Date: Thu, 2 May 2019 17:52:05 +0930 From: "O'Connor, Daniel" <darius@dons.net.au> To: Hans Petter Selasky <hps@selasky.org> Cc: freebsd-usb@freebsd.org Subject: Re: USB transfers in device drivers Message-ID: <D73B37BF-8C28-4EE4-8026-5E9BF8B5C4AD@dons.net.au> In-Reply-To: <af8dfb40-1d48-d03b-465f-32b4361e91c0@selasky.org> References: <3B922C60-32E5-484E-8AFA-28FF7255CF2C@dons.net.au> <af8dfb40-1d48-d03b-465f-32b4361e91c0@selasky.org>
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> 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? > 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). Related to bandwidth - are there any statistics gathered about how busy a port is? Thanks -- Daniel O'Connor "The nice thing about standards is that there are so many of them to choose from." -- Andrew Tanenbaumhome | help
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