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