[sdiy] Digital Audio CODEC config help

[Richie Burnett]

Hi guys and girls,

I'm after a bit of help with configuring an audio CODEC for a DIY project...

In the true spirit of surviving the chip shortage I've carefully de-soldered 
three AK4556 3V 192kHz 24-bit audio CODEC chips from an obsolete DSP board. 
And I now want to put one of them to use for experimenting with digital 
audio in and out of a Kinetis KL26 (Cortex M0+ based) micro development 
board.  The micro has a Serial Audio Interface peripheral and I've 
configured it to give me 24-bit stereo audio in and out in left-justified 
format at 96kHz.  All the timings looks good when waveforms are checked with 
a scope, and looks exactly like other times I've done this sort of thing 
with SHARC, dsPIC, etc.

MCLK = 24.576 MHz
BCLK = 6.144 MHz
WCLK = 96 kHz

The problem I am having is figuring out how to configure the CODEC chip. 
(Datasheet link below...)

https://upverter.com/datasheet/ae3c782f80d262f78bae1b98785ec24c3267bc44.pdf

Under the "features" section on the first page of the datasheet it says that 
it can do a sampling rate of 54kHz to 108kHz in "Double Speed" mode with the 
MCLK being 256xFs.  This sounds perfect for my intended 96kHz sample rate 
and the math fits.  However, looking at Table 3 on page 15 it seems unclear 
to me which "Mode" I want.  I've narrowed it down a bit because the CODEC 
will be a slave.  And further narrowed it down to modes 8-11 because I want 
left-justified data in and out.  And we can assume that I want the ADC 
dc-blocking HPF filter on, so that brings the choice down to Mode 8 or Mode 
9.  This is where I get stuck.  Both seem to offer 256Fs as a MCLK 
multiplier, but the 256Fs option in Mode 8 is marked "Double speed" and the 
256Fs option for Mode 9 is marked "Normal Speed".  I guess from this that I 
need Mode 9 because the info on the first page said 54-108kHz is supported 
in Double Speed?

Maybe I'm being dumb and just getting confused.  I've done this sort of 
thing before for other CODECs (Cirrus Crystal) and the datasheets normally 
had included a table of example clock rates and sample rates, and explicitly 
said what configuration is required for typical audio sample rates with 
different MCLK frequencies.  The AKM datasheet just seems to present the 
data differently.

Any guidance would be much appreciated!  I haven't tried implementing any 
combinations yet, because I would ideally like to know that I've chosen the 
config right, so that if it doesn't work or I get mangled audio I can assume 
it's a signal integrity issue and go about shortening flying leads, 
termination, etc. ;-)

Thanks,

-Richie,