On 02/15/2018 10:22 AM, Georg Chini wrote:
> On 14.02.2018 23:09, Raman Shishniou wrote:
>> On 02/15/2018 12:03 AM, Georg Chini wrote:
>>> The null-source currently reports the negative of the correct latency.
>>> Also the memchunk passed to pa_source_post() is not initialized with
>>> silence.
>>>
>>> This patch fixes both issues.
>>> ---
>>> src/modules/module-null-source.c | 5 +++--
>>> 1 file changed, 3 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/src/modules/module-null-source.c b/src/modules/module-null-source.c
>>> index 41f17bd9..6310bda9 100644
>>> --- a/src/modules/module-null-source.c
>>> +++ b/src/modules/module-null-source.c
>>> @@ -100,7 +100,7 @@ static int source_process_msg(pa_msgobject *o, int code, void *data, int64_t off
>>> pa_usec_t now;
>>> now = pa_rtclock_now();
>>> - *((int64_t*) data) = (int64_t)u->timestamp - (int64_t)now;
>>> + *((int64_t*) data) = (int64_t)now - (int64_t)u->timestamp;
>>> return 0;
>>> }
>>> @@ -142,8 +142,9 @@ static void thread_func(void *userdata) {
>>> if ((chunk.length = pa_usec_to_bytes(now - u->timestamp, &u->source->sample_spec)) > 0) {
>>> - chunk.memblock = pa_memblock_new(u->core->mempool, (size_t) -1); /* or chunk.length? */
>>> + chunk.memblock = pa_memblock_new(u->core->mempool, chunk.length);
>>> chunk.index = 0;
>>> + pa_silence_memchunk(&chunk, &u->source->sample_spec);
>>> pa_source_post(u->source, &chunk);
>>> pa_memblock_unref(chunk.memblock);
>> I think you need to change the next line too:
>> - u->timestamp = now;
>> + u->timestamp += pa_bytes_to_usec(chunk.length, &u->source->sample_spec);
>> }
>>
>> to make silence generator more stable
>>
>>
> How would that make it more stable? It will only lower the precision of the time stamp.
Nope. It will increase the precision. Actually null-source send pa_bytes_to_usec(chunk.length)
microseconds of data each iteration which can be smaller than (now - u->timestamp).
It must increase timestamp by actually data sent. Accumulated difference will be corrected
on the next iteration by sending more data.
For example each 10ms we need to send a 99.5 bytes of data (s8, mono, 9950Hz),
i.e. pa_usec_to_bytes() does: bytes = usecs * 0.00995
and pa_bytes_to_usec() does: usecs = bytes / 0.00995
First iteration:
u->timestamp == 0
now = pa_rtclock_now() == 10ms == 10000us
bytes = pa_usec_to_bytes(10000 - 0) = 99
... send 99 bytes of data ...
u->timestamp += pa_bytes_to_usec(99) == 9949
Second iteration:
u->timestamp == 9949
now = pa_rtclock_now() == 20ms == 20000us
bytes = pa_usec_to_bytes(20000 - 9949) = 100
... send 100 bytes of data ...
u->timestamp += pa_bytes_to_used(100) = 9949 + 10050 = 19999
Third iteration:
u->timestamp == 19999
now = pa_rtclock_now() == 30ms == 30000us
bytes = pa_usec_to_bytes(30000 - 19999) = 99
... send 99 bytes of data ...
u->timestamp += pa_bytes_to_used(99) = 19999 + 9949 = 29948
and so on
Current implementation will send only 99 bytes of data each iteration.
--
Raman
