Trouble sending MIDI data over serial/COM port in C - c

Question

I am writing a C program in Visual Studio 2013 to send MIDI data to a MIDI device over a serial (COM) port. My code thus far is as follows:
Opening the serial/COM port:
unsigned int SERIALCOMMS_OpenPort(HANDLE *hSerialPort,
unsigned int comPortNum,
unsigned int baudRate)
{
DCB dcbSerialParams = {0};
COMMTIMEOUTS timeouts = {0};
unsigned char portStr[COM_PORT_LEN_MAX];
/* Initialisations */
memset(portStr, 0x00, sizeof(portStr));
/* Construct the COM port string */
sprintf(portStr, "%sCOM%d", COM_PORT_PREFIX, comPortNum);
printf("Opening serial port...");
*hSerialPort = CreateFile((LPCSTR)portStr,
(GENERIC_READ | GENERIC_WRITE),
0,
NULL,
OPEN_EXISTING,
FILE_ATTRIBUTE_NORMAL,
NULL);
if (*hSerialPort == INVALID_HANDLE_VALUE)
{
if (GetLastError() == ERROR_FILE_NOT_FOUND)
{
printf("\nError: \nThe system cannot find the file specified (%s)\n", portStr);
return 1;
}
else if (GetLastError() == ERROR_INVALID_NAME)
{
printf("\nError: \n%s port name syntax is incorrect'\n", portStr);
return 1;
}
else
{
printf("\nHandle creation error code: %x\n", GetLastError());
return 1;
}
puts("\t...CreateFile returned an invalid handle value");
}
printf("OK\n");
/* Set device parameters */
dcbSerialParams.DCBlength = sizeof(dcbSerialParams);
if (GetCommState(*hSerialPort, &dcbSerialParams) == 0)
{
printf("Error getting device state\n");
CloseHandle(*hSerialPort);
return 1;
}
dcbSerialParams.BaudRate = baudRate;
dcbSerialParams.ByteSize = 8;
dcbSerialParams.StopBits = ONESTOPBIT;
dcbSerialParams.Parity = NOPARITY;
if (SetCommState(*hSerialPort, &dcbSerialParams) == 0)
{
printf("Error setting device parameters\n");
return 1;
}
/* Set COM port timeout settings */
timeouts.ReadIntervalTimeout = 50;
timeouts.ReadTotalTimeoutConstant = 50;
timeouts.ReadTotalTimeoutMultiplier = 10;
timeouts.WriteTotalTimeoutConstant = 50;
timeouts.WriteTotalTimeoutMultiplier = 10;
if (SetCommTimeouts(*hSerialPort, &timeouts) == 0)
{
printf("Error setting timeouts\n");
return 1;
}
return 0;
}
The constant COM_PORT_PREFIX is defined as follows:
#define COM_PORT_PREFIX "\\\\\.\\"
The port opens fine. However, when I send data to it, it seems that the received data is much different than what is supposed to be sent. I am testing this with an Arduino that is programmed to spool out the received data as integer/hex values, for purposes of testing what is actually being sent by the PC.
Here is the code of the function used to send the data:
unsigned int SERIALCOMMS_Send(HANDLE hSerialPort,
unsigned char *txData,
unsigned int *byteCount)
{
unsigned int bytesWritten = 0u;
/* Transmit data */
if (!WriteFile(hSerialPort, txData, *byteCount, &bytesWritten, NULL))
{
printf("Error transmitting data\n");
return 1;
}
printf("\n%d bytes written\n", bytesWritten);
return 0;
}
Using the following method with the above "Send" function:
unsigned int byteCount = 1u;
unsigned char dataByte[1];
SERIALCOMMS_Send(hSerialPort, dataByte, &byteCount);
When I send the following MIDI data (hex values), it gets received as follows:
0x91 gets received as 0xC9
0x92 gets received as 0xC8
0x93 gets received as 0xC9
0x94 gets received as 0xCA
0x95 gets received as 0xCB
0x24 gets received as 0xD2
Clearly, nothing of this makes sense. I am unable to figure out what is causing this. Some of the project properties in Visual Studio are configured as follows:
Project settings
One possible aspect might be the specified character set (currently set as "Use Multi-Byte Character Set"). If I change this to "Use Unicode Character Set", then the program is unable to connect with the COM port.
Thinking logically of the problem, it must have to do with the way I am sending the data. I am most probably passing the MIDI data to be sent in the wrong manner, but I honestly cannot figure out what is causing the problem and what I am doing wrong.
Any help will be greatly appreciated.
UPDATE:
The baud rate is set at 31250 bps (as per MIDI standard) on both the PC and the Arduino.

Answer 1

It seems that according to this answer on another thread on stackoverflow it is not that simple to just use non-standard baud rates on the Windows platform due to the crystal oscillation frequency used in PCs for calculating the UART baud rates and the way the baud rates are derived therefrom. Thus it seems that it is best to stick to standard baud rates.
Using a standard baud rate solved my problem. However, it thus enforces a change in the specifications on the hardware used in my case, which is not ideal.
This, of course, raises the following question - what does one have to do to be able to use non-standard baud rates? Would one have to write an additional/custom driver for that?