Hi Laurent,

   here the results of my tests:

MaxPayloadTransferSize Value Returned from device Result 0 128 uvcvideo: USB isochronous frame lost (-71). 1 128 uvcvideo: USB isochronous frame lost (-71). 42 128 uvcvideo: USB isochronous frame lost (-71). 1024 1024 works right with few USB iso frame lost 0xFFFF 3072 no error but also no capture :-(

My conclusion is that MaxPayloadTransferSize, regardless of specification, is not readonly... seems to be that device round this value to the closest that is supported (see also my lsusb in file lsusb.txt).

I think that the right bandwidth allocation must be calculated in the driver and set up in the device (the same you have done for frameinterval value :-).

BR Simone.

Laurent Pinchart wrote:
Hi Simone,

On Tuesday 03 February 2009, Simone Freddio wrote:
Hi Jan, hi Laurent...

    i have the same problem with different webcam... i think to have
found the problem, Laurent tell me if i am wrong, i'll go to explain:

    The problem is in the bandwidth, the uvcdriver ALWAYS ask to usb
layer a dw_MaxPayloadTransferSize that is fetched only when the device
is opening;

    In my case is always set to 3072 (3x1024). I have tried changing
uvc_video.c in a very dirty manner (excuse me Laurent)

Don't worry :-)

in this way:
    In function 'uvc_set_video_ctrl' where there is:
     put_unaligned_le32(ctrl->dwMaxVideoFrameSize, &data[18]);
     put_unaligned_le32(ctrl->dwMaxPayloadTransferSize, &data[22]);

    i have commented out the second line and changed it in:
    put_unaligned_le32(1024, &data[22]);

    In this way i have always force uvc driver to ask for a payload size
of 1024.

According to the UVC 1.1 specification, the dwMaxPayloadTransferSize is set by the device and read only from the host. The value set by the host shouldn't matter.

    After recompiling, reinstalling, unload e load the module, i can get
two webcam working fine and simultaneously.

    Now i didn't have a big experience and i can't change source myself
in the right way... but i think that my observation can be usefull.

It is, thanks.

    I think that the best way to re-negotiate the bandwidth is to set
video streaming parameters (framesize and frameinterval) and after ask
the device wich bandwidth it requests.

That's exactly what the driver does. In uvc_probe_video, each SET_CUR request is followed by a GET_CUR to retrieve the bandwidth requested by the camera.

    In a short way, at the end of uvc_set_video_ctrl function a call to
uvc_get_video_ctrl will solve the problem... what do you think Laurent?)

This is already handled by uvc_probe_video. From your report it seems that the device doesn't touch the dwMaxPayloadTransferSize at all and just returns the value sets by the host.

Could you (or Jan) try to set dwMaxPayloadTransferSize to a weird value (let's say 42) and see what the device returns in the next GET_CUR call ?

