How does this tie in with sample rate triplets?
you may remember the struggles I have a few months ago with sample rate
triplet parsing. At the time I considered splitting it into two virtual
clocks. Reading this I'm glad I didn't.
The DAC I make has two physical clocks which are chosen by firmware
depending on which sample rate is requested by the driver. So the firmware
only exposes one clock to the driver. Let me know if you need code and
descriptors, both are open source in my case.
Possibly OT: Before the Win10 UAC2 driver came out, all other OSes with
UAC2 allowed for very relaxed sample sample rate triplet parsing. I.e.
triplets could come in an arbitrary sequence, and available rates came out
of some sort() which followed some sort of parse(). That was the world in
which our firmware was tested and found to be solid. Less strict parsing -
and allowing out-of-sequence triplets will make the Win10 UAC2 driver
compatible with more hardware which is already in the field.
Best,
Børge
On Thu, Jan 11, 2018 at 9:14 AM, Franz Detro <
franz.detro@xxxxxxxxxxxxxxxxxxxxx> wrote:
KS wrote:
In USB2 Audio, it is possible for device to support multiple clock
source that can be selected through a clock selector.
I don't see that anywhere in the Audio Class specification. Where is
that described?
Audio20 final.pdf, 3.13.11.2 Clock Selector, 3.16.3 Clock Model, 4.7.2.1
Clock Source Descriptor and 4.7.2.2 Clock Selector Descriptor
The Audio Class driver should extract clock information from the UAC
descriptors and provide a GUI to select a clock (in case of multiple
clocks) / configure the sample rate.
In case of externally driven clocks the driver should monitor an
eventually existing interrupt notification endpoint for changes of current
clock (clock selector) and sample rate.
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In Mac OS, there is a droplist in audio MIDI app that allow user to
select the desired clock source.
What choices do you see?
--
Tim Roberts, timr@xxxxxxxxx
Providenza & Boekelheide, Inc.
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