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added: reduce output timing jitter by setting the display thread to SCHED_FIFO, and by passing the timestamps through a low pass filter

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This commit is contained in:
Bob van Loosen 2013-03-26 23:39:26 +01:00
parent b7f56dfe4d
commit 11b5eeb827
1 changed files with 37 additions and 1 deletions
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38
src/bitvis/bitvis.cpp
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@ -284,6 +284,27 @@ void CBitVis::Run()
void CBitVis::Process()
{
//set priority to SCHED_FIFO to improve timing
int policy;
sched_param param;
int returnv = pthread_getschedparam(m_thread, &policy, &param);
if (returnv == 0)
{
policy = SCHED_FIFO;
param.sched_priority = sched_get_priority_min(SCHED_FIFO);
returnv = pthread_setschedparam(m_thread, policy, &param);
if (returnv == 0)
Log("successfully set thread priority of transmit thread to SCHED_FIFO");
else
LogError("pthread_setschedparam: %s", strerror(returnv));
}
else
{
LogError("pthread_getschedparam: %s", strerror(returnv));
}
int64_t smoothtime = 0;
CLock lock(m_condition);
while (!m_stop)
{
@ -297,8 +318,20 @@ void CBitVis::Process()
CTcpData data = m_data.front().second;
m_data.pop_front();
if (smoothtime == 0)
{
//init smoothtime first with a timestamp
smoothtime = time;
}
else
{
//filter out timing jitter
smoothtime += 1000000 / m_fps;
smoothtime += (time - smoothtime) / 100;
}
lock.Leave();
USleep(time - GetTimeUs());
USleep(smoothtime - GetTimeUs());
lock.Enter();
if (m_socket.IsOpen() && m_socket.Write(data) != SUCCESS)
@ -522,6 +555,9 @@ void CBitVis::SendData(int64_t time)
memset(end, 0, sizeof(end));
data.SetData(end, sizeof(end), true);
//add 10 milliseconds to the timestamp, since the current timestamp
//might already have passed because of processing, this decreases
//jitter in the display output
CLock lock(m_condition);
m_data.push_back(make_pair(time + 10000, data));
lock.Leave();