Best regards,

Laurent Pinchart


Bus 001 Device 005: ID 0ac8:332d Z-Star Microelectronics Corp. 
Device Descriptor:
  bLength                18
  bDescriptorType         1
  bcdUSB               2.00
  bDeviceClass          239 Miscellaneous Device
  bDeviceSubClass         2 ?
  bDeviceProtocol         1 Interface Association
  bMaxPacketSize0        64
  idVendor           0x0ac8 Z-Star Microelectronics Corp.
  idProduct          0x332d 
  bcdDevice            1.00
  iManufacturer           1 Vimicro Corp.
  iProduct                2 Vega USB 2.0 Camera.
  iSerial                 0 
  bNumConfigurations      1
  Configuration Descriptor:
    bLength                 9
    bDescriptorType         2
    wTotalLength          581
    bNumInterfaces          2
    bConfigurationValue     1
    iConfiguration          0 
    bmAttributes         0x80
      (Bus Powered)
    MaxPower              500mA
    Interface Association:
      bLength                 8
      bDescriptorType        11
      bFirstInterface         0
      bInterfaceCount         2
      bFunctionClass         14 Video
      bFunctionSubClass       3 Video Interface Collection
      bFunctionProtocol       0 
      iFunction               2 Vega USB 2.0 Camera.
    Interface Descriptor:
      bLength                 9
      bDescriptorType         4
      bInterfaceNumber        0
      bAlternateSetting       0
      bNumEndpoints           1
      bInterfaceClass        14 Video
      bInterfaceSubClass      1 Video Control
      bInterfaceProtocol      0 
      iInterface              2 Vega USB 2.0 Camera.
      VideoControl Interface Descriptor:
        bLength                13
        bDescriptorType        36
        bDescriptorSubtype      1 (HEADER)
        bcdUVC               1.00
        wTotalLength           79
        dwClockFrequency       24.000000MHz
        bInCollection           1
        baInterfaceNr( 0)       1
      VideoControl Interface Descriptor:
        bLength                18
        bDescriptorType        36
        bDescriptorSubtype      2 (INPUT_TERMINAL)
        bTerminalID             1
        wTerminalType      0x0201 Camera Sensor
        bAssocTerminal          0
        iTerminal               0 
        wObjectiveFocalLengthMin      0
        wObjectiveFocalLengthMax      0
        wOcularFocalLength            0
        bControlSize                  3
        bmControls           0x0004000a
          Auto-Exposure Mode
          Exposure Time (Absolute)
          Privacy
      VideoControl Interface Descriptor:
        bLength                11
        bDescriptorType        36
        bDescriptorSubtype      5 (PROCESSING_UNIT)
      Warning: Descriptor too short
        bUnitID                 2
        bSourceID               1
        wMaxMultiplier          0
        bControlSize            2
        bmControls     0x0000177f
          Brightness
          Contrast
          Hue
          Saturation
          Sharpness
          Gamma
          White Balance Temperature
          Backlight Compensation
          Gain
          Power Line Frequency
          White Balance Temperature, Auto
        iProcessing             0 
        bmVideoStandards     0x 9
          None
          SECAM - 625/50
      VideoControl Interface Descriptor:
        bLength                 9
        bDescriptorType        36
        bDescriptorSubtype      3 (OUTPUT_TERMINAL)
        bTerminalID             3
        wTerminalType      0x0101 USB Streaming
        bAssocTerminal          0
        bSourceID               2
        iTerminal               0 
      VideoControl Interface Descriptor:
        bLength                28
        bDescriptorType        36
        bDescriptorSubtype      6 (EXTENSION_UNIT)
        bUnitID                 4
        guidExtensionCode         {5dc717a9-1941-da11-ae0e-000d56ac7b4c}
        bNumControl            13
        bNrPins                 1
        baSourceID( 0)          1
        bControlSize            3
        bmControls( 0)       0xf9
        bmControls( 1)       0x1f
        bmControls( 2)       0x18
        iExtension              0 
      Endpoint Descriptor:
        bLength                 7
        bDescriptorType         5
        bEndpointAddress     0x81  EP 1 IN
        bmAttributes            3
          Transfer Type            Interrupt
          Synch Type               None
          Usage Type               Data
        wMaxPacketSize     0x000a  1x 10 bytes
        bInterval               5
    Interface Descriptor:
      bLength                 9
      bDescriptorType         4
      bInterfaceNumber        1
      bAlternateSetting       0
      bNumEndpoints           0
      bInterfaceClass        14 Video
      bInterfaceSubClass      2 Video Streaming
      bInterfaceProtocol      0 
      iInterface              0 
      VideoStreaming Interface Descriptor:
        bLength                            14
        bDescriptorType                    36
        bDescriptorSubtype                  1 (INPUT_HEADER)
        bNumFormats                        1
        wTotalLength                      343
        bEndPointAddress                  130
        bmInfo                              0
        bTerminalLink                       3
        bStillCaptureMethod                 2
        bTriggerSupport                     1
        bTriggerUsage                       1
        bControlSize                        1
        bmaControls( 0)                    27
      VideoStreaming Interface Descriptor:
        bLength                            27
        bDescriptorType                    36
        bDescriptorSubtype                  4 (FORMAT_UNCOMPRESSED)
        bFormatIndex                        1
        bNumFrameDescriptors                5
        guidFormat                            
{59555932-0000-1000-8000-00aa00389b71}
        bBitsPerPixel                      16
