>> right. you can choose word clock, but if there's no word clock source,
>> it will default back to the internal word clock source (the h/w does
>> this, not the driver).
>>
>Does the driver get notified of this?
no, its implicit in the operation "set clock source to word clock". if
you do that with no word clock signal present, you've just done the
same as "set clock source to internal". so arguably, the driver should
check for a word clock source first, but this limits application
choices in an unacceptable way. perhaps i *want* to change to word
clock now, then connect the cable ...
>> >If I arecord card0 at 96000, card1 still shows 48000 for its sample
>> >rate.
>>
>> thats correct. there is no 96kHz rate for ADAT. there is no way for
>> card1 to know that card0 is operating at "double speed mode". this has
>> always been a hack on all ADAT equipment: you have to explicitly tell
>> (by pressing a button or running some s/w) each end of the connection
>> that you're running in double speed, since at the low level, things
>> have stayed exactly the same: the bits still move at 48kHz. they just
>> send 1 "channel"'s worth over 2 channels.
>>
>even if using word clock? RME suggests word clock can go as low as 25khz
>to 105khz
absolutely not. word clock does NOT specify sample rate. its a clock
source, not a sample rate control. it can tick at any speed you like
while the sample rate changes independently. now, some devices will
use word clock in more constrained ways, so that slowing down the WC
signal will change the sample rate, but thats not inherent in the
technology.
the ADAT data stream has its own clock data present (in theory, its
self clocking; in practice, its unreliable) and an implicit sample
rate. if you connect two ADAT devices that have been configured to use
different rates, they will do more or less what you expect.
>> I can then not bring the cards back to 48000 or 44100 unless I
>> >unload and reload the modules--I get device or resource busy if I try to
>> >switch back.
[ details elided ]
ok, then there's a bug in the driver. you be able to just close the
device, and then reopen it with new parameters. unloading the modules
should not be necessary. as i said, we don't allow reset of the
parameters while the card is open for PCM because moving to 96kHz
changes many aspects of how the h/w needs to be controlled & used, too
many to reasonably keep track of. remember: 48<->96 over S/PDIF is
simple; the same transition for ADAT will always involve a hack
because ADAT doesn't allow 96 natively.
--p
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