[pulseaudio-discuss] [PATCH] alsa: get avail, delay, timestamps in a single kernel call

[Pierre-Louis Bossart]

> sorry for the long delay.

no worries. looks like this mailing list went back 4 months in time with 
the switch from Daylight Savings time?

> This seems to make a lot of sense, but a question - does this impose a
> requirement on a certain version of alsa-lib and/or the linux kernel?

no, these changes are using standard calls.
The changes I pushed at the kernel level since my presentation at the 
Plumbers conference will require a specific version of alsa-lib to read 
the audio timestamps, everything below should work right off the bat 
without dependencies.

> 2012-07-30 02:46, Pierre-Louis Bossart skrev:
>> Refactor code to fetch avail, delay and timestamp values
>> in a single call to snd_pcm_status().
>> The information reported is exactly the same as before,
>> however it is extracted in a more atomic manner to
>> improve timer-based scheduling.
>>
>> Signed-off-by: Pierre-Louis Bossart
>> <pierre-louis.bossart at linux.intel.com>
>> ---
>>   src/modules/alsa/alsa-sink.c   |   12 ++++--------
>>   src/modules/alsa/alsa-source.c |   12 ++++--------
>>   src/modules/alsa/alsa-util.c   |   17 ++++++++++++-----
>>   src/modules/alsa/alsa-util.h   |    2 +-
>>   4 files changed, 21 insertions(+), 22 deletions(-)
>>
>> diff --git a/src/modules/alsa/alsa-sink.c b/src/modules/alsa/alsa-sink.c
>> index 544399e..e4baa1f 100644
>> --- a/src/modules/alsa/alsa-sink.c
>> +++ b/src/modules/alsa/alsa-sink.c
>> @@ -825,6 +825,7 @@ static void update_smoother(struct userdata *u) {
>>       int err;
>>       pa_usec_t now1 = 0, now2;
>>       snd_pcm_status_t *status;
>> +    snd_htimestamp_t htstamp = { 0, 0 };
>>       snd_pcm_status_alloca(&status);
>> @@ -833,18 +834,13 @@ static void update_smoother(struct userdata *u) {
>>       /* Let's update the time smoother */
>> -    if (PA_UNLIKELY((err = pa_alsa_safe_delay(u->pcm_handle, &delay,
>> u->hwbuf_size, &u->sink->sample_spec, FALSE)) < 0)) {
>> +    if (PA_UNLIKELY((err = pa_alsa_safe_delay(u->pcm_handle, status,
>> &delay, u->hwbuf_size, &u->sink->sample_spec, FALSE)) < 0)) {
>>           pa_log_warn("Failed to query DSP status data: %s",
>> pa_alsa_strerror(err));
>>           return;
>>       }
>> -    if (PA_UNLIKELY((err = snd_pcm_status(u->pcm_handle, status)) < 0))
>> -        pa_log_warn("Failed to get timestamp: %s",
>> pa_alsa_strerror(err));
>> -    else {
>> -        snd_htimestamp_t htstamp = { 0, 0 };
>> -        snd_pcm_status_get_htstamp(status, &htstamp);
>> -        now1 = pa_timespec_load(&htstamp);
>> -    }
>> +    snd_pcm_status_get_htstamp(status, &htstamp);
>> +    now1 = pa_timespec_load(&htstamp);
>>       /* Hmm, if the timestamp is 0, then it wasn't set and we take
>> the current time */
>>       if (now1 <= 0)
>> diff --git a/src/modules/alsa/alsa-source.c
>> b/src/modules/alsa/alsa-source.c
>> index 94d4a09..17566e7 100644
>> --- a/src/modules/alsa/alsa-source.c
>> +++ b/src/modules/alsa/alsa-source.c
>> @@ -767,6 +767,7 @@ static void update_smoother(struct userdata *u) {
>>       int err;
>>       pa_usec_t now1 = 0, now2;
>>       snd_pcm_status_t *status;
>> +    snd_htimestamp_t htstamp = { 0, 0 };
>>       snd_pcm_status_alloca(&status);
>> @@ -775,18 +776,13 @@ static void update_smoother(struct userdata *u) {
>>       /* Let's update the time smoother */
>> -    if (PA_UNLIKELY((err = pa_alsa_safe_delay(u->pcm_handle, &delay,
>> u->hwbuf_size, &u->source->sample_spec, TRUE)) < 0)) {
