Multimedia Timer

From:

clinisbut <clinisbut@gmail.com>

Newsgroups:

microsoft.public.vc.mfc

Date:

Mon, 11 Feb 2008 08:46:51 -0800 (PST)

Message-ID:

<ac5877e2-3c6d-4c4e-9d05-8b9a58de16c6@e4g2000hsg.googlegroups.com>

I need to execute some code every 20ms. This code is just send some
data through serial port, so I think it's not heavy.

At first I was using SetTimer function and OnTimer event, but with no
good results: seems that not sending every 20ms, instead is sending 3
or so consecutive frames at same time.

Today I tried the multimedia timers, and seems that does the same.
Inside my TimeEventHandler, I trace:

          TRACE( "Time:%d\n", GetTickCount() );

And I see that sometimes event handler fires up more than one time at
same time, look:

Time:30664983
Time:30664983
Time:30664983
Time:30664993
Time:30665013
Time:30665033
Time:30665054
Time:30665074

I'm measuring correctly the time elapsed between calls?
This is the code to create a multimedia timer I'm using:

void CMyAppDlg::SomeFunctio()
{
       TIMECAPS tc;
       timeGetDevCaps( &tc, sizeof(TIMECAPS) );
       DWORD resolution = min( max( tc.wPeriodMin, 0 ),
tc.wPeriodMax );
       timeBeginPeriod( resolution );

       m_Timer = timeSetEvent( TIME_ELAPSE, resolution, StartTimer,
DWORD(this), TIME_PERIODIC );
}

void CALLBACK CMyAppDlgDlg::StartTimer( UINT wTimerID, UINT msg, DWORD
dwUser, DWORD dw1, DWORD dw2 )
{
    CMyAppDlg* obj = (CMyAppDlgDlg*) dwUser;
    obj->Timer_SendData( wTimerID );

}

void CMyAppDlg::Timer_SendData( UINT nIDEvent )
{
      TRACE( "Time:%d\n", GetTickCount() );
}

The TIMECAPS.wPeriodMin on my system is '1', so I don't think that's
the problem...