[alsa-devel] atmel SSC DSP A mode

[Codrin.Ciubotariu at microchip.com]

On 03.06.2019 13:19, Willem Romkes wrote:
> 
> *
> *
> 
> Hi,
> 
> We are using linux-at91 and lately I have been working on adding support 
> for a custom soundcard, a dual tlv320aic3x codec on SAMA5D3 platform. 
> This soundcard uses DSP A mode.
> 
> We are facing audio issues: When we playback a WAV file with a sine 
> wave, the codec outputs far from a clean sine wave. The problem I think 
> is that the CKI settings for the TMCR register isn't set correctly. 
> see commit 20cf2603b122bf71fb54def1de6a2ad73d5ddb0b
> Author: Bo Shen <voice.shen at atmel.com>
> Date:   Fri Jan 30 17:38:42 2015 +0800
> 
>      ASoC: atmel_ssc_dai: fix the setting for DSP mode
> 
>      When SCC work in DSP A mode, the data outputs/inputs are shift out on
>      falling edge, the frame sync are sample on the rising edge.
> 
>      Reported-by: Songjun Wu <songjun.wu at atmel.com>
>      Signed-off-by: Bo Shen <voice.shen at atmel.com>
>      Signed-off-by: Mark Brown <broonie at kernel.org>
> 
> diff --git a/sound/soc/atmel/atmel_ssc_dai.c 
> b/sound/soc/atmel/atmel_ssc_dai.c
> index e691aab..35e44e4 100644
> --- a/sound/soc/atmel/atmel_ssc_dai.c
> +++ b/sound/soc/atmel/atmel_ssc_dai.c
> @@ -502,7 +502,7 @@ static int atmel_ssc_hw_params(struct 
> snd_pcm_substream *substream,
>                  rcmr =    SSC_BF(RCMR_PERIOD, ssc_p->rcmr_period)
>                          | SSC_BF(RCMR_STTDLY, 1)
>                          | SSC_BF(RCMR_START, SSC_START_RISING_RF)
> -                       | SSC_BF(RCMR_CKI, SSC_CKI_RISING)
> +                       | SSC_BF(RCMR_CKI, SSC_CKI_FALLING)
>                          | SSC_BF(RCMR_CKO, SSC_CKO_NONE)
>                          | SSC_BF(RCMR_CKS, SSC_CKS_DIV);
> 
> @@ -517,7 +517,7 @@ static int atmel_ssc_hw_params(struct 
> snd_pcm_substream *substream,
>                  tcmr =    SSC_BF(TCMR_PERIOD, ssc_p->tcmr_period)
>                          | SSC_BF(TCMR_STTDLY, 1)
>                          | SSC_BF(TCMR_START, SSC_START_RISING_RF)
> -                       | SSC_BF(TCMR_CKI, SSC_CKI_RISING)
> +                       | SSC_BF(TCMR_CKI, SSC_CKI_FALLING)
>                          | SSC_BF(TCMR_CKO, SSC_CKO_CONTINUOUS)
>                          | SSC_BF(TCMR_CKS, SSC_CKS_DIV);
> 
> @@ -546,7 +546,7 @@ static int atmel_ssc_hw_params(struct 
> snd_pcm_substream *substream,
>                  rcmr =    SSC_BF(RCMR_PERIOD, 0)
>                          | SSC_BF(RCMR_STTDLY, START_DELAY)
>                          | SSC_BF(RCMR_START, SSC_START_RISING_RF)
> -                       | SSC_BF(RCMR_CKI, SSC_CKI_RISING)
> +                       | SSC_BF(RCMR_CKI, SSC_CKI_FALLING)
>                          | SSC_BF(RCMR_CKO, SSC_CKO_NONE)
>                          | SSC_BF(RCMR_CKS, ssc->clk_from_rk_pin ?
>                                             SSC_CKS_PIN : SSC_CKS_CLOCK);
> 
> For both the TCMR and RCMR the CKI is set to SSC_CKI_FALLING, but I 
> think for the TCMR the CKI should be set to SSC_CKI_RISING. See datasheet:
> 
> TCMR CKI: "1: The data outputs (Data and Frame Sync signals) are shifted 
> out on Transmit Clock rising edge. The Frame sync signal
> input is sampled on Transmit clock falling edge."
> 
> RCMR CKI: "0: The data inputs (Data and Frame Sync signals) are sampled 
> on Receive Clock falling edge. The Frame Sync signal out-
> put is shifted out on Receive Clock rising edge."
> 
> Setting the CKI in TCMR to SSC_CKI_RISING to fixes our issues.

Hi Willem,

It this DS of the codec you are using?
http://www.ti.com/lit/ds/symlink/tlv320aic33.pdf

Are you using the DSP mode described in figure 25 DSP Serial Bus Mode 
Operation? If yes, then you should use the DSP_B mode...

Thanks and best regards,
Codrin