[alsa-devel] WM8731 using I2S on omap3 McBSP2 issues

Peter Ujfalusi peter.ujfalusi at nokia.com
Fri Sep 25 08:03:06 CEST 2009


On Thursday 24 September 2009 20:06:07 ext Rick Bronson wrote:
> Hi,
>   I'm working on getting a WM8731 (in SLAVE) working using I2S on
> omap3 McBSP2 (in MASTER).

> static int omap3csb740_hw_params(struct snd_pcm_substream *substream,
> ...
>  ret = snd_soc_dai_set_fmt(codec_dai, SND_SOC_DAIFMT_I2S |
>  ret = snd_soc_dai_set_fmt(cpu_dai,  SND_SOC_DAIFMT_I2S |
>  ret = snd_soc_dai_set_sysclk(codec_dai, 0, 12288000,   SND_SOC_CLOCK_IN);
>  ret = snd_soc_dai_set_sysclk(cpu_dai, OMAP_MCBSP_SYSCLK_CLKS_EXT, 0,

I think the problem is here.
The MCBSP_CLKS pin is connected to CLK256FS pin of TWL4030 (or TPA).
Since you are not using the TWL codec, there will be no clock on the MCBSP_CLKS 
pin, thus no functional clock for McBSP, thus no bits are shifted in or out.
You can try to use the internal functional clock:

  ret = snd_soc_dai_set_sysclk(cpu_dai, OMAP_MCBSP_SYSCLK_CLKS_FCLK, 0,

Than set the correct divider, which depends on the frequency you would like to 
play. The source for the CLKS_FCLK is (in case of McBSP2) PER_96M_FCLK, so 
96MHz. Now you have to divide this to get the correct value, as I recall quite a 
long time ago there were some discussion about this here, and I have sent some 
'formula' to calculate it, but I can not find it now :(

>  ret = snd_soc_dai_set_clkdiv(cpu_dai, OMAP_MCBSP_CLKGDV, 256);
>   Any help is greatly appreciated.
>   Rick Bronson


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