[alsa-devel] ASoC: at91sam9260-PCM1808/TAS5709-based board driver

[Mark Brown]

On Tue, Aug 25, 2009 at 01:31:57PM -0400, Pedro I. Sanchez wrote:

> The TAS5709 is a playback-slave-only device The SSC is therefore put in 
> master mode and I can see the SSC clock signals (SCLK and LRCLK) on the 
> scope when playing a sound file. I can also see the activity on the data 
> line. But unfortunately, there is no sound, just a speaker Hisss when I 
> play a file. I doubled checked all the volume levels to ensure they are 
> not mutted.

Is there any control in the CODEC?  If so you should check that it is
set up properly.

> However, I noticed that the duty cycle of the SSC clocks is not 50% as I 
> would expect it to be. There seem to be much more bits on one channel 
> than in the other (my sample file is stereo, 16 bits, 44.1 MHz). The 
> sample clock illustrations in the TAS5709 all have the same number of 
> bits per channel, but it doesn't say explicitly that this is mandatory. 
>  From my understanding of the I2S spec, this is not.

> The TAS5709 is supposed to detect the clock and data rates 
> automatically. Do you know if this non-50% duty cycle could be the 
> reason for the lack of sound? Is there a way to force it to be 50%?

If the CODEC is trying to work out what the sample and clock rates are
automatically then it does seem reasonable that any oddities in the
clocks that it's given might confuse it somehow - for example, causing
it to expect more bit clocks than it's actually getting which would
cause it to fail to clock in enough data to do a conversion.

I'd expect that appropriate configuration of the clock dividers for the
SSC it's possible to make it generate more normal looking clocks, I
don't think anyone ever optimised the divider configuration when the
AT91SAM9G20-EK was running the SSC in master mode.