USB Audio broken in kernel 3.18.7+

[Halloran]

I run an RPi as an audio server: mpd 0.19.7 using ALSA to output to a Schiit Modi USB DAC, serving MP3's and FLAC files.

Recently, I ran apt-get update, apt-get upgrade, and my kernel went from 3.12.28+ to 3.18.7+, and this completely broke the audio output. Audio was being output more or less as white noise, not as slightly distorted, and this was the case with the aplay utility as well as with MPD. After a lot of troubleshooting with MPD, ALSA, etc., I used rpi-update to downgrade to the 3.12.28+ kernel, and all is working fine....

No idea it this is limited to USB audio, or if the problem might be deeper, but wanted to report it. Am happy to help with more system information, etc.

[popcornmix]

sudo rpi-update f74b92120e0d469fc5c2dc85b2b5718d877e1cbb
is the latest 3.12 and
sudo rpi-update cad071ac50ddf8a9f3c7a5d808cfa0daf5effb45
is the oldest 3.18 kernel.
Can you test those two and report which work?

[Halloran]

Looks like the latest 3.12 works, the oldest 3.18 does not:

Ran:

sudo rpi-update f74b92120e0d469fc5c2dc85b2b5718d877e1cbb

got:

pi@framboise ~ $ uname -a
Linux framboise 3.12.36+ #737 PREEMPT Wed Jan 14 19:40:07 GMT 2015 armv6l GNU/Linux

Audio works

Ran

sudo rpi-update cad071ac50ddf8a9f3c7a5d808cfa0daf5effb45

got:

pi@framboise ~ $ uname -a
Linux framboise 3.18.3+ #739 PREEMPT Tue Jan 20 17:45:32 GMT 2015 armv6l GNU/Linux

Audio broken

[popcornmix]

Are you able to test the USB on a different platform (e.g. x86) with 3.18 kernel?

The point where it broke was switching to a newer upstream kernel rather than a change to any Pi specific code. It may be this is a common problem for that sound card with newer kernel versions.

Could be worth searching for similar problems on other platforms, in case there are known patches or workarounds.

[Halloran]

Testing on x86 is not something that I can do anytime soon, though I'll try to figure out a way to do that.... I have looked through a lot of Audio sites, and it's hard to isolate the issues mentioned there, b/c getting USB audio working on Ubuntu seems to be pretty confusing in the first place....

But thanks for that feedback. I will try to do more digging, and see if I can make any progress.

In my case, the 3.12.x kernel is not really a problem, so I'll admit that my motivation here is pretty low.

Again, let me know if there are other things you'd like me to check, and if I can get an x86 machine running 3.18 I'll post results here.

[P33M]

For reference, can you post a lsusb -v for the card in question?

At this point I'm not convinced this is a Pi-specific issue, namely because recent updates should have absolutely no effect on Pi 1 USB performance.

[Halloran]

Cannot figure out which device it is, as the manufacturer is not showing up, but here are the 2 possibilities:

