Date: Mon, 27 Jun 2011 10:43:03 +0200 From: Luca Pizzamiglio <l.pizzamiglio@bally-wulff.de> To: freebsd-usb@freebsd.org Subject: Read from bulk end point Message-ID: <4E084297.2040200@bally-wulff.de>
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Hi USB list, I've a little problem, but I'm not able to find a solution... I've a generic custom USB device with several end points. One of them (a bulk one) is read periodically (polled, 64 byte) every second. There was some time inconsistencies, so I checked the USB traffic with a sniffer, and I discovered that transactions are compacted at the start of the loop in a block of 64 read (64 byte * 64 msg = 4096 byte). In other words, on the bus the first read is followed immediately by the next 63 read. I guess that this is a pre-fetch optimization for BULK end points. How can I disable this optimization for this end point? How can I come back to a more "real-time" behavior? I tried to play with open() flags (O_NONBLOCK, O_DIRECT) without luck. Using FreeBSD 7 with HPS stack, this behavior didn't happen. Every read consists in 1 read on the bus and everything is fine. Thanks in advance! Luca
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