Date: Mon, 12 Nov 2018 20:46:13 +0100 From: "Herbert J. Skuhra" <herbert@gojira.at> To: Hans Petter Selasky <hps@selasky.org> Cc: freebsd-arm@freebsd.org Subject: Re: Raspberry PI 2B/3 and USB audio Message-ID: <875zx2hyey.wl-herbert@gojira.at> In-Reply-To: <6beca923-ba25-3814-6bb2-f4cc2d7360d3@selasky.org> References: <87ftw96uq0.wl-herbert@gojira.at> <6beca923-ba25-3814-6bb2-f4cc2d7360d3@selasky.org>
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On Sun, 11 Nov 2018 13:52:14 +0100, Hans Petter Selasky wrote: > > On 11/10/18 12:24 PM, Herbert J. Skuhra wrote: > > Hi, > > > > if you use an USB sound card on your Raspberry PI 2B/3, can you please > > answer the following questions: > > > > - which USB sound card? > > - do you have bad audio on current or stable/12 after r339388? > > > > My "Creative Technology Ltd Sound Blaster Play 2" device sounds very > > bad. Meanwhile more changes were commited but they don't fix audio > > completly. > > > > Hi, > > Some background: > > The USB controller in Raspberry PI is running HIGH-speed USB. Many USB > audio device are FULL-speed USB. In order for a FULL-speed USB device > to work in a HIGH-speed USB environment all data transfers need to go > through a so-called transaction translator. This transaction > translator operate on chunks of data, 171 bytes maximum. That means if > a USB audio stream generates 1000 packets per second, then suddenly a > bunch of smaller packets will be needed. This puts some stress on the > DWC OTG driver and there might be some room for improvement in this > area too, but the basic sympthom is that the DWC OTG driver in FreeBSD > is not always able to keep up with the timing required for these > so-called split transactions. One idea is to move all DWC OTG IRQ > handling away from CPU-0. I'm not sure if cpuset supports this yet on > armv7 // arm64. Might have to be done in the driver. > > Further some audio device use non-adaptive clocks, which means the > recording channel must be active along with the playback channel else > jitter will occur. > > The recommendation for RPI is a HIGH-speed USB audio device (should be > clearly marked in the specification). Using a HIGH-speed USB audio > device will reduce the number of interrupts significantly. Well, the sound card worked perfectly fine so far... both on FreeBSD and Arch Linux ARM... no luck with NetBSD. Never mind! I am obviously the only user affected by this "fix" (r339388). -- Herbert
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