Re: [alsa-devel] alsa timestamps

20 Nov 2007


      Takashi Iwai kirjoitti:
...
At Tue, 20 Nov 2007 16:54:32 +0200,
Heikki Lindholm wrote:
...
Takashi Iwai kirjoitti:
...
At Mon, 19 Nov 2007 15:41:46 +0200,
Heikki Lindholm wrote:
...
Jaroslav Kysela kirjoitti:
...
On Mon, 19 Nov 2007, Heikki Lindholm wrote:
...
Heikki Lindholm kirjoitti:
> Hello list,
>
> I took up some old dusty code of mine that uses snd_pcm_state followed 
> by snd_pcm_status_get_tstamp when in capture mode. The code used to 
> work, but now the returned timestamps are all zeroes. Is there some API 
> change done recently or is the whole timestamping deprecated or 
> something? I've tried with different drivers on ubuntu's alsa .14 and 
> gentoo's .14. I've also tried mmap'ed and r/w modes, and I'm setting the 
> TSTAMP_MMAP sw param.
I figured out that this doesn't happen when using hw:x,y devices. Is it 
a documented feature that some (software?) devices don't fill in timestamps?
I think that it should be fixed. Could you send us 'snd_pcm_dump()' for a 
non-working device? It's probably ommited code in direct pcm plugins (dmix 
& etc.).
Here goes. The driver is snd_aoa. It seems as if the timestamp mode 
isn't propagated to the hw device.
AFAIK, the time-stamp mode isn't handled properly with direct plugins
because of its nature.  Since the direct plugins share the same PCM
hardware instance with multiple processes, you cannot change the
parameter arbitrarily from a single client.
We may implement an emulation in alsa-lib instead, though...
For the time being, is there any other way of determining whether a pcm 
supports time stamps than just trying out and seeing if zero is all that 
comes out?
Hmm, at the second look at the dmix/dsnoop code, it has some lines
that actually update the timestamp value (as emulation).  So,
basically it should work.  Maybe some other parts are broken...
Do you have a small test case code just for checking?
Attached a test case that I just wrote. Seems I need it anyway since 
drivers are acting bogus, too. On a Power Mac G5, using snd_aoa, running 
the program with
./alsatest hw:0,0 1024
produces good timestamps whereas running with
./alsatest default 1024
produces zeros (the second param is period size).
I also observed the same behaviour on a bog standard x86, with SB Live, 
I think..
-- Heikki Lindholm
#include <stdio.h>
#include <stdint.h>
#include <alsa/asoundlib.h>
#define FORMAT SND_PCM_FORMAT_S16_BE
#define RATE 48000
int main(int argc, char *argv[]) {
    snd_pcm_t *handle;
    snd_pcm_hw_params_t *params;
    snd_pcm_sw_params_t *swparams;
    snd_pcm_uframes_t period_size;
    snd_pcm_uframes_t buffer_size;
    snd_pcm_status_t *status;
    uint8_t *buf;
    int rate;
    int ret;
    ssize_t r;
    int t;
if ((ret = snd_pcm_open(&handle, argv[1], 
    		SND_PCM_STREAM_CAPTURE, 0)) < 0) {
    	goto out;
    }
snd_pcm_hw_params_alloca(&params);
    snd_pcm_sw_params_alloca(&swparams);
    if ((ret = snd_pcm_hw_params_any(handle, params)) < 0) {
    	goto out;
    }
    if ((ret = snd_pcm_hw_params_set_access(handle,
    		params, SND_PCM_ACCESS_RW_INTERLEAVED)) < 0) {
    	goto out;
    }
    if ((ret = snd_pcm_hw_params_set_format(handle, params, 
    		FORMAT)) < 0) {
    	goto out;		
    }
    if ((ret = snd_pcm_hw_params_set_channels(handle,
    		params, 2)) < 0) {
    	goto out;
    }
    rate = RATE;
    if ((ret = snd_pcm_hw_params_set_rate_near(handle, params,
    		&rate, 0) < 0)) {
    	goto out;
    }
    period_size = atoi(argv[2]);
    if ((ret = snd_pcm_hw_params_set_period_size_near(handle, params,
    		&period_size, 0)) < 0) {
    	fprintf(stderr, "failed to set period size.\n");
    }
    t = 1000000;
    if ((ret = snd_pcm_hw_params_set_buffer_time_near(handle, params,
    		&t, 0)) < 0) {
    	fprintf(stderr, "failed to set buffer time.\n");
    }
    if ((ret = snd_pcm_hw_params(handle, params)) < 0) {
    	goto out;
    }
    snd_pcm_hw_params_get_period_size(params, &period_size, 0);
    snd_pcm_hw_params_get_buffer_size(params, &buffer_size);
snd_pcm_sw_params_current(handle, swparams);
    if ((ret = snd_pcm_sw_params_set_tstamp_mode(handle, swparams,
    		 SND_PCM_TSTAMP_MMAP)) < 0) {
    	goto out;
    }
    if ((ret = snd_pcm_sw_params(handle, swparams)) < 0) {	
    	goto out;
    }
    if ((ret = snd_pcm_prepare(handle)) < 0) {
    	goto out;
    }
buf = malloc(period_size*2*2);
snd_pcm_status_alloca(&status);
    for (t = 0; t < 1000; t++) {
    	r = snd_pcm_readi(handle, buf, period_size);
    	if (snd_pcm_status(handle, status) < 0) {
    		fprintf(stderr, "snd_pcm_status failed.\n");
    	}
    	else {
    		snd_htimestamp_t tstamp;
    		snd_pcm_status_get_htstamp(status, &tstamp);
    		printf("time: %d %d\n", tstamp.tv_sec, tstamp.tv_nsec);
    	}
    }
snd_pcm_close(handle);
out:
    return 0;
}