Re: Sending UDP data at a fixed rate

From:

"Mark Salsbery [MVP]" <MarkSalsbery[MVP]@newsgroup.nospam>

Newsgroups:

microsoft.public.vc.language

Date:

Fri, 29 Feb 2008 14:48:31 -0800

Message-ID:

<BDB0DC79-5559-41E2-B038-7D1DF48FA676@microsoft.com>

I'm curious....how are you measuring the inter-datagram delay? Is there
ever a chance sendto() is blocking?

In my multimedia communication software, I get very steady inter-datagram
timing on XP and Vista, but on 2000 it gets chunky (datagrams sent in
bunches).
This drove me nuts for a while trying to implement jitter buffers for
multimedia streaming :)

Mark

--
Mark Salsbery
Microsoft MVP - Visual C++

"PaulH" <paul.heil@gmail.com> wrote in message
news:44696dd8-0b37-4fe2-9884-abb7a9134e0e@p73g2000hsd.googlegroups.com...

On Feb 29, 2:22 pm, "Mark Salsbery [MVP]"
<MarkSalsbery[MVP]@newsgroup.nospam> wrote:

"PaulH" <paul.h...@gmail.com> wrote in message

news:e6f36848-5086-4e6a-9933-902a307b418c@i12g2000prf.googlegroups.com...

I have a program that I want to use to send UDP data frames at a fixed
rate. Right now, at 25ms between frames about 1 in 10 is delayed by a
few ms. I've used other programs that manage to get this kind of
success at 10ms between frames.

I'm using a multimedia timer (see below) to get my current level of
accuracy. What can I do to improve things?

Thanks,
PaulH

int delay = 25; //25 ms between frames
HANDLE hSendNextFrame = CreateEvent( NULL, FALSE, FALSE, NULL );

Do you call timeBeginPeriod() before creating the periodic timer?

Something like:

TIMECAPS tc;
if (::timeGetDevCaps(&tc, sizeof(TIMECAPS)) == TIMERR_NOERROR)
{
// Try for 1ms resolution - accept best
UINT TimerRes = min(max(tc.wPeriodMin, 1), tc.wPeriodMax);
::timeBeginPeriod(TimerRes);

Mark

--
Mark Salsbery
Microsoft MVP - Visual C++

MMRESULT mmNextFrameTimer = timeSetEvent( delay,
1,
reinterpret_cast<
LPTIMECALLBACK >( hSendNextFrame ),
NULL,
TIME_PERIODIC |
TIME_CALLBACK_EVENT_SET );

while( TRUE ) {
if( sendto( address, data ) < 0 ) {
//error condition
}

::WaitForSingleObject( hSendNextFrame, delay + 100 );
}

timeKillEvent( mmNextFrameTime );
CloseHandle( hSendNextFrame );

Good thought. But, timeSetEvent() already calls timeBeginPeriod() to
set the accuracy.
http://blogs.msdn.com/larryosterman/archive/2005/09/08/462477.aspx

I tried it anyway to see if it helped. It did not.

-PaulH