        bDefaultFrameIndex                  1
        bAspectRatioX                       0
        bAspectRatioY                       0
        bmInterlaceFlags                 0x00
          Interlaced stream or variable: No
          Fields per frame: 1 fields
          Field 1 first: No
          Field pattern: Field 1 only
          bCopyProtect                      0
      VideoStreaming Interface Descriptor:
        bLength                            54
        bDescriptorType                    36
        bDescriptorSubtype                  5 (FRAME_UNCOMPRESSED)
        bFrameIndex                         1
        bmCapabilities                   0x00
          Still image unsupported
        wWidth                            640
        wHeight                           480
        dwMinBitRate                 24576000
        dwMaxBitRate                147456000
        dwMaxVideoFrameBufferSize      614400
        dwDefaultFrameInterval         333333
        bFrameIntervalType                  7
        dwFrameInterval( 0)            333333
        dwFrameInterval( 1)            400000
        dwFrameInterval( 2)            500000
        dwFrameInterval( 3)            666667
        dwFrameInterval( 4)           1000000
        dwFrameInterval( 5)           1333333
        dwFrameInterval( 6)           2000000
      VideoStreaming Interface Descriptor:
        bLength                            54
        bDescriptorType                    36
        bDescriptorSubtype                  5 (FRAME_UNCOMPRESSED)
        bFrameIndex                         2
        bmCapabilities                   0x00
          Still image unsupported
        wWidth                            352
        wHeight                           288
        dwMinBitRate                 24576000
        dwMaxBitRate                147456000
        dwMaxVideoFrameBufferSize      202752
        dwDefaultFrameInterval         333333
        bFrameIntervalType                  7
        dwFrameInterval( 0)            333333
        dwFrameInterval( 1)            400000
        dwFrameInterval( 2)            500000
        dwFrameInterval( 3)            666667
        dwFrameInterval( 4)           1000000
        dwFrameInterval( 5)           1333333
        dwFrameInterval( 6)           2000000
      VideoStreaming Interface Descriptor:
        bLength                            54
        bDescriptorType                    36
        bDescriptorSubtype                  5 (FRAME_UNCOMPRESSED)
        bFrameIndex                         3
        bmCapabilities                   0x00
          Still image unsupported
        wWidth                            320
        wHeight                           240
        dwMinBitRate                 24576000
        dwMaxBitRate                147456000
        dwMaxVideoFrameBufferSize      153600
        dwDefaultFrameInterval         333333
        bFrameIntervalType                  7
        dwFrameInterval( 0)            333333
        dwFrameInterval( 1)            400000
        dwFrameInterval( 2)            500000
        dwFrameInterval( 3)            666667
        dwFrameInterval( 4)           1000000
        dwFrameInterval( 5)           1333333
        dwFrameInterval( 6)           2000000
      VideoStreaming Interface Descriptor:
        bLength                            54
        bDescriptorType                    36
        bDescriptorSubtype                  5 (FRAME_UNCOMPRESSED)
        bFrameIndex                         4
        bmCapabilities                   0x00
          Still image unsupported
        wWidth                            176
        wHeight                           144
        dwMinBitRate                 24576000
        dwMaxBitRate                147456000
        dwMaxVideoFrameBufferSize       50688
        dwDefaultFrameInterval         333333
        bFrameIntervalType                  7
        dwFrameInterval( 0)            333333
        dwFrameInterval( 1)            400000
        dwFrameInterval( 2)            500000
        dwFrameInterval( 3)            666667
        dwFrameInterval( 4)           1000000
        dwFrameInterval( 5)           1333333
        dwFrameInterval( 6)           2000000
      VideoStreaming Interface Descriptor:
        bLength                            54
        bDescriptorType                    36
        bDescriptorSubtype                  5 (FRAME_UNCOMPRESSED)
        bFrameIndex                         5
        bmCapabilities                   0x00
          Still image unsupported
        wWidth                            160
        wHeight                           120
        dwMinBitRate                 24576000
        dwMaxBitRate                147456000
        dwMaxVideoFrameBufferSize       38400
        dwDefaultFrameInterval         333333
        bFrameIntervalType                  7
        dwFrameInterval( 0)            333333
        dwFrameInterval( 1)            400000
        dwFrameInterval( 2)            500000
        dwFrameInterval( 3)            666667
        dwFrameInterval( 4)           1000000
        dwFrameInterval( 5)           1333333
        dwFrameInterval( 6)           2000000
      VideoStreaming Interface Descriptor:
        bLength                            26
        bDescriptorType                    36
        bDescriptorSubtype                  3 (STILL_IMAGE_FRAME)
        bEndpointAddress                    0
        bNumImageSizePatterns               5
        wWidth( 0)                        640
        wHeight( 0)                       480
        wWidth( 1)                        352
        wHeight( 1)                       288
        wWidth( 2)                        320
        wHeight( 2)                       240
        wWidth( 3)                        176
        wHeight( 3)                       144
