". It is possible to queue up more jobs with the EHCI, but it ends that you get a race with the hardware you'll need to catch. I think it is related to how receiving short packets are handled. > >> I suppose you are using BULK. Else you will need to use ISOCHRONOUS transfers. > > Yes it's using bulk transfers. > > I did consider isochronous transfers when I started this project but I wasn't sure if there would be enough bandwidth (but perhaps I read the spec wrong). I imagine there would be enough for this data rate but we have others at higher speeds (eg 35MB/sec). If you want reliable data transfer, BULK is the best. > > Related to bandwidth - are there any statistics gathered about how busy a port is? No, but I wanted to add a text-graph frontent to usbdump to collect this info realtime. Else use a USB wire-analyzer. --HPS
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