On Wed, 13 Apr 2016, Simon Wood wrote: > Hi all, > I have been struggling for the past few days to get a Tascam US-122L (USB > sound-card/midi interface) working, despite reading numerous forum > postings I have only been able to get the midi portion working. > > I note that the USB descriptor seems to be corrupt. It declares 2 > interfaces, but then describes 3 separate with the same interface number > for the last 2... could it be that this is confusing the Linux USB stack? > > I have attached a copy of the descriptor and an annotated 'lsusb -vv'. > ... My experience of lsusb is that it can get confused and report errors when there in fact aren't any, especially with vendor specific classes which it really can only guess at. > > Configuration Descriptor: > -- > 00000010 _____ 09 02 48 00 02 01 00 80 f0 ______________ |....H...........| > -- > bLength 9 > bDescriptorType 2 > wTotalLength 72 > bNumInterfaces 2 <------- 2 interfaces > bConfigurationValue 1 > iConfiguration 0 > bmAttributes 0x80 > (Bus Powered) > MaxPower 480mA > > > Interface Descriptor: <------ that's 1 > -- > 00000010 _________________________________ 09 04 00 00 00 |....H...........| > 00000020 ff 00 00 00 ____________________________________ |................| > -- > bLength 9 > bDescriptorType 4 > bInterfaceNumber 0 > bAlternateSetting 0 > bNumEndpoints 0 > bInterfaceClass 255 Vendor Specific Class > bInterfaceSubClass 0 > bInterfaceProtocol 0 > iInterface 0 > > Interface Descriptor: <------ that's 2 > -- > 00000020 ___________ 09 04 01 00 00 ff 00 00 00 ________ |................| > -- > bLength 9 > bDescriptorType 4 > bInterfaceNumber 1 > bAlternateSetting 0 > bNumEndpoints 0 > bInterfaceClass 255 Vendor Specific Class > bInterfaceSubClass 0 > bInterfaceProtocol 0 > iInterface 0 > > Interface Descriptor: <------ that's 3, err wait... > -- > 00000020 _______________________________________ 09 04 01 |................| > 00000030 01 04 ff 00 00 00 ______________________________ |..........N.....| > -- > bLength 9 > bDescriptorType 4 > bInterfaceNumber 1 <------ interface duplicate!! > bAlternateSetting 1 > bNumEndpoints 4 My knowledge of USB is sketchy since I rarely work with it on this level (I was working on some quirks for the Zoom R16 a while ago), but I note that bAlternateSetting is 1, which I think means that the device offers two specific ways of implementing interface no. 1. Actually, IIRC, alternate setting 0 normally means an interface which essentially is disabled, and it would certainly seem so here as the two first interface descriptors have 0 endpoints, whereas the one here has 4. My wild guess is that this interface 1 / altsetting 1 represents the actual device in normal operation, as has 4 endpoints ... > bInterfaceClass 255 Vendor Specific Class > bInterfaceSubClass 0 > bInterfaceProtocol 0 > iInterface 0 > > Endpoint Descriptor: > ... > bLength 9 > bDescriptorType 5 > bEndpointAddress 0x81 EP 1 IN > bmAttributes 5 > Transfer Type Isochronous > Synch Type Asynchronous > Usage Type Data > wMaxPacketSize 0x004e 1x 78 bytes > ... > Endpoint Descriptor: > ... > bDescriptorType 5 > bEndpointAddress 0x02 EP 2 OUT > bmAttributes 5 > Transfer Type Isochronous > Synch Type Asynchronous > Usage Type Data > wMaxPacketSize 0x004e 1x 78 bytes > ... > Endpoint Descriptor: > ... > bDescriptorType 5 > bEndpointAddress 0x83 EP 3 IN > bmAttributes 2 > Transfer Type Bulk > Synch Type None > Usage Type Data > wMaxPacketSize 0x0009 1x 9 bytes > ... > Endpoint Descriptor: > ... > bDescriptorType 5 > bEndpointAddress 0x04 EP 4 OUT > bmAttributes 2 > Transfer Type Bulk > Synch Type None > Usage Type Data > wMaxPacketSize 0x0200 1x 512 bytes > bInterval 4 > bRefresh 0 > bSynchAddress 0 ... the two first of which are the audio interface (which uses isochronous data transfers), and the other two are MIDI (bulk). I think (but could be wrong so don't take my word for it) it's a bit unusual that both MIDI and audio are represented by a single interface, but it certainly seems to be the case here. /Ricard -- Ricard Wolf Wanderlöf ricardw(at)axis.com Axis Communications AB, Lund, Sweden www.axis.com Phone +46 46 272 2016 Fax +46 46 13 61 30 _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
