Date: Mon, 2 Jan 2012 19:29:56 +0100 From: Hans Petter Selasky <hselasky@c2i.net> To: freebsd-multimedia@freebsd.org Cc: Clemens Ladisch <clemens@ladisch.de> Subject: Re: M-Audio Oxygen 49: snd_uaudio cycles (loads, detaches, loads.... ad infinitum) Message-ID: <201201021929.56997.hselasky@c2i.net> In-Reply-To: <201201021902.16849.hselasky@c2i.net> References: <1325263531.4997.4.camel@localhost> <4F01CC65.2070408@ladisch.de> <201201021902.16849.hselasky@c2i.net>
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On Monday 02 January 2012 19:02:16 Hans Petter Selasky wrote: > On Monday 02 January 2012 16:25:25 Clemens Ladisch wrote: > > Hans Petter Selasky wrote: > > > It looks like your device has a problem with the clear-stall of the > > > BULK endpoint used for MIDI. In other words it is not fully USB > > > compliant. > > > > After devices whose descriptors were so broken that they couldn't ever > > run with newer Windows versions, after devices where (only!) the capture > > interface used big-endian samples, and after devices that corrupted > > their data buffer when receiving MIDI data with running status, I'm > > *extremely* surprised that there would be another M-Audio device with > > firmware bugs. > > > > > I'm not sure how we can avoid this. > > > > Plain MIDI does not have any error detection, so there is no error > > condition that could be reported with a stall. I've never seen > > a stalled MIDI endpoint, except for devices with broken hardware where > > the endpoint was stalled from the beginning and where a clear-stall > > wouldn't help. > > > > The Linux driver neither detects nor clears stalls, and works fine. > > > > It's obvious that clear-stall requests are not well tested in MIDI > > devices' firmwares, so I wouldn't be surprised if there were other > > devices that have the same bug, or even lock up. > > > > Is there a reason that umidi_probe/_open unconditionally issue clear- > > stalls, other than "just to be safe"? > > The reason is just to clear any buffered data from previous transfers. We > could probably skip this. Or make it optional via a sysctl. Though is clearly a violation of the USB specification, which mandates which requests are mandatory. --HPS
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