time coversions and effect of time drift.

[Ram]

Hi,
I am looking for functions in 'C' to convert the struct timeval
into double,
add milliseconds to struct timeval.

Does anybody know how to do it.
What is the effect of "time drift" in time in linux. How can this be
taken care of ?.

Scenario ( )
{
StartTime = gettimeofday ( ) ;
PlayTime = StartTime + 2millseconds ;

while (1) {
Do Some Work ;

Now = gettimeofday ( ) ;

If (Now == PlayTime)
Play ( ) ;

PlayTime = Now + 2milliseconds ;
}

}

I Think Now and PlayTime will never be equal. I call this drift.
How does one take care ?.

Please Advice.

Any Pointers ?

Regards,
Ram

[Thad Smith]

Ram wrote:

Scenario ( )
{
StartTime = gettimeofday ( ) ;
PlayTime = StartTime + 2millseconds ;

while (1) {
Do Some Work ;

Now = gettimeofday ( ) ;

If (Now == PlayTime)
Play ( ) ;

PlayTime = Now + 2milliseconds ;
}

}

I Think Now and PlayTime will never be equal. I call this drift.

if (Now >= PlayTime)

assuming that Now and PlayTime don't overflow.

You can somewhat similar logic using fixed point timers that explicitly
do overflow:
unsigned int dif = PlayTime - Now;
if (dif > -MAX_LATENCY) {
play();
PlayTime += PLAY_INTERVAL;
}

--
Thad