[alsa-devel] Bug? Sound support for at91sam9x5-wm8731 based boards

[Richard Genoud]

2013/11/20 Richard Genoud <richard.genoud at gmail.com>:
> [added Nicolas Ferre and Bo Shen ]
>
> 2013/11/19 Zhong Li <zql at glomationinc.com>:
>>
>> One of the testing hardware is the Atmel at91sam9g25-ek (the CPU module and the carrier board).  We tried both the 2.6.39 patched with the Atmel patches and the mainline 3.12-rc.  The command to test the sound is just the simple aplay <sound-test-file>.  The wav file is available here, https://drive.google.com/file/d/0B3TSFX4Mq9PoeTdJOGVaZk5rTWM/edit?usp=sharing.
>>
>> Thanks
>
> Ok, I reproduce the bug on g35-ek with a v3.11.7+(sam9x5 sound patches) kernel
>
> So, *sometimes*,  the left and right channel are swapped. ( I found
> also the ratio 1 out of 6 (but once it has happened, it seems to be
> more often))
> I tested that with the file given by Zhong Li, and with a file I
> created with audacity (440Hz only on right channel).
> I could see at the scope that the channels are swapped before the
> w8731 codec (the data on the TD line are sometime on the low edge of
> TF, instead of always being on the high edge (I2S mode)).
> There's, in both cases, a clock period (TK) between the rising/falling
> edge of TF and the 1st data bit on TD, so the mode is always I2S, and
> the channel data are swapped.
>
> I'll try to have a look (but I don't have much time right now)
>
> If someone could test that on a sam9g20 or a WM8904 based board, since
> they share the same DAI format, they may have the same problem.

After reading the sources (mainly sound/soc/atmel/atmel_ssc_dai.c), I
don't understand how the right and left channel are synchronized.
(which one will be on TF rising edge, and which one on TF falling edge
?)
In the SSC_TCMR register, the start event is TF_FALLING when there
only one channel (i.e. mono source always on left channel)
With a stereo source, it's TF_EDGE (Detection of any edge on TF
signal) ; so the samples are transferred on rising and falling edge.
I didn't see anything in the SSC what could synchronize the first
sample with a TF falling edge.
Or I missed something ?

Nicolas, Bo, any idea ?

Richard.