Re: [LAD] A question for USB/MIDI experts

On 08 Apr 2016, at 22:05, Fons Adriaensen <fons(a)linuxaudio.org> wrote: Hello all, Sadly I won't be able to make it to the miniLAC as work keeps me in München during the weekend :-( For those who'll be there, have a good time ! Meanwhile I'm trying to understand the following: I'm using a Novation LaunchControl (8 pads and 16 rotary controllers). When I use it via ALSA sequencer, I get the expected MIDI events: note on/off, controller, and sysex. When I access it directly as a USB device using libusb, I see the expected MIDI data, but with some extra bytes, e.g. (all values in hex): [09] 90 09 7f (note on) [08] 80 09 00 (note off) [0b] b0 15 23 (controller) [04] f0 00 20 [04] 29 02 0A [07] 77 00 ff (sysex) where the bytes in [] are the ones that are *not* part of the MIDI message. Now since things work perfectly with ALSA sequencer without required a specific driver, either * ALSA knowns about the details of this particular device, * or these extra bytes are part of some standard. Given that there seems to be one extra byte for every three expected ones, could it be that this is some format that encodes 24 bits in 32 ? lsusb output for this device is: Bus 003 Device 004: ID 1235:0034 Focusrite-Novation Device Descriptor: bLength 18 bDescriptorType 1 bcdUSB 1.10 bDeviceClass 0 bDeviceSubClass 0 bDeviceProtocol 0 bMaxPacketSize0 64 idVendor 0x1235 Focusrite-Novation idProduct 0x0034 bcdDevice 0.00 iManufacturer 1 Focusrite A.E. Ltd iProduct 2 Launch Control iSerial 0 bNumConfigurations 1 Configuration Descriptor: bLength 9 bDescriptorType 2 wTotalLength 82 bNumInterfaces 2 bConfigurationValue 1 iConfiguration 0 bmAttributes 0x80 (Bus Powered) MaxPower 60mA Interface Descriptor: bLength 9 bDescriptorType 4 bInterfaceNumber 0 bAlternateSetting 0 bNumEndpoints 0 bInterfaceClass 1 Audio bInterfaceSubClass 1 Control Device bInterfaceProtocol 0 iInterface 3 Launch Control AudioControl Interface Descriptor: bLength 9 bDescriptorType 36 bDescriptorSubtype 1 (HEADER) bcdADC 1.00 wTotalLength 9 bInCollection 1 baInterfaceNr( 0) 1 Interface Descriptor: bLength 9 bDescriptorType 4 bInterfaceNumber 1 bAlternateSetting 0 bNumEndpoints 2 bInterfaceClass 1 Audio bInterfaceSubClass 3 MIDI Streaming bInterfaceProtocol 0 iInterface 3 Launch Control MIDIStreaming Interface Descriptor: bLength 7 bDescriptorType 36 bDescriptorSubtype 1 (HEADER) bcdADC 1.00 wTotalLength 46 MIDIStreaming Interface Descriptor: bLength 6 bDescriptorType 36 bDescriptorSubtype 2 (MIDI_IN_JACK) bJackType 1 Embedded bJackID 1 iJack 0 MIDIStreaming Interface Descriptor: bLength 9 bDescriptorType 36 bDescriptorSubtype 3 (MIDI_OUT_JACK) bJackType 1 Embedded bJackID 2 bNrInputPins 1 baSourceID( 0) 1 BaSourcePin( 0) 1 iJack 0 Endpoint Descriptor: bLength 7 bDescriptorType 5 bEndpointAddress 0x81 EP 1 IN bmAttributes 3 Transfer Type Interrupt Synch Type None Usage Type Data wMaxPacketSize 0x0040 1x 64 bytes bInterval 1 MIDIStreaming Endpoint Descriptor: bLength 5 bDescriptorType 37 bDescriptorSubtype 1 (GENERAL) bNumEmbMIDIJack 1 baAssocJackID( 0) 2 Endpoint Descriptor: bLength 7 bDescriptorType 5 bEndpointAddress 0x02 EP 2 OUT bmAttributes 3 Transfer Type Interrupt Synch Type None Usage Type Data wMaxPacketSize 0x0040 1x 64 bytes bInterval 1 MIDIStreaming Endpoint Descriptor: bLength 5 bDescriptorType 37 bDescriptorSubtype 1 (GENERAL) bNumEmbMIDIJack 1 baAssocJackID( 0) 1 Any info much appreciated !! Ciao, -- FA A world of exhaustive, reliable metadata would be an utopia. It's also a pipe-dream, founded on self-delusion, nerd hubris and hysterically inflated market opportunities. (Cory Doctorow) _______________________________________________ Linux-audio-dev mailing list Linux-audio-dev(a)lists.linuxaudio.org http://lists.linuxaudio.org/listinfo/linux-audio-dev