Re: [PATCH 2/2] ASoc: wm8731: add normal mode with 12MHz XTAL

[Matt Flax <flatmax@flatmax.org>]

OK - I will look into that futher. Thanks for the info.

Is it possible to look at patch 1/2 in this series ?

thanks
Matt

On 13/06/16 21:59, Charles Keepax wrote:
> On Mon, Jun 13, 2016 at 07:45:22PM +1000, Matt Flax wrote:
>> On 13/06/16 18:37, Charles Keepax wrote:
>>> On Sun, Jun 12, 2016 at 01:22:26PM +1000, Matt Flax wrote:
>>>> It appears that my logic here is flawed.
>>>>  From what I can tell, it isn't possible to get a suitable bit clock out of
>>>> the codec when using a 12 MHz crystal. For that reason, in my hardware I
>>>> will change crystals from 12 MHz.
>>> This looks correct the chip only has simple dividers so you won't
>>> be able to get a good audio rate clock from a 12MHz crystal.
>>>
>>>> I just want to check ... are there any versions of this codec which output
>>>> the bit clock when in USB mode on the BCLK pin ?
>>>>
>>> Apologies I am not quite sure I follow what USB mode is in this
>>> context, and the bit clock surely always comes out of the BCLK
>>> pin. Do you simply mean a system with a clock speed that
>>> relates to the 48MHz USB clock, such as your 12MHz? Basically any
>>> part that has a PLL/FLL should work for that, for example the
>>> wm8998:
>>>
>>> http://www.cirrus.com/en/products/pro/detail/P1265.html
>> Literally, with the chip set to usb mode (register 0b0001000 bit 0, page 41
>> of the data sheet) it appears that the 12 MHz clock comes out of the BCLK
>> pin, rather then the bit clock.
> Ah seems there are two versions of the chip the MC and L I was
> looking at the datasheet for the version that doesn't have that
> mode.
>
>  From that datasheet it looks like it should be possible to
> support audio rate clocks from a 12MHz input. Although as you say
> the 44.1 clock is not exactly 44.1. I am not sure why you are
> getting 12MHz coming out of the BCLK pin the datasheet certainly
> does not appear to suggest this should happen. Are you sure the
> sample rate and clock divider registers are set sensibly? My
> first guess would be if things are in an unsupported state then
> perhaps it just fires the clock straight through. I assume we are
> very sure the input clock is 12MHz? Only other thing I can
> imagine is for some reason we have a higher clock rate than we
> expected and on the scope it would be hard to differenciate
> between 12.288MHz and 12MHz dead. So for example if it was a
> 48MHz USB clock coming in rather than 12, then the chip tries to
> generate a 3.072MHz bit clock that would look like 12MHz.
>
> Again I guess a newer part with an PLL might be simpler as you
> can simply use the PLL to generate audio rate clocks from the
> 12MHz.
>
> Thanks,
> Charles
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