> > My configuration: > ----------------- > > Host: Freescale i.MX512 with ARM Cortex A8 (USB 2.0 host controller) Linux > kernel: 2.6.31, using EHCI USB driver > Hub: 4-PORT USB 1.1 HUB (Texas Instruments PN: tusb2046b) > Devices: 4 USB 1.1 audio codecs (Texas Instruments PN: pcm2901) > > Note: each codec is being used in R/W access, so with 4 codecs, I have > 4 playback and 4 capture streams. > > My problem: > ----------- > > I have usb urb leaks when connecting more than 1 codec to the USB 1.1 Hub. > (the result is that some of the audio data is not transferred, part of the sound is > simply missing) No problem when using only 1 of the 4 codecs connected to the > hub; When I connect a second codec, the sound quality starts to degrade. With > 3 codecs, we just cannot recognize a speach. > > Tests and observations: > ----------------------- > > Since I have 3 usb ports available on the i.MX512, I tried to connect > 3 codecs directly on USB ports: the sound is perfect on each of the three ports. > > I bought a consumer USB 2.0 Hub: no problem when using 3 codecs connected > to that Hub, however, the audio will completly stop on all channels when > connecting the 4th codec. > > I checked the communication between the Hub (USB 1.1) and the Host > controller (USB 2.0) with a scope and concluded that the communication speed > is 1.5 MBytes/s has expected (so the communication is downgraded to USB 1.1, > since codecs and hub are USB > 1.1 devices). > > Also, I know that there is physically enough bandwidth to transfer the data for > two reasons: > 1) I have an older CPU with a USB 1.1 host controller (using the OHCI driver), > using the same hub and the same codecs: works like a champ, using less than > 50% of the available bandwidth (observed with a > scope) > 2) 1 audio stream is 32khz-mono, 16 bits = 64 kB/s, > 4 codecs = 8 streams(R/W) x 64 kB/s = 512 kB/s (out of 1.5MB/s) > > I noticed that my sound problem starts happening with only 2 codecs > (4 streams, 256 kB/s). I first thought that it was a bandwidth limitation, so I > decided to connect only 1 codec using more bandwidth. > I configured it to 48khz-stereo (16-bits), using 384 kB/s for both read and write > streams: no problem. With that configuration, the scope shows about 30% of > total bandwidth usage (300us used out of 1ms periods). Then, I added a second > codec (48khz-stereo-16bits): very strange, now the total bandwidth usage felt > down to about 200us, which seems to keep the same, whatever the number of > codec I add (I also tried 3 and 4...). So it looks like the scheduler is not able to > properly allocate Isochronous time slots when more than one device is > connected to the hub. However, without the hub, it works perfectly. > I am wonder if it is similar problem I met when using multiple interrupt transfers, when you find you lose the data, try to run 'top' to show cpu utilization, if it is close to 100%, it means the ehci can't queue request in time, so the host can't send IN token in time. Using a USB bus analyzer can also verify it. Peter > Another interresting fact is that at application level, the Read and Write > operations are returning the good amount of bytes read/written. > This is not the case at kernel level: I noticed that function "usb_submit_urb" > (from /drivers/usb/core/urb.c) will only tranfer part of the "urbs" when the > sound is degraded. I tried to figure out where the leak comes from without > success. Also, there are no error messages from kernel so everything appears > to work well, excepted that part of the sound is missing! > > I can't change my hardware (this is in the hand of customers), so the only > possible solution for me is to correct the software. > > I tried to change my ehci driver with the one from kernel 2.6.39.4 but did not > work, same problem. > > Question: > --------- > > Before attempting to upgrade to an earlier kernel driver (this is a fairly big > amount of work), I would really like to know if this problem would still be in the > 3.x kernels. Has anyone seen that issue in 3.x kernels? > > I am pretty new to USB driver debugging, so any ideas of where/how to find > solutions will be appreciated. Thank you very much in advance for the support. > Also don't hesitate to redirect me if I'm not at the right place to ask these > questions. I can also provide some code if someone need it to help. > > Attached is a dump of my "dmesg" after startup. > > Michael Tessier > > > > > > -- 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
