clocks on xvf3000 reference design

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pisljar
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clocks on xvf3000 reference design

Postby pisljar » Mon Jul 17, 2017 1:39 pm

Hello,

looking at the reference design i have a few questions regarding clocks:
- Si5351A is used to generate 3 clocks:
-- 32K (seems to be used for wifi module ?)
-- 24M for xvf3000
-- 24.576 low jitter master clock used for MCLK_DAC, MCLK_TILE1 and MCLK

it also mentions that clock speeds are docuented in the software manual, but its not available yet, so i am wondering:

- what are the MCLK_TILE1 and MCLK clocks used for ?
- is it possible to omit them (can XVF generate them ? or are they only needed for part of functionality ?)


some additional questions i have:
- how important are the clock buffers ? possible to omit them ?

- whats the FB1 used for ? how important is it and is it possible to omit it ?

- what about NC7WZ07 ? can it be omitted ? can it be replaced with something simpler ?


thanks a lot, looking forward to your reply
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infiniteimprobability
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Postby infiniteimprobability » Wed Jul 19, 2017 11:42 am

- what are the MCLK_TILE1 and MCLK clocks used for ?

MCLK on tile[0] is used to clock a clockblock which then prescales by 8 to provide the PDM clock for the mics. 24.576->3.072MHz
MCLK_TILE1 provides a copy of the master clock for USB audio cases which is used in the explicit feedback calculation for the isochronous endpoints.
It is also used to generate the BCLK and LRCLK in the USB audio case to clock the DAC

- is it possible to omit them (can XVF generate them ? or are they only needed for part of functionality ?)

You need a PDM clock (3.072M) somehow and the on-board DAC needs an MCLK to work properly. You could probably get rid of the connection to tile[1] with some additional effort but I don't think you can delete it altogether.

some additional questions i have:
- how important are the clock buffers ? possible to omit them ?

Maybe, if you had a series resistor per trace and the traces were all matched in length. MUltiple reflections at different times due to unmatched clock tree wouldn't be nice.. This is probably a question more for Silicon Labs than XMOS..

- whats the FB1 used for ? how important is it and is it possible to omit it ?

It's a performance optimisation to reduce noise. If you FFT the output from the mics it's possible to see the switching supply noise (~1.5MHz) so it's there to reduce that influence. Again, probably a question for your PDM mic vendor..

- what about NC7WZ07 ? can it be omitted ? can it be replaced with something simpler ?

The XTAG debug adapter has a push pull drive so something is needed to allow the reset to be shared with POR. If you want to go super-cheap maybe a schottky diode..
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infiniteimprobability
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Postby infiniteimprobability » Wed Jul 19, 2017 12:31 pm

-- 32K (seems to be used for wifi module ?)


Correct - unused in the current reference design

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