Re: [alsa-devel] Controlling the Tascam FW-1884

7 Oct 2018

      Hi Scott,
On Oct 2 2018 12:16, Takashi Sakamoto wrote:
...
I have an idea to invervene them:

For control events, in kernel land, driver module detects

changes of set of bitflags for physical controls, then queue
events to tell the change to userspace applications
(e.g. poll(2)). The queued events include information about
changed bitflags (e.g. a shape of u32 data). Userspace
applications execute read(2) then get the bitflags, then parse
it and emit userspace event by ports in ALSA sequencer
subsystem.
The driver and userspace application should pay enough
attention to share the queue. The driver can drop the oldest
queued events if the queue is full.

For level meter, in kernel land, driver module caches the

recent value. Userspace applications execute ioctl(2) with
unique command (You can see this kind of commands in
'include/uapi/sound/firwire.h').
I prepare two remote branch as 'topic/tascam-userspace-take2' for kernel
driver[1] and libhinawa[2].
The patches for kernel driver adds two features below to firewire-tascam 
module:
  - SNDRV_FIREWIRE_IOCTL_TASCAM_STATUS ioctl command
  - 'struct snd_firewire_event_tascam_ctl' event notification
The patches for libhinawa adds two features below for g-i modules:
  - hinawa_snd_tscm_get_status() method
  - 'control' GObject signal
For example[3]:
```
$ cat test.py
#!/usr/bin/env python3
from sys import exit
from time import sleep
import gi
gi.require_version('Hinawa', '2.0')
from gi.repository import Hinawa
unit = Hinawa.SndTscm()
unit.open('/dev/snd/hwC2D0')
unit.listen()
req = Hinawa.FwReq()
def handle_control(self, index, flags):
     print('{0:02d}: {1:08x}'.format(index, flags))
     # data = bytearray(4)
     # You can check the flags and bright LED with proper values
     # in the data array.
     # print(req.write(self, 0xffff00000404, data))
unit.connect('control', handle_control)
while (True):
   msgs = unit.get_status()
   for i in range(len(msgs) // 2):
       left = i
       right = i + len(msgs) // 2
       print('{0:02d}: {1:08x}, {2:02d}: {3:08x}'.format(left, 
msgs[left], right, msgs[right]))
   sleep(0.1)
```
When running any scripts with your local build of libhinawa,
it's useful to set LD_LIBRARY_PATH/GI_TYPELIB_PATH properly.
```
$ export 
LD_LIBRARY_PATH="/home/username/git/libhinawa/build/src:${LD_LIBRARY_PATH}"
$ export 
GI_TYPELIB_PATH="/home/username/git/libhinawa/build/src:${GI_TYPELIB_PATH}"
$ ./sample.py
...
```
When starting packet streaming and operating control surface, you can
see dump with index and bitflags additionally to status dump.
```
...
06: fffeffff
06: ffffffff
06: feffffff
...
```
As I told, kernel driver emits events corresponding to quadlet 05-15.
If there's insufficiency, please inform it to me. If all things look
well, I'll submit patches for next merge window but .
[1] 
https://github.com/takaswie/snd-firewire-improve/tree/topic/tascam-userspace...
[2] https://github.com/takaswie/libhinawa/tree/topic/tascam-userspace-take2
[3] https://gist.github.com/takaswie/669fd4254c7b9fd631762fc61ac931f5
Thanks
Takashi Sakamoto