[alsa-devel] fsl_ssi.c: Getting channel slips with fsl_ssi.c in TDM (network) mode.

[Nicolin Chen]

On Fri, Oct 30, 2015 at 09:29:02AM +0100, arnaud.mouiche at invoxia.com wrote:

> At imx50 age, I remember one workaround was to fill the fifo
> manually, writing directly a number of samples (equal to the number
> of slots for one frame to keep the synchronization), and then,
> enable the TMDAE.
> This just allow to not have to wait an undefined period of time for
> the DMA to be ready.
> But, on the other hand, if the time to wait the DMA is short enough,
> it should not be an issue.

Nice input. This reminds me of the zero-filling step inside the
ESAI startup procedure:

	case SNDRV_PCM_TRIGGER_START:
	case SNDRV_PCM_TRIGGER_RESUME:
	case SNDRV_PCM_TRIGGER_PAUSE_RELEASE:
		regmap_update_bits(esai_priv->regmap, REG_ESAI_xFCR(tx),
				   ESAI_xFCR_xFEN_MASK, ESAI_xFCR_xFEN);

		/* Write initial words reqiured by ESAI as normal procedure */
		for (i = 0; tx && i < channels; i++)
			regmap_write(esai_priv->regmap, REG_ESAI_ETDR, 0x0);

		regmap_update_bits(esai_priv->regmap, REG_ESAI_xCR(tx),
				   tx ? ESAI_xCR_TE_MASK : ESAI_xCR_RE_MASK,
				   tx ? ESAI_xCR_TE(pins) : ESAI_xCR_RE(pins));
		break;

It's exactly the same thing to prevent underrun. This might be
a reasonable alternative option due to no polling overhead and
timeout handling.

Thanks
Nicolin