[alsa-devel] [PATCH 2/2] ALSA: core: group read of pointer, tstamp and jiffies

[Takashi Iwai]

At Tue, 22 May 2012 14:54:02 -0500,
Pierre-Louis Bossart wrote:
> 
> Group read of hw_ptr, tstamp and jiffies in a sequence
> for better correlation. Previous code took timestamp at the
> end, which could introduce delays between audio time and
> system time.
> 
> Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart at linux.intel.com>

Applied this one.  Thanks.


Takashi

> ---
>  sound/core/pcm_lib.c |   23 ++++++++++++++++++-----
>  1 files changed, 18 insertions(+), 5 deletions(-)
> 
> diff --git a/sound/core/pcm_lib.c b/sound/core/pcm_lib.c
> index ae46d75..3f3097d 100644
> --- a/sound/core/pcm_lib.c
> +++ b/sound/core/pcm_lib.c
> @@ -313,9 +313,22 @@ static int snd_pcm_update_hw_ptr0(struct snd_pcm_substream *substream,
>  	snd_pcm_uframes_t old_hw_ptr, new_hw_ptr, hw_base;
>  	snd_pcm_sframes_t hdelta, delta;
>  	unsigned long jdelta;
> +	unsigned long curr_jiffies;
> +	struct timespec curr_tstamp;
>  
>  	old_hw_ptr = runtime->status->hw_ptr;
> +
> +	/*
> +	 * group pointer, time and jiffies reads to allow for more
> +	 * accurate correlations/corrections.
> +	 * The values are stored at the end of this routine after
> +	 * corrections for hw_ptr position
> +	 */
>  	pos = substream->ops->pointer(substream);
> +	curr_jiffies = jiffies;
> +	if (runtime->tstamp_mode == SNDRV_PCM_TSTAMP_ENABLE)
> +		snd_pcm_gettime(runtime, (struct timespec *)&curr_tstamp);
> +
>  	if (pos == SNDRV_PCM_POS_XRUN) {
>  		xrun(substream);
>  		return -EPIPE;
> @@ -343,7 +356,7 @@ static int snd_pcm_update_hw_ptr0(struct snd_pcm_substream *substream,
>  		delta = runtime->hw_ptr_interrupt + runtime->period_size;
>  		if (delta > new_hw_ptr) {
>  			/* check for double acknowledged interrupts */
> -			hdelta = jiffies - runtime->hw_ptr_jiffies;
> +			hdelta = curr_jiffies - runtime->hw_ptr_jiffies;
>  			if (hdelta > runtime->hw_ptr_buffer_jiffies/2) {
>  				hw_base += runtime->buffer_size;
>  				if (hw_base >= runtime->boundary)
> @@ -388,7 +401,7 @@ static int snd_pcm_update_hw_ptr0(struct snd_pcm_substream *substream,
>  		 * Without regular period interrupts, we have to check
>  		 * the elapsed time to detect xruns.
>  		 */
> -		jdelta = jiffies - runtime->hw_ptr_jiffies;
> +		jdelta = curr_jiffies - runtime->hw_ptr_jiffies;
>  		if (jdelta < runtime->hw_ptr_buffer_jiffies / 2)
>  			goto no_delta_check;
>  		hdelta = jdelta - delta * HZ / runtime->rate;
> @@ -430,7 +443,7 @@ static int snd_pcm_update_hw_ptr0(struct snd_pcm_substream *substream,
>  	if (hdelta < runtime->delay)
>  		goto no_jiffies_check;
>  	hdelta -= runtime->delay;
> -	jdelta = jiffies - runtime->hw_ptr_jiffies;
> +	jdelta = curr_jiffies - runtime->hw_ptr_jiffies;
>  	if (((hdelta * HZ) / runtime->rate) > jdelta + HZ/100) {
>  		delta = jdelta /
>  			(((runtime->period_size * HZ) / runtime->rate)
> @@ -492,9 +505,9 @@ static int snd_pcm_update_hw_ptr0(struct snd_pcm_substream *substream,
>  	}
>  	runtime->hw_ptr_base = hw_base;
>  	runtime->status->hw_ptr = new_hw_ptr;
> -	runtime->hw_ptr_jiffies = jiffies;
> +	runtime->hw_ptr_jiffies = curr_jiffies;
>  	if (runtime->tstamp_mode == SNDRV_PCM_TSTAMP_ENABLE)
> -		snd_pcm_gettime(runtime, (struct timespec *)&runtime->status->tstamp);
> +		runtime->status->tstamp = curr_tstamp;
>  
>  	return snd_pcm_update_state(substream, runtime);
>  }
> -- 
> 1.7.6.5
>