Bus 001 Device 004: ID 0d8c:1319 C-Media Electronics, Inc. 
Couldn't open device, some information will be missing
Device Descriptor:
  bLength                18
  bDescriptorType         1
  bcdUSB               2.00
  bDeviceClass            0 (Defined at Interface level)
  bDeviceSubClass         0 
  bDeviceProtocol         0 
  bMaxPacketSize0        64
  idVendor           0x0d8c C-Media Electronics, Inc.
  idProduct          0x1319 
  bcdDevice            1.05
  iManufacturer           1 
  iProduct                2 
  iSerial                 0 
  bNumConfigurations      1
  Configuration Descriptor:
    bLength                 9
    bDescriptorType         2
    wTotalLength          214
    bNumInterfaces          3
    bConfigurationValue     1
    iConfiguration          0 
    bmAttributes         0xc0
      Self Powered
    MaxPower              500mA
    Interface Descriptor:
      bLength                 9
      bDescriptorType         4
      bInterfaceNumber        0
      bAlternateSetting       0
      bNumEndpoints           0
      bInterfaceClass         1 Audio
      bInterfaceSubClass      1 Control Device
      bInterfaceProtocol      0 
      iInterface              2 
      AudioControl Interface Descriptor:
        bLength                 9
        bDescriptorType        36
        bDescriptorSubtype      1 (HEADER)
        bcdADC               1.00
        wTotalLength           40
        bInCollection           1
        baInterfaceNr( 0)       1
      AudioControl Interface Descriptor:
        bLength                12
        bDescriptorType        36
        bDescriptorSubtype      2 (INPUT_TERMINAL)
        bTerminalID             1
        wTerminalType      0x0101 USB Streaming
        bAssocTerminal          0
        bNrChannels             2
        wChannelConfig     0x0003
          Left Front (L)
          Right Front (R)
        iChannelNames           0 
        iTerminal               0 
      AudioControl Interface Descriptor:
        bLength                 9
        bDescriptorType        36
        bDescriptorSubtype      3 (OUTPUT_TERMINAL)
        bTerminalID             7
        wTerminalType      0x0301 Speaker
        bAssocTerminal          0
        bSourceID              13
        iTerminal               0 
      AudioControl Interface Descriptor:
        bLength                10
        bDescriptorType        36
        bDescriptorSubtype      6 (FEATURE_UNIT)
        bUnitID                13
        bSourceID               1
        bControlSize            1
        bmaControls( 0)      0x01
          Mute Control
        bmaControls( 1)      0x00
        bmaControls( 2)      0x00
        iFeature                0 
    Interface Descriptor:
      bLength                 9
      bDescriptorType         4
      bInterfaceNumber        1
      bAlternateSetting       0
      bNumEndpoints           0
      bInterfaceClass         1 Audio
      bInterfaceSubClass      2 Streaming
      bInterfaceProtocol      0 
      iInterface              4 
    Interface Descriptor:
      bLength                 9
      bDescriptorType         4
      bInterfaceNumber        1
      bAlternateSetting       1
      bNumEndpoints           2
      bInterfaceClass         1 Audio
      bInterfaceSubClass      2 Streaming
      bInterfaceProtocol      0 
      iInterface              0 
      AudioStreaming Interface Descriptor:
        bLength                 7
        bDescriptorType        36
        bDescriptorSubtype      1 (AS_GENERAL)
        bTerminalLink           1
        bDelay                  1 frames
        wFormatTag              1 PCM
      AudioStreaming Interface Descriptor:
        bLength                20
        bDescriptorType        36
        bDescriptorSubtype      2 (FORMAT_TYPE)
        bFormatType             1 (FORMAT_TYPE_I)
        bNrChannels             2
        bSubframeSize           2
        bBitResolution         16
        bSamFreqType            4 Discrete
        tSamFreq[ 0]        44100
        tSamFreq[ 1]        48000
        tSamFreq[ 2]        88200
        tSamFreq[ 3]        96000
      Endpoint Descriptor:
        bLength                 9
        bDescriptorType         5
        bEndpointAddress     0x05  EP 5 OUT
        bmAttributes            5
          Transfer Type            Isochronous
          Synch Type               Asynchronous
          Usage Type               Data
        wMaxPacketSize     0x0188  1x 392 bytes
        bInterval               4
        bRefresh                0
        bSynchAddress         133
        AudioControl Endpoint Descriptor:
          bLength                 7
          bDescriptorType        37
          bDescriptorSubtype      1 (EP_GENERAL)
          bmAttributes         0x01
            Sampling Frequency
          bLockDelayUnits         0 Undefined
          wLockDelay              0 Undefined
      Endpoint Descriptor:
        bLength                 9
        bDescriptorType         5
        bEndpointAddress     0x85  EP 5 IN
        bmAttributes            1
          Transfer Type            Isochronous
          Synch Type               None
          Usage Type               Data
        wMaxPacketSize     0x0003  1x 3 bytes
        bInterval               4
        bRefresh                5
        bSynchAddress           0
    Interface Descriptor:
      bLength                 9
      bDescriptorType         4
      bInterfaceNumber        1
      bAlternateSetting       2
      bNumEndpoints           2
      bInterfaceClass         1 Audio
      bInterfaceSubClass      2 Streaming
      bInterfaceProtocol      0 
      iInterface              0 
      AudioStreaming Interface Descriptor:
        bLength                 7
        bDescriptorType        36
        bDescriptorSubtype      1 (AS_GENERAL)
        bTerminalLink           1
        bDelay                  1 frames
        wFormatTag              1 PCM
      AudioStreaming Interface Descriptor:
        bLength                20
        bDescriptorType        36
        bDescriptorSubtype      2 (FORMAT_TYPE)
        bFormatType             1 (FORMAT_TYPE_I)
        bNrChannels             2
        bSubframeSize           3
        bBitResolution         24
        bSamFreqType            4 Discrete
        tSamFreq[ 0]        44100
        tSamFreq[ 1]        48000
        tSamFreq[ 2]        88200
        tSamFreq[ 3]        96000
      Endpoint Descriptor:
        bLength                 9
        bDescriptorType         5
        bEndpointAddress     0x05  EP 5 OUT
        bmAttributes            5
          Transfer Type            Isochronous
          Synch Type               Asynchronous
          Usage Type               Data
        wMaxPacketSize     0x024c  1x 588 bytes
        bInterval               4
        bRefresh                0
        bSynchAddress         133
        AudioControl Endpoint Descriptor:
          bLength                 7
          bDescriptorType        37
          bDescriptorSubtype      1 (EP_GENERAL)
          bmAttributes         0x01
            Sampling Frequency
          bLockDelayUnits         0 Undefined
          wLockDelay              0 Undefined
      Endpoint Descriptor:
        bLength                 9
        bDescriptorType         5
        bEndpointAddress     0x85  EP 5 IN
        bmAttributes            1
          Transfer Type            Isochronous
          Synch Type               None
          Usage Type               Data
        wMaxPacketSize     0x0003  1x 3 bytes
        bInterval               4
        bRefresh                5
        bSynchAddress           0
    Interface Descriptor:
      bLength                 9
      bDescriptorType         4
      bInterfaceNumber        2
      bAlternateSetting       0
      bNumEndpoints           1
      bInterfaceClass         3 Human Interface Device
      bInterfaceSubClass      0 No Subclass
      bInterfaceProtocol      0 None
      iInterface              0 
        HID Device Descriptor:
          bLength                 9
          bDescriptorType        33
          bcdHID               1.00
          bCountryCode            0 Not supported
          bNumDescriptors         1
          bDescriptorType        34 Report
          wDescriptorLength      24
         Report Descriptors: 
           ** UNAVAILABLE **
      Endpoint Descriptor:
        bLength                 7
        bDescriptorType         5
        bEndpointAddress     0x84  EP 4 IN
        bmAttributes            3
          Transfer Type            Interrupt
          Synch Type               None
          Usage Type               Data
        wMaxPacketSize     0x0010  1x 16 bytes
        bInterval               4

