[alsa-devel] Boss GT-001

[Ricard Wanderlof]

On Thu, 8 Oct 2015, Keith A. Milner wrote:

> On Thursday 08 Oct 2015 01:51:20 Keith A. Milner wrote:
> > On Tuesday 06 Oct 2015 20:58:01 Keith A. Milner wrote:
> > > OK, so it seems that this hardware is substantially the same as the GT-100
> > > which has previously (and recently) been raised as a problem on ALSA.
> > 
> > I'm getting somewhere...
> > 
> > With the following quirk I am getting audio playback with aplay. I have what
> > seems like correct MIDI interfaces working (although not fully tested).
> > 
> > However, recording does not seem to work.
> 
> I should add that, by "does not seem to work", the interface is seen, but 
> nothing records. When using audacity, for instance, the playhead seems to get 
> stuck and doesn't advance.

How does it look in Wireshark? Does the isochronous transfer for the 
capture direction start?

Actually, looking at your lsusb -v dump of the GT-001, I notice the 
following:

     Endpoint Descriptor:
        bLength                 7
        bDescriptorType         5
        bEndpointAddress     0x0d  EP 13 OUT
        bmAttributes            5
          Transfer Type            Isochronous
          Synch Type               Asynchronous
          Usage Type               Data
        wMaxPacketSize     0x0070  1x 112 bytes
        bInterval               1

      Endpoint Descriptor:
        bLength                 7
        bDescriptorType         5
        bEndpointAddress     0x8e  EP 14 IN
        bmAttributes           37
          Transfer Type            Isochronous
          Synch Type               Asynchronous
          Usage Type               Implicit feedback Data
        wMaxPacketSize     0x0070  1x 112 bytes
        bInterval               1

When the Isochronous Synch Type is Asynchronous, there must be a feedback 
channel where the USB device reports back information so that it can 
adjust the output sampling rate 
(http://wiki.osdev.org/Universal_Serial_Bus#Asynchronous_Endpoints).

I might be barking up the wrong tree here as I'm new to this, but it looks 
as if endpoint 0x8e is providing the feedback data, and there doesn't seem 
to be any other isochronous endpoint defined in the lsusb dump which could 
be used for the actual capture cdata.

I'm not sure what 'Implicit feedback Data' means exactly though - is the 
feedback data multiplexed with the capture data perhaps?

/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