>> +    if (PA_UNLIKELY((err = pa_alsa_safe_delay(u->pcm_handle, status,
>> &delay, u->hwbuf_size, &u->source->sample_spec, TRUE)) < 0)) {
>>           pa_log_warn("Failed to get delay: %s", pa_alsa_strerror(err));
>>           return;
>>       }
>> -    if (PA_UNLIKELY((err = snd_pcm_status(u->pcm_handle, status)) < 0))
>> -        pa_log_warn("Failed to get timestamp: %s",
>> pa_alsa_strerror(err));
>> -    else {
>> -        snd_htimestamp_t htstamp = { 0, 0 };
>> -        snd_pcm_status_get_htstamp(status, &htstamp);
>> -        now1 = pa_timespec_load(&htstamp);
>> -    }
>> +    snd_pcm_status_get_htstamp(status, &htstamp);
>> +    now1 = pa_timespec_load(&htstamp);
>>       /* Hmm, if the timestamp is 0, then it wasn't set and we take
>> the current time */
>>       if (now1 <= 0)
>> diff --git a/src/modules/alsa/alsa-util.c b/src/modules/alsa/alsa-util.c
>> index bb4e307..4a29a9a 100644
>> --- a/src/modules/alsa/alsa-util.c
>> +++ b/src/modules/alsa/alsa-util.c
>> @@ -1141,10 +1141,11 @@ snd_pcm_sframes_t pa_alsa_safe_avail(snd_pcm_t
>> *pcm, size_t hwbuf_size, const pa
>>       return n;
>>   }
>> -int pa_alsa_safe_delay(snd_pcm_t *pcm, snd_pcm_sframes_t *delay,
>> size_t hwbuf_size, const pa_sample_spec *ss, pa_bool_t capture) {
>> +int pa_alsa_safe_delay(snd_pcm_t *pcm, snd_pcm_status_t *status,
>> snd_pcm_sframes_t *delay, size_t hwbuf_size, const pa_sample_spec *ss,
>> +                       pa_bool_t capture) {
>>       ssize_t k;
>>       size_t abs_k;
>> -    int r;
>> +    int err;
>>       snd_pcm_sframes_t avail = 0;
>>       pa_assert(pcm);
>> @@ -1154,10 +1155,16 @@ int pa_alsa_safe_delay(snd_pcm_t *pcm,
>> snd_pcm_sframes_t *delay, size_t hwbuf_si
>>       /* Some ALSA driver expose weird bugs, let's inform the user about
>>        * what is going on. We're going to get both the avail and delay
>> values so
>> -     * that we can compare and check them for capture */
>> +     * that we can compare and check them for capture.
>> +     * This is done with snd_pcm_status() which provides
>> +     * avail, delay and timestamp values in a single kernel call to
>> improve
>> +     * timer-based scheduling */
>> -    if ((r = snd_pcm_avail_delay(pcm, &avail, delay)) < 0)
>> -        return r;
>> +    if ((err = snd_pcm_status(pcm, status)) < 0)
>> +        return err;
>> +
>> +    avail = snd_pcm_status_get_avail(status);
>> +    *delay = snd_pcm_status_get_delay(status);
>>       k = (ssize_t) *delay * (ssize_t) pa_frame_size(ss);
>> diff --git a/src/modules/alsa/alsa-util.h b/src/modules/alsa/alsa-util.h
>> index a4beed2..236a329 100644
>> --- a/src/modules/alsa/alsa-util.h
>> +++ b/src/modules/alsa/alsa-util.h
>> @@ -125,7 +125,7 @@ int pa_alsa_recover_from_poll(snd_pcm_t *pcm, int
>> revents);
>>   pa_rtpoll_item* pa_alsa_build_pollfd(snd_pcm_t *pcm, pa_rtpoll
>> *rtpoll);
>>   snd_pcm_sframes_t pa_alsa_safe_avail(snd_pcm_t *pcm, size_t
>> hwbuf_size, const pa_sample_spec *ss);
>> -int pa_alsa_safe_delay(snd_pcm_t *pcm, snd_pcm_sframes_t *delay,
>> size_t hwbuf_size, const pa_sample_spec *ss, pa_bool_t capture);
>> +int pa_alsa_safe_delay(snd_pcm_t *pcm, snd_pcm_status_t *status,
>> snd_pcm_sframes_t *delay, size_t hwbuf_size, const pa_sample_spec *ss,
>> pa_bool_t capture);
>>   int pa_alsa_safe_mmap_begin(snd_pcm_t *pcm, const
>> snd_pcm_channel_area_t **areas, snd_pcm_uframes_t *offset,
>> snd_pcm_uframes_t *frames, size_t hwbuf_size, const pa_sample_spec *ss);
>>   char *pa_alsa_get_driver_name(int card);
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