[pssc]

USB audio working
Bus 001 Device 004: ID 08bb:2902 Texas Instruments Japan PCM2902 Audio Codec

Hardware : BCM2708
Revision : 000f

Linux raspberrypi 3.18.9

[P33M]

@Halloran With audio playing (either MPD or aplay) can you post the output of cat /proc/asound/card1/stream0 - and compare the 3.12 version with 3.18 to see if it's any different?

[P33M]

@Halloran I've just noticed that the device is likely to use a High-Speed chipset (CM6631A). Can you post a lsusb -t to confirm?

[sanjibm]

I can second this USB audio issue. I had to downgrade my kernel to 3.12 to get USB audio to work. BTW, I am also using a Schiit Modi USB DAC. Anything beyond 3.12 breaks the audio into crackles and corruption/noise.

This might have a connection with the nrpacks option in the snd-usb-audio module. I noticed that this option is no longer supported in the latest kernels. According to modinfo, this sets the: Max. number of packets per URB. (int). Setting this to "nrpacks=1" should allow latencies in the area of 4-6 msecs.

So if it shows up in the kernel as a valid parameter, then all is well:

modinfo snd-usb-audio | grep ^parm:

If nrpacks isn't available, then USB audio doesn't seem to work with the Schiit Modi DAC; this option has been recommended for other popular USB DACs too.

I am not sure, but it appears that the nrpacks option was removed as the configuration for setting the number of packets per URB has been made automatic, hence this is no longer needed. Clearly something seems to be going wrong with this new implementation, or perhaps I am missing a replacement bit of configuration for the new kernels. Need to investigate a bit more

[pssc]

"Anything beyond 3.12 breaks the audio into crackles and corruption/noise."

This would seem to be related to buffer settings in the audio subsystem have you tried upping buffer time and period count / buffer size for reliable usb audio try periodCount=5 bufferTime=113378,
I had to significantly up these for USB audio (internal pc=3 bt=50).

[P33M]

@pssc @sanjibm It it unlikely that these module parameters need altering from defaults. With 3.18 in the wild and packaged for the latest release of Raspbian, if these changes caused failures across all usb-audio devices then the entire world would be screaming on the forums. As of 3.18 (actually as of 3.13) the nrpacks parameter is redundant because the driver has a notionally saner algorithm for calculating the number of URBs required.

Both the reported problems are with a specific type of DAC. This DAC is unusual in being a high-speed device. There are differences with handling of packet intervals for high-speed Isochronous devices, which a move to 3.18 may have caused to change.

[pssc]

ok well event with my low speed devices I had to alter the application settings (not kernel) to get sane usb audio, if the system was under any load. I could also distort the USB audio by altering the spi bus frequency for the piftft screen (but I think that’s a different issue)
The above settings where tuned to cause ~3-4k buffer update for a given period, reducing the strain on the system, before this the some of the USB audio device I tried sounded like the world had ended. Other USB sound devices where tolerant of lower settings(but caused horribly distorted audio on others). but still significantly more than the defaults alsa settings for internal output, which I guess reflects the latencies in the USB system and the occasion URB drop.

[Halloran]

@P33M I've had to travel so do not have access to the machine at the moment. Will get you the info you requested above, but it might be a couple of days.

[pssc]

Looking at one of my home PI's the least tolerant device I have was a
Bus 001 Device 005: ID 0d8c:0103 C-Media Electronics, Inc. CM102-A+/102S+ Audio Controller
which looks like it may me similar to the chip set in the above mentioned DAC.
With this device I also found a reboot didn’t recover from the distorting and it need a complete power removal from the pi to restore reasonable audio.