serial_port.h

#ifndef _SERIAL_PORT_H_
#define _SERIAL_PORT_H_


#ifdef _USE_WIN_API_

#include <windows.h>

#define SerialDeviceHandle HANDLE
#define DEFAULT_SERIAL_DEVICE_NAME "COM1"
#define INVALID_HANDLE  INVALID_HANDLE_VALUE

// https://www.xanthium.in/Serial-Port-Programming-using-Win32-API

static inline SerialDeviceHandle serialDeviceOpen(char* deviceName) {
    SerialDeviceHandle h;

    h = CreateFile(
        deviceName,                  //port name
        GENERIC_READ | GENERIC_WRITE, //Read/Write
        0,                            // No Sharing
        NULL,                         // No Security
        OPEN_EXISTING,// Open existing port only
        0,            // Non Overlapped I/O
        NULL);        // Null for Comm Devices

    if (h != INVALID_HANDLE) {
        BOOL result;
        COMMTIMEOUTS timeouts = { 0 };

        DCB dcbSerialParams = { 0 }; // Initializing DCB structure
        dcbSerialParams.DCBlength = sizeof(dcbSerialParams);
    
        result = GetCommState(h, &dcbSerialParams);

        if (!result) {
            return INVALID_HANDLE;
        }

        dcbSerialParams.BaudRate = CBR_38400;  // Setting BaudRate = 38400
        dcbSerialParams.ByteSize = 8;         // Setting ByteSize = 8
        dcbSerialParams.StopBits = ONESTOPBIT;// Setting StopBits = 1
        dcbSerialParams.Parity   = NOPARITY;  // Setting Parity = None

        result = SetCommState(h, &dcbSerialParams);
        if (!result) {
            return INVALID_HANDLE;
        }

        timeouts.ReadIntervalTimeout         = 50; // in milliseconds
        timeouts.ReadTotalTimeoutConstant    = 50; // in milliseconds
        timeouts.ReadTotalTimeoutMultiplier  = 10; // in milliseconds
        timeouts.WriteTotalTimeoutConstant   = 50; // in milliseconds
        timeouts.WriteTotalTimeoutMultiplier = 10; // in milliseconds

        result = SetCommTimeouts(h, &timeouts);
        if (!result) {
            return INVALID_HANDLE;
        }

        return h;
    } else {
        return INVALID_HANDLE;
    }
  
}

void serialDeviceCheckName(char* name, int maxSize) {
    int nameLen = strlen(name);
    //convert comxx to COMxx
    if (strncmp(name, "com", 3) == 0 && (nameLen > 3 && name[3] >= '0' && name[3] <= '9')) {
        name[0] = 'C';
        name[1] = 'O';
        name[2] = 'M';
    }

    // convert COMxx and higher to \\\\.\\COMxx
    if (strncmp(name, "COM", 3) == 0 && (nameLen > 4 && name[3] >= '0' && name[3] <= '9')) {
        if (nameLen + 4 < maxSize) {
            int i;
            for (i = nameLen - 1; i >= 0; i--) {
                name[ i + 4] = name[i]; 
            }
            name[0] = '\\';
            name[1] = '\\';
            name[2] = '.';
            name[3] = '\\';
        }
    }
}

static inline void serialDeviceClose(SerialDeviceHandle deviceHandle) {
    CloseHandle(deviceHandle);
}

static inline int serialDeviceWrite(SerialDeviceHandle deviceHandle, char* buffer, int bytesToWrite) {
    DWORD written = 0;
    WriteFile(deviceHandle, buffer, bytesToWrite, &written, NULL);
    return (int) written;
}

static inline int serialDeviceRead(SerialDeviceHandle deviceHandle, char* buffer, int bytesToRead) {
    DWORD read = 0;
    ReadFile(deviceHandle, buffer, bytesToRead, &read, NULL);
    return (int) read;
}

#else

#include <ctype.h>
#include <fcntl.h>
#include <errno.h>

#include <termios.h>

#define SerialDeviceHandle int
#define DEFAULT_SERIAL_DEVICE_NAME "/dev/ttyUSB0"

#define INVALID_HANDLE -1

static inline SerialDeviceHandle serialDeviceOpen(char* deviceName) {

    SerialDeviceHandle h;
    h = open(deviceName, O_RDWR | O_NOCTTY  | O_NONBLOCK);

    if (h != INVALID_HANDLE) {
        //set the serial port parameters
        struct termios serial;

        memset(&serial, 0, sizeof(struct termios));
        cfsetispeed(&serial, B38400);
        cfsetospeed(&serial, B38400);

        serial.c_cflag |= CS8; // no parity, 1 stop bit
        serial.c_cflag |= CREAD | CLOCAL;

        if (0 != tcsetattr(h, TCSANOW, &serial)) {
            close(h);
            printf("Error: failed to set serial parameters %i, %s\n", errno, strerror(errno));
            return INVALID_HANDLE;
        }

        //ensure no leftover bytes exist on the serial line
        tcdrain(h);
        tcflush(h, TCIOFLUSH); //flush both queues
        return h;
    } else {
        return INVALID_HANDLE;
    }
}

void serialDeviceCheckName(char* name, int maxSize) {
    //nothing to check    
}

static inline void serialDeviceClose(SerialDeviceHandle deviceHandle) {
    close(deviceHandle);
}

static inline int serialDeviceWrite(SerialDeviceHandle deviceHandle, char* buffer, int bytesToWrite) {
    return write(deviceHandle, buffer, bytesToWrite);
}

static inline int serialDeviceRead(SerialDeviceHandle deviceHandle, char* buffer, int bytesToRead) {
    return read(deviceHandle, buffer, bytesToRead);
}
#endif

#endif /* _SERIAL_PORT_H_ */