Re: interthread communication

From:

mfc <mfcprog@googlemail.com>

Newsgroups:

microsoft.public.vc.mfc

Date:

Sat, 21 Aug 2010 01:26:20 -0700 (PDT)

Message-ID:

<8821ceb1-b914-48e6-9810-68fbd01ff82d@5g2000yqz.googlegroups.com>

thanks for your response. I think I understand now the part creating
the buffer for the serial port writer.

void CEthSoc::RxData(DATA *ptr, uint size)
{
     CByteArray *pData = new CByteArray;

    pData->SetSize(sizeof(size));
    memcpy(pData->GetData(), &ptr->Data[0], sizeof(size));

    //send data to specific serial port
   ::PostThreadMessage(m_ThreadIDs[ptr->Universe], UWM_SEND_DMX_DATA,
(WPARAM)pData, size);
}

void CSerialWrite::OnSendData(WPARAM wParam, LPARAM lParam)
{
    DWORD bytesWritten, EventDWord, RxBytes, TxBytes;
    ULONG status;
    BOOL waiting = TRUE;

    CByteArray * data = (CByteArray *)wParam;
    ASSERT(data != NULL);
    if(data == NULL)
       return; //

   while(running)
   {
         //write data to the serial port
         FT_Write(ftHandle, data->GetData(), 1, &bytesWritten);

        //waiting for CTS = high
      while(waiting)
      {
            //wait until the packet has been sent by the serial port
           WaitForSingleObject(hEvent,INFINITE);

            FT_GetStatus(ftHandle,&RxBytes,&TxBytes,&EventDWord);
           if (EventDWord & FT_EVENT_MODEM_STATUS)
           {
      FT_GetModemStatus(ftHandle, &status);
     if (status & 0x00000010)
      { // CTS is high
        waiting = FALSE;
     }
         }
     }

     //-> ready to get the new data pkt

    if(no_new_data_pkt) -> tx the last buffer again

     else
    {
         //delete buffer
        delete [] data;

        //tx new buffer
    }
  } //end of running while()

  //-> stop tx data to serial port
}

The problem: If the first ethernet packet will arrive it will be send
by a pointer to the CByteArray to this function. Now the serial port
writer has to write a continuous data-stream as long as the running
condition is true. That means, if a new ethernet packet will arrive,
then transmit this new packet; if there`s no new ethernet packet, then
transmit the old buffer again (for a specific time). This is the
algorithm to acchieve.

If there`s another PostThreadMessage(UWM_SEND_DMX_DATA) while sending
the last packet to the serial port - how is it possible to get this
message (CSerialWrite::OnSendData)? Immediately after returning the
OnSendData() function (do not using the running condition)? If that`s
right - how is it then possible to start the OnSendData() function
again, if there`s no new ethernet packet received??? Because if
there`s no new ethernet packet, the serial port has to transmit the
last ethernet packet again.

I hope you understand the algorithm.

best regards
Hans