Re: Multimedia Timer
On Feb 11, 10:33 pm, malachy.mo...@gmail.com wrote:
On Feb 11, 11:46 am, clinisbut <clinis...@gmail.com> wrote:
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.
<< snip >>
Does the recipient of the serial port data need to receive one "chunk"
of data every 20 ms, without fail? In other words, is it a
requirement that your program send exactly one single "chunk" of
serial port data at each and every single interval of 20 ms?
If so, then you probably need to re-think your design and your use of
the Windows OS, while repeating the mantra "Windows is not a RTOS,
Windows is not a RTOS ...."
In fairness, you might be using WinCE, which in fact _is_ a RTOS, but
somehow your post leads me to believe otherwise.
Malachy
Maybe I should post some code to find the "bottleneck".
1- Timer_SendData just calls a function Send_UART()
2- Send_UART does a pMySerial_UIThread->PostThreadMessage( WRITE,
buffer, 0 );
3- WRITE handler message sends through serial port:
unsigned char* buffer = (unsigned char*)wParam;
BOOL ok = ::WriteFile( hComm, buffer, lParam, &bytesWritten,
&ovWriter );
if( !ok )
{
DWORD err = ::GetLastError();
if( err!=ERROR_IO_PENDING ) //Error grave
{
PostQuitMessage(0);
return;
}
HANDLE waiters[2];
waiters[0] = ShutdownEvent;
waiters[1] = WriteEvent;
DWORD razon = ::WaitForMultipleObjects( 2, waiters, FALSE,
INFINITE );
switch( razon )
{
case WAIT_OBJECT_0:
err = ::GetLastError();
delete buffer;
PostQuitMessage(0);
return;
case WAIT_OBJECT_0 + 1:
ok = ::GetOverlappedResult( hComm, &ovWriter, &bytesWritten,
TRUE );
if( !ok )
{ PostQuitMessage(0);
return;
}
break;
default:
PostQuitMessage(0);
return;
}
}
delete buffer;
And answering some questions:
Are you sure that your operation is not taking longer than 20ms?
MMm not really sure...
Are you pausing the timer during your operation?
Nop, should I?
Does the recipient of the serial port data need to receive one "chunk"
of data every 20 ms, without fail? In other words, is it a
requirement that your program send exactly one single "chunk" of
serial port data at each and every single interval of 20 ms?
Not exactly, look:
The device is recollecting data and storing it into a buffer.
To request this data, my app sends a frame to the device.
If my app takes too long to send this request, I can lose data because
the device can overwrite data not requested if the buffer gets full.
That's because I need those 20ms delay between two requests.