Date: Mon, 27 Jun 2011 13:14:55 +0200 From: Luca Pizzamiglio <l.pizzamiglio@bally-wulff.de> To: Hans Petter Selasky <hselasky@c2i.net> Cc: freebsd-usb@freebsd.org Subject: Re: Read from bulk end point Message-ID: <4E08662F.7000401@bally-wulff.de> In-Reply-To: <201106271119.51079.hselasky@c2i.net> References: <4E084297.2040200@bally-wulff.de> <201106271119.51079.hselasky@c2i.net>
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Hi, thanks HPS, yes, the buffer size works well. It was strange, because for other endpoints I don't see this kind of behavior. BTW now the problem is solved. Thanks again Luca On 06/27/11 11:19, Hans Petter Selasky wrote: > On Monday 27 June 2011 10:43:03 Luca Pizzamiglio wrote: >> 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 > > There is an IOCTL to set the RX and TX buffer sizes. Please use that. See > dev/usb/usb_ioctl.h. The default is more than one full packet. > > --HPS
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