Date: Thu, 3 Feb 2011 17:26:25 +1030 From: "Daniel O'Connor" <doconnor@gsoft.com.au> To: Hans Petter Selasky <hselasky@c2i.net> Cc: freebsd-usb@freebsd.org Subject: Re: libusb performance on 8.1 Message-ID: <0F80A010-B97C-4D05-B604-5EF4B07EF248@gsoft.com.au> In-Reply-To: <201101280858.05077.hselasky@c2i.net> References: <9CF6C32F-E230-446B-94FC-C57F0F02B0E4@gsoft.com.au> <201101221433.23194.hselasky@c2i.net> <6AD22899-0B00-483D-A01E-786029A82C9F@gsoft.com.au> <201101280858.05077.hselasky@c2i.net>
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On 28/01/2011, at 18:28, Hans Petter Selasky wrote: > For this kind of applications ISOCHRONOUS transfers should be used. = Then you=20 > can have a double buffer guard in the range 1-56ms, regardless of the = buffer=20 > 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. 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.=20 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. Thanks :) =20 -- Daniel O'Connor software and network engineer for Genesis Software - http://www.gsoft.com.au "The nice thing about standards is that there are so many of them to choose from." -- Andrew Tanenbaum GPG Fingerprint - 5596 B766 97C0 0E94 4347 295E E593 DC20 7B3F CE8C
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