Date: Thu, 3 Feb 2011 08:22:49 +0100 From: Hans Petter Selasky <hselasky@c2i.net> To: "Daniel O'Connor" <doconnor@gsoft.com.au> Cc: freebsd-usb@freebsd.org Subject: Re: libusb performance on 8.1 Message-ID: <201102030822.49266.hselasky@c2i.net> In-Reply-To: <0F80A010-B97C-4D05-B604-5EF4B07EF248@gsoft.com.au> References: <9CF6C32F-E230-446B-94FC-C57F0F02B0E4@gsoft.com.au> <201101280858.05077.hselasky@c2i.net> <0F80A010-B97C-4D05-B604-5EF4B07EF248@gsoft.com.au>
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On Thursday 03 February 2011 07:56:25 Daniel O'Connor wrote: > On 28/01/2011, at 18:28, Hans Petter Selasky wrote: > > For this kind of applications ISOCHRONOUS transfers should be used. Then > > you can have a double buffer guard in the range 1-56ms, regardless of > > the buffer size the hardware uses. > > That sounds nice :) > I am trying to get it working at the moment, however I'm only finding it > capable of 4 or 8 Mb/sec (512 or 1024 byte EP), although perhaps I don't > understand how to do ISO transfer properly. Hi, You need to set the multiplier to 2 or 3. Then you get 3*1024 bytes at maximum. > > BTW do you have a feel for the latency in bulk vs iso? I currently have > 5-10 msec of buffering in the hardware which I plan on increasing but I'm > not sure what a reasonable amount would be :) > > I put a logic analyser on my board and it shows fairly regular requests > from the hardware (16kbyte bursts every 2msec or so) however I see > glitches occasionally - 5.5ms, 7.5ms. > > I am not sure if they are attributable to userland scheduling (in which > case writing a kernel driver should help) or some subtlety in USB itself. Are you using two isochronous transfers or just one? --HPS
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