Re: [Line6linux-devel] (no subject)

[Stefan H. <ste...@gm...>]

On Thu, May 2, 2013 at 7:51 PM, Andrej Kruták <de...@an...> wrote:
> On Thu, May 2, 2013 at 4:39 PM, Stefan Hajnoczi <ste...@gm...> wrote:
>>
>> On Wed, May 1, 2013 at 9:33 PM, Andrej Kruták <de...@an...> wrote:
>> > On Wed, May 1, 2013 at 7:30 PM, Stefan Hajnoczi <ste...@gm...>
>> > wrote:
>> >>
>> >> On Wed, May 1, 2013 at 11:11 AM, Andrej Kruták <de...@an...> wrote:
>> >> > As I said, I don't know much about MIDI, so it's hard to tell for me,
>> >> > if
>> >> > the
>> >> > messages in X3 (bean) resemble it at all. What's your plan if it's
>> >> > different, is the userspace (planned t be) flexible enough? How is
>> >> > the
>> >> > profile uploading/downloading handled with the XT?
>> >>
>> >> Userspace should support multiple devices in a data-driven way -
>> >> adding support for a new device should (mostly) mean populating a
>> >> table of MIDI messages.
>> >>
>> > So in case there's no real MIDI in the device, you expect it to be
>> > somehow
>> > emulated by the driver, right? But for example the volume is send from
>> > X3 as
>> > a float number, while in MIDI (after a short look) it seems to be just
>> > an
>> > unsigned char....
>>
>> No, MIDI is not emulated by the driver.  In some cases the driver
>> spies on MIDI traffic or generates MIDI messages internally, but it
>> doesn't process MIDI messages and convert them into Line6-specific I/O
>> operations.
>>
>> MIDI is extensible and you can send arbitrary data over it (may
>> involve a 7-bit encoding).  Line6 uses a custom MIDI mapping and
>> parameters can be floats, fixed-point, etc.
>>
>> Can you explain what you mean regarding volume sent as a float?  Do
>> you have a traffic capture?
>>
>
> This is how the frames look like, either incoming or outcoming.
>
> OUT: 1C 00 01 00 | 06 00 0A 40 01 03 00 | 15 00 00 00 00 00 00 03 00 01 00
> 00 00 05 00 10 3F CE 66 33 3F
> IN:  1C 00 01 00 | 06 00 0A 03 00 40 00 | 15 00 00 00 00 00 00 03 00 01 00
> 00 00 05 00 10 3F 70 BE 79 3F
>
> My guess is that the first 4 bytes is frame header (more frames can be
> combined into single packet, first byte is frame len - 4). The second part
> is the packet header (with type and source/destination flags of some kind,
> or so it seems - the 40/03 bytes there). I'm not sure if some part of the
> last thing could be a MIDI message - as I said, I don't know too much in
> this regard. Anyhow, the last 4 bytes is an IEEE 754 float (seems like it's
> in big endian). The 05 byte means the volume knob id.
>
> So... you said MIDI is extensible - do you think the last part of the above
> (or last two parts?) could be somehow directly used in the userspace?

The CE and BE bytes indicate this is not part of a MIDI message.  MIDI
data is 7-bit, the top bit must be clear.  Therefore this cannot be
MIDI.

>> >> Don't expect anything close to the Line6 Editor working yet.
>> >> Personally, I care about a solid PCM and MIDI driver, but I don't care
>> >> so much about a Line6 Editor.  If someone invests the time then I'm
>> >> sure it would be doable in a couple of months.
>> >>
>> >
>> > For me, it'd be enough to just dump all the settings, put (some of) them
>> > back through some sys file, for example (or ioctl). According to the USB
>> > comm, it seems it's easily doable. Editing would be nice, I saw there's
>> > some
>> > work around that done already - but as yuo say, someone has to have time
>> > for
>> > it... :)
>>
>> Dumping the device is easy on the HD300, maybe it's the same on yours.
>>
> Not sure. X3 doesn't support MIDI (no midi in/out ports on the device
> itself) according to the specs. But I doubt they have completely different
> HW for X3 and X3 Live (which has MIDI), so the protocol could be the same -
> and the USB data could be indeed some encoded MIDI messages...
>
>
>> The device has a MIDI dump option available in an options menu.  You
>> can select whether to dump just the current patch or all patches.
>>
>> When you activate MIDI dump the device sends all the patches over
>> MIDI.  On your computer you can use amidi(1) to save this to file.
>>
>> Later you use amidi(1) to send the sysex back to the device, restoring
>> the patch(es).
>>
>> If you don't enjoy using amidi(1) I bet some of the graphical DAWs or
>> MIDI tools under Linux also support storing/loading sysex dumps.
>>
> I'll try to read something about this (sysex, MIDI format etc.) so I don't
> bother you with basic stuff..

http://www.midi.org/techspecs/midimessages.php

For example, switching to patch 1 would be:
Program Change (channel=0, patch=0):
C0 00

By the way, the table shows why MIDI uses 7-bit data.  Status bytes
have the top bit set, data bytes have the top bit cleared.

> Anyhow, back to the audio stream. How does the data transfer work on HD300?
> Is there any setup, or you just read/write the appropriate USB ports?

HD300 audio is just PCM data sent to/received via isochronous
transfer.  No setup is required.

Some of the other devices have more elaborate setup procedures where
several messages are exchanged with the device.  But once set up, they
also just use iso USB transfers of PCM data.

Stefan