        wWidth( 4)                        160
        wHeight( 4)                       120
        bNumCompressionPatterns             5
      VideoStreaming Interface Descriptor:
        bLength                             6
        bDescriptorType                    36
        bDescriptorSubtype                 13 (COLORFORMAT)
        bColorPrimaries                     0 (Unspecified)
        bTransferCharacteristics            0 (Unspecified)
        bMatrixCoefficients                 0 (Unspecified)
    Interface Descriptor:
      bLength                 9
      bDescriptorType         4
      bInterfaceNumber        1
      bAlternateSetting       1
      bNumEndpoints           1
      bInterfaceClass        14 Video
      bInterfaceSubClass      2 Video Streaming
      bInterfaceProtocol      0 
      iInterface              0 
      Endpoint Descriptor:
        bLength                 7
        bDescriptorType         5
        bEndpointAddress     0x82  EP 2 IN
        bmAttributes            5
          Transfer Type            Isochronous
          Synch Type               Asynchronous
          Usage Type               Data
        wMaxPacketSize     0x0080  1x 128 bytes
        bInterval               1
    Interface Descriptor:
      bLength                 9
      bDescriptorType         4
      bInterfaceNumber        1
      bAlternateSetting       2
      bNumEndpoints           1
      bInterfaceClass        14 Video
      bInterfaceSubClass      2 Video Streaming
      bInterfaceProtocol      0 
      iInterface              0 
      Endpoint Descriptor:
        bLength                 7
        bDescriptorType         5
        bEndpointAddress     0x82  EP 2 IN
        bmAttributes            5
          Transfer Type            Isochronous
          Synch Type               Asynchronous
          Usage Type               Data
        wMaxPacketSize     0x0200  1x 512 bytes
        bInterval               1
    Interface Descriptor:
      bLength                 9
      bDescriptorType         4
      bInterfaceNumber        1
      bAlternateSetting       3
      bNumEndpoints           1
      bInterfaceClass        14 Video
      bInterfaceSubClass      2 Video Streaming
      bInterfaceProtocol      0 
      iInterface              0 
      Endpoint Descriptor:
        bLength                 7
        bDescriptorType         5
        bEndpointAddress     0x82  EP 2 IN
        bmAttributes            5
          Transfer Type            Isochronous
          Synch Type               Asynchronous
          Usage Type               Data
        wMaxPacketSize     0x0400  1x 1024 bytes
        bInterval               1
    Interface Descriptor:
      bLength                 9
      bDescriptorType         4
      bInterfaceNumber        1
      bAlternateSetting       4
      bNumEndpoints           1
      bInterfaceClass        14 Video
      bInterfaceSubClass      2 Video Streaming
      bInterfaceProtocol      0 
      iInterface              0 
      Endpoint Descriptor:
        bLength                 7
        bDescriptorType         5
        bEndpointAddress     0x82  EP 2 IN
        bmAttributes            5
          Transfer Type            Isochronous
          Synch Type               Asynchronous
          Usage Type               Data
        wMaxPacketSize     0x0b00  2x 768 bytes
        bInterval               1
    Interface Descriptor:
      bLength                 9
      bDescriptorType         4
      bInterfaceNumber        1
      bAlternateSetting       5
      bNumEndpoints           1
      bInterfaceClass        14 Video
      bInterfaceSubClass      2 Video Streaming
      bInterfaceProtocol      0 
      iInterface              0 
      Endpoint Descriptor:
        bLength                 7
        bDescriptorType         5
        bEndpointAddress     0x82  EP 2 IN
        bmAttributes            5
          Transfer Type            Isochronous
          Synch Type               Asynchronous
          Usage Type               Data
        wMaxPacketSize     0x0c00  2x 1024 bytes
        bInterval               1
    Interface Descriptor:
      bLength                 9
      bDescriptorType         4
      bInterfaceNumber        1
      bAlternateSetting       6
      bNumEndpoints           1
      bInterfaceClass        14 Video
      bInterfaceSubClass      2 Video Streaming
      bInterfaceProtocol      0 
      iInterface              0 
      Endpoint Descriptor:
        bLength                 7
        bDescriptorType         5
        bEndpointAddress     0x82  EP 2 IN
        bmAttributes            5
          Transfer Type            Isochronous
          Synch Type               Asynchronous
          Usage Type               Data
        wMaxPacketSize     0x1380  3x 896 bytes
        bInterval               1
    Interface Descriptor:
      bLength                 9
      bDescriptorType         4
      bInterfaceNumber        1
      bAlternateSetting       7
      bNumEndpoints           1
      bInterfaceClass        14 Video
      bInterfaceSubClass      2 Video Streaming
      bInterfaceProtocol      0 
      iInterface              0 
      Endpoint Descriptor:
        bLength                 7
        bDescriptorType         5
        bEndpointAddress     0x82  EP 2 IN
        bmAttributes            5
          Transfer Type            Isochronous
          Synch Type               Asynchronous
          Usage Type               Data
        wMaxPacketSize     0x1400  3x 1024 bytes
        bInterval               1
Device Qualifier (for other device speed):
  bLength                10
  bDescriptorType         6
  bcdUSB               2.00
  bDeviceClass          239 Miscellaneous Device
  bDeviceSubClass         2 ?
  bDeviceProtocol         1 Interface Association
  bMaxPacketSize0        64
  bNumConfigurations      1
Device Status:     0x0000
  (Bus Powered)

Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Device Descriptor:
  bLength                18
  bDescriptorType         1
  bcdUSB               2.00
  bDeviceClass            9 Hub
  bDeviceSubClass         0 Unused
  bDeviceProtocol         0 Full speed (or root) hub
  bMaxPacketSize0        64
  idVendor           0x1d6b Linux Foundation
  idProduct          0x0002 2.0 root hub
  bcdDevice            2.06
  iManufacturer           3 Linux 2.6.27-9-generic ehci_hcd
  iProduct                2 EHCI Host Controller
  iSerial                 1 0000:00:1d.7
  bNumConfigurations      1
  Configuration Descriptor:
    bLength                 9
    bDescriptorType         2
    wTotalLength           25
    bNumInterfaces          1
    bConfigurationValue     1
    iConfiguration          0 
    bmAttributes         0xe0
      Self Powered
      Remote Wakeup
    MaxPower                0mA
    Interface Descriptor:
      bLength                 9
      bDescriptorType         4
      bInterfaceNumber        0
      bAlternateSetting       0
      bNumEndpoints           1
      bInterfaceClass         9 Hub
      bInterfaceSubClass      0 Unused
      bInterfaceProtocol      0 Full speed (or root) hub
      iInterface              0 
      Endpoint Descriptor:
        bLength                 7
        bDescriptorType         5
        bEndpointAddress     0x81  EP 1 IN
        bmAttributes            3
          Transfer Type            Interrupt
          Synch Type               None
          Usage Type               Data
        wMaxPacketSize     0x0004  1x 4 bytes
        bInterval              12
Hub Descriptor:
  bLength              11
  bDescriptorType      41
  nNbrPorts             8
  wHubCharacteristic 0x000a
    No power switching (usb 1.0)
    Per-port overcurrent protection
  bPwrOn2PwrGood       10 * 2 milli seconds
  bHubContrCurrent      0 milli Ampere
  DeviceRemovable    0x00 0x00
  PortPwrCtrlMask    0xff 0xff
 Hub Port Status:
   Port 1: 0000.0503 highspeed power enable connect
   Port 2: 0000.0503 highspeed power enable connect
   Port 3: 0000.0100 power
   Port 4: 0000.0100 power
   Port 5: 0000.0100 power
   Port 6: 0000.0100 power
   Port 7: 0000.0100 power
   Port 8: 0000.0100 power
Device Status:     0x0003
  Self Powered
  Remote Wakeup Enabled
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