[alsa-devel] Channel swapping problem on Atmel SSC audio

[Irfan Shaikh]

I had faced the similar issue on IMx31. The cause there was reversal of LRCK clock {180 degree phase shift}.
probing the LRCK clock may help you to find the problem

________________________________________
From: alsa-devel-bounces at alsa-project.org [alsa-devel-bounces at alsa-project.org] On Behalf Of Patrick Ziegler [patrick.ziegler at fh-kl.de]
Sent: Friday, November 12, 2010 1:36 PM
To: alsa-devel at alsa-project.org
Cc: Ryan Mallon
Subject: Re: [alsa-devel] Channel swapping problem on Atmel SSC audio

Am 11.11.2010 13:27, schrieb Alan Horstmann:
> On Wednesday 10 November 2010 22:49, Ryan Mallon wrote:
>
>> I'm working on a custom board using the AT91SAM9G45 processor and a
>> TLV320AIC26 SPI attached audio codec using I2S format audio. When doing
>> audio playback on the board the left and right channels are occasionally
>> flipped.
>>
> <snip>
>
>
>> Has anybody else had this problem, or does anybody have any AT91/Atmel
>> hardware that they could test to see if it occurs on other hardware also?
>>
> I have worked with the AT91SAM9260 on a project which is currently suspended
> (other priorities), where we had a simiar problem, with a codec on SPI.
> Every time audio was started (capture or playback) the channels could be
> swapped.  Solving that issue remains TODO when we restart.
>
> There was a thread on alsa-devel last month 'Soc Atmel SSC stereo problem'
> with some suggestions.
>
>
In the thread mentioned, Alan proposed me amongst other things to test
the LRCK level before starting the SSC. This works well for me. Maybe it
should be implemented in a more generic way but the following
modification does the trick for me.

in function  atmel_pcm_trigger inside file sound/soc/atmel/atmel-pcm.c :

case SNDRV_PCM_TRIGGER_START:
+while(!at91_get_gpio_value(AT91_PIN_PB12));
+while(at91_get_gpio_value(AT91_PIN_PB12));

case SNDRV_PCM_TRIGGER_RESUME:
+while(!at91_get_gpio_value(AT91_PIN_PB12));
+while(at91_get_gpio_value(AT91_PIN_PB12));

Patrick

--

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