[sdiy] STM32 vs WM8731

[Rob Spencer]

For some reason STM32CubeMx doesn’t seem to like anything lower that 1000x the sample rate…

https://www.dropbox.com/s/a22vmj9t1szljzr/Screenshot%202016-02-17%2018.50.11.png?dl=0

https://www.dropbox.com/s/mr0a1erzbs1tmo6/Screenshot%202016-02-17%2018.51.15.png?dl=0

Rob Spencer
gmsn.co.uk
07590 267835




On 17/02/2016 18:14, "Synth-diy on behalf of Eric Brombaugh" <synth-diy-bounces at dropmix.xs4all.nl on behalf of ebrombaugh1 at cox.net> wrote:

The I2S master clock output from the STM32 will only be present when the 
I2S port is active. You need to have the peripheral fully configured and 
DMA running before you see any traffic on the I2S signals.

I generally wait until after the I2S port is up and running before 
trying to issue commands on the I2C control port. I'm not 100% certain 
that this is necessary in all cases, but the WM8731 does some adaptive 
configuration based on the command setup and the measurements it does of 
the incoming I2S clock ratios, so it's best to have all the information 
present when you command it.

The frequency and hence visibility of the MCK signal depends on what 
oversampling ratio you've chosen. For a typical 48ksps sample rate with 
a 256x oversample ratio the MCK should be about 12.288MHz which should 
be well within your equipment's capability. You can run the codec at 64x 
and 128x as well, so it's possible you could get an MCK of less than 
20MHz even if you're running at 192ksps.

Eric

On 02/17/2016 11:00 AM, Rob Spencer wrote:
 I think I’m getting to the crux of the issue.

 Am I right in thinking I2S MCK is only active when sending data across I2S? So if it’s in DMA mode, it will be active.

 And without MCK or it’s own clock, the CODEC can’t ACK the I2C traffic?

 I’m also working on the assumption that I can’t measure MCK as it’s over the 20MHz limit of my scope and logic analyser.


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