Sure. These are from playing a 100Hz sine wave tone over the USB sound card. This is with the wifi device disabled (meaning its not present in ifconfig's output, no wifi interrupts occur). No audible pops occurred in this sample. http://dl.dropbox.com/u/324766/usb-popping/usbmon-100Hz-nowifi.txt This is with the wifi device enabled (present in ifconfig's output, hundreds of wifi interrupts per second) and wifi traffic being generated by ping flooding. Audible pops occurred frequently (up to a few times per second) in this sample. http://dl.dropbox.com/u/324766/usb-popping/usbmon-100Hz-wifi.txt On Tue, Jan 1, 2013 at 7:03 AM, Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> wrote: > 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
