Hi Takashi,
I'm encountering a strange issue when working with our MAN301 device and
external clock sync. I am currently using our kernel-side AV/C code to
switch between clock sources[1].
When I switch to an external clock source, the user-space ALSA code is not
able to change the clock rate anymore. This means that I cannot switch to
the external clock rate that the DICE is currently locked onto.
Here is a practical example / steps to reproduce:
1. Set the clock source to internal and the clock rate to an arbitrary
value (e.g. 44100) from the user-space. The relevant sections of
/proc/asound/card0/firewire/dice will then look like this:
global:
owner: ffc0:000100000000
notification: 00000040
nick name: Weiss MAN301
clock select: internal 44100
enable: 0
status: locked 44100
ext status: 00010001
sample rate: 44100
version: 1.0.12.0
clock caps: 44100 48000 88200 96000 176400 192000 aes1 aes2 aes3 wc
internal
clock source names: AES/EBU (XLR)\S/PDIF (RCA)\S/PDIF
(TOS)\Unused\Unused\Unused\Unused\Word Clock
(BNC)\Unused\Unused\Unused\Unused\Internal\\
ext status:
clock source: internal
locked: 1
rate: 44100
2. Set the clock source to external (e.g. aes1) through AV/C command[1]
and connect a digital input with a different clock rate (e.g. 48000).
Now the two sections of will look like this. You can see that the
external source status is "locked".
global:
owner: ffc0:000100000000
notification: 00000010
nick name: Weiss MAN301
clock select: aes1 44100
enable: 0
status: unlocked 44100
ext status: 00010001
sample rate: 44100
version: 1.0.12.0
clock caps: 44100 48000 88200 96000 176400 192000 aes1 aes2 aes3 wc
internal
clock source names: AES/EBU (XLR)\S/PDIF (RCA)\S/PDIF
(TOS)\Unused\Unused\Unused\Unused\Word Clock
(BNC)\Unused\Unused\Unused\Unused\Internal\\
ext status:
clock source: aes1
locked: 1
rate: 48000
3. Try to set the clock rate to 48000 from user-space ALSA. This will
fail. Only 44100 can be used. Example:
$ aplay --disable-resample 48000_S32.wav
Playing WAVE '48000_S32.wav' : Signed 32 bit Little Endian, Rate 48000
Hz, Stereo
Warning: rate is not accurate (requested = 48000Hz, got = 44100Hz)
The current workaround is going back to the internal clock source, switch
the clock rate to the one reported in the "ext status" section, and then
go back to the external clock source. This however does not feel quite
right.
I will be very grateful for any suggestion from your side.
Thank you and kind regards,
Michele Perrone
[1]https://github.com/weiss-engineering/snd-dice/blob/5a95496c0666048bc5bc8c07b3e1d74f392dc9a4/dice-avc.c#L436
