On Wed, 2 Jan 2013, Shawn Lewis wrote: > Am I understanding ehci correctly here? It looks like we only get an > interrupt every 8ms even though the isochronous period is 1ms. That's > because we can schedule 8 isochronous transactions at a time, meaning > the host controller hardware takes over for 8 milliseconds and > notifies the kernel via an interrupt only after the 8th transaction > completes. (basically I'm making sure I understand the division of > labor between hardware and software). Yes, that's more or less right. Of course, this isn't a property of EHCI itself but rather a result of the fact that the audio driver submits transfer requests containing 8 packets of data. (Actually a few of the requests have fewer than 8. For example, in the usbmon-100Hz-wifi.txt file, the transfer at timestamp 4033751111 has only 5 packets.) > > Maybe the analyzer trace will be more fruitful. Just because the > > driver got its data in time doesn't mean the data appeared on the wire. > > You said something about partial packets; what happened there? > Here is an audio recording and usb analyzer output. This is a 100hz > tone played while wifi traffic is being generated. I've confirmed that > errors captured in the analyzer trace correspond to errors in the > actual audio recording. I'd seen partial packets before but I don't > see them in this trace. I didn't look at the audio data because the errors show up already in the analyzer log. Every now and then there is a corrupted packet. Either there's too much contention for the memory bus or else there's some sort of electromagnetic interference. > > Also, can you post the portion of /sys/kernel/debug/usb/devices that > > describes the sound card? > Here's the host controller and sound card. > > T: Bus=01 Lev=00 Prnt=00 Port=00 Cnt=00 Dev#= 1 Spd=480 MxCh= 1 > B: Alloc= 0/800 us ( 0%), #Int= 0, #Iso= 0 > D: Ver= 2.00 Cls=09(hub ) Sub=00 Prot=01 MxPS=64 #Cfgs= 1 > P: Vendor=1d6b ProdID=0002 Rev= 3.03 > S: Manufacturer=Linux 3.3.8 ehci_hcd > S: Product=Generic Platform EHCI Controller > S: SerialNumber=ehci-platform > C:* #Ifs= 1 Cfg#= 1 Atr=e0 MxPwr= 0mA > I:* If#= 0 Alt= 0 #EPs= 1 Cls=09(hub ) Sub=00 Prot=00 Driver=hub > E: Ad=81(I) Atr=03(Int.) MxPS= 4 Ivl=256ms > > T: Bus=01 Lev=01 Prnt=01 Port=00 Cnt=01 Dev#= 3 Spd=12 MxCh= 0 > D: Ver= 1.10 Cls=00(>ifc ) Sub=00 Prot=00 MxPS= 8 #Cfgs= 1 > P: Vendor=0d8c ProdID=0139 Rev= 1.00 > S: Manufacturer=C-Media Electronics Inc. > S: Product=USB PnP Sound Device > C:* #Ifs= 4 Cfg#= 1 Atr=80 MxPwr=100mA > I:* If#= 0 Alt= 0 #EPs= 0 Cls=01(audio) Sub=01 Prot=00 Driver=snd-usb-audio > I:* If#= 1 Alt= 0 #EPs= 0 Cls=01(audio) Sub=02 Prot=00 Driver=snd-usb-audio > I: If#= 1 Alt= 1 #EPs= 1 Cls=01(audio) Sub=02 Prot=00 Driver=snd-usb-audio > E: Ad=01(O) Atr=09(Isoc) MxPS= 200 Ivl=1ms > I:* If#= 2 Alt= 0 #EPs= 0 Cls=01(audio) Sub=02 Prot=00 Driver=snd-usb-audio > I: If#= 2 Alt= 1 #EPs= 1 Cls=01(audio) Sub=02 Prot=00 Driver=snd-usb-audio > E: Ad=82(I) Atr=09(Isoc) MxPS= 100 Ivl=1ms > I:* If#= 3 Alt= 0 #EPs= 1 Cls=03(HID ) Sub=00 Prot=00 Driver=(none) > E: Ad=87(I) Atr=03(Int.) MxPS= 4 Ivl=2ms Okay, that's about what I figured. 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
