On Mon, 31 Dec 2012, Shawn Lewis wrote: > Hi list, I've been looking into an issue wherein a cheap usb sound > card [1] plugged into a host system with a 400MHz mips core [2] makes > audible popping noises, at a rate of up to a few times per second. I > don't believe the problem is at the application or alsa layers, as I > don't get underflow errors. > > I'm running a 3.3.8 kernel from openwrt. The usb host uses the ehci > driver. The sound card uses the snd-usb-audio driver. > > This only happens when the wifi built into the chip is enabled, and > wifi traffic is occuring. If I disable it there are no audible pops. A > different cheap usb sound card produces less pop noises, but it still > makes them. > > My theory is that the wifi processing throws off the timing for the > usb driver, so sometimes the isochronous schedule and data is not > updated in time for the next usb frame. My understanding of usb/ehci > is limited as I have only read the spec this weekend so I could be way > off base. I might also be having a hardware/electrical issue rather > than software/kernel. > > Any tips or advice appreciated. > > I can provide usbmon output for popping and non-popping cases. I also > have audio recordings, and usb analyzer traces. The analyzer trace > shows partial packets arriving during pops, with the rest arriving > 200us later. There were sometimes other errors as well (sorry I don't > have the analyzer trace on this machine). Yes, please provide the usbmon traces. Alan Stern -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
