baudrate serial windows port

Question

To probe the windows serial port I have written this program. I set the serial port baudrate to 115200 bps. When I run this program the elapsed time is 1250 ms, so that, the baudrate only reachs 102400 bps. I also check in reception the baudrate with a similar program and the baudrate is the same.

Here is the program:

char* message = 
"xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx";

int numBytes = 144;

c0 = clock()

for (;;)

{

sendSerial(&hCom, message, numBytes );
tx +=numBytes;

//14400 bytes * 8 = 115200 bps

    if (tx >= 14400)
    {
        c1 = clock();
        runtime_diff_ms = (c1 - c0) * 1000. / CLOCKS_PER_SEC;
        printf("Tx frames %d Time ms %f", tx, runtime_diff_ms);
        system ("pause");
        return -1;
    }
}

bool sendSerial(HANDLE *hCom, char *WriteBuffer, DWORD dwBytesToWrite)
{
    DWORD dwBytesWritten = 0;
    BOOL bErrorFlag = FALSE;

     bErrorFlag = WriteFile( 
                    *hCom,           // open file handle
                    WriteBuffer,      // start of data to write
                    dwBytesToWrite,  // number of bytes to write
                    &dwBytesWritten, // number of bytes that were written
                    NULL);    
...
}

These are my serial port specifications:

DCB dcbSerialParams;
COMMTIMEOUTS timeouts;  
dcbSerialParams.BaudRate=CBR_115200;
dcbSerialParams.ByteSize=8;
dcbSerialParams.StopBits=ONESTOPBIT;
dcbSerialParams.Parity=NOPARITY;

timeouts.ReadIntervalTimeout=MAXDWORD; 
timeouts.ReadTotalTimeoutMultiplier=MAXDWORD; 
timeouts.ReadTotalTimeoutConstant=5000; // 5sec
timeouts.WriteTotalTimeoutMultiplier=10;
timeouts.WriteTotalTimeoutConstant=100;

Anyone know how to fix this problem to reach 115200 bps?

Answer 1

There are 10 bits per character - 8 bits for the data plus a start and stop bit.

If you calculate how long 14400 characters at 10 bits per character should take at 115200 bps then you get 1250 ms:

(14400 characters * 10 bits/character) / (115200 bits/second) =  1.250 seconds