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). [1] http://www.amazon.com/Syba-SD-CM-UAUD-Adapter-C-Media-Chipset/dp/B001MSS6CS [2] http://wiki.openwrt.org/toh/tp-link/tl-mr3020 -- 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
