Simple Serial Communication Utilities

• Download SerialExample - 602.1 KB
• Download rs232 - 3.9 KB
• Download lisports - 6.4 KB

Introduction

In embedded designing, it is very common to need a communication channel with a PC. The simplest way is the serial communication because every microcontroller has UART ports to make serial communication with the world. But on the computer, it's not always that easy.

Here, I present a very simple serial communnication library, with non blocking reading and no-event-dependant which can be an advantage denpending on the type of software we need.

Along with this, I provide a serial port enumerator, which is very useful, and a simple Timer class which will allow us to measure intervals and automate some actions. This timer class is not event-driven so you have to poll the state of the interval to know if it's time to do something.

In future articles, I will explain how to use event-driven timers to really automate a function. But for now, this simple timer is enough for our aplication.

Using the Code

In the code, I use three separate libraries. One for the serial communication, one for the timing and one for the summary of the available comports in the PC. I upload each library separately and an example project using them.

RS232 Library

This library brings a simple and easy to use interface with the COM ports of the PC. The header presents these functions:

#ifndef rs232_INCLUDED
#define rs232_INCLUDED

#ifdef __cplusplus
extern "C" {
#endif

#include <stdio.h>
#include <string.h>


#ifdef __linux__

#include <termios.h>
#include <sys/ioctl.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <limits.h>

#else

#include <windows.h>

#endif

int RS232_OpenComport(int, int);
int RS232_PollComport(int, unsigned char *, int);
int RS232_SendByte(int, unsigned char);
int RS232_SendBuf(int, unsigned char *, int);
void RS232_CloseComport(int);
void RS232_cputs(int, const char *);
int RS232_IsDCDEnabled(int);
int RS232_IsCTSEnabled(int);
int RS232_IsDSREnabled(int);
void RS232_enableDTR(int);
void RS232_disableDTR(int);
void RS232_enableRTS(int);
void RS232_disableRTS(int);

#ifdef __cplusplus
} /* extern "C" */
#endif

#endif

This library was writen by Teunis van Beelen, more information here.

Com Ports Enumerator

This library brings a simple method for enumerating the available serial ports in the PC. It isn't perfect but it works fine.

#ifndef LISTPORTS_H
#define LISTPORTS_H

#define VERSION_LISTPORTS 0x00020000

#ifdef __cplusplus
extern "C"{
#endif

#include <windows.h>

typedef struct
{
  LPCTSTR lpPortName;     /* "COM1", etc. */
  LPCTSTR lpFriendlyName; /* Suitable to describe the port, as for  */
                          /* instance "Infrared serial port (COM4)" */
  LPCTSTR lpTechnology;   /* "BIOS","INFRARED","USB", etc.          */
}LISTPORTS_PORTINFO;

typedef BOOL (CALLBACK* LISTPORTS_CALLBACK)(LPVOID              lpCallbackValue,
                                            LISTPORTS_PORTINFO* lpPortInfo);
/* User provided callback funtion that receives the information on each
 * serial port available.
 * The strings provided on the LISTPORTS_INFO are not to be referenced after
 * the callback returns; instead make copies of them for later use.
 * If the callback returns FALSE, port enumeration is aborted.
 */

BOOL ListPorts(LISTPORTS_CALLBACK lpCallback,LPVOID lpCallbackValue);
/* Lists serial ports available on the system, passing the information on
 * each port on succesive calls to lpCallback.
 * lpCallbackValue, treated opaquely by ListPorts(), is intended to carry
 * information internal to the callback routine.
 * Returns TRUE if succesful, otherwise error code can be retrieved via
 * GetLastError().
 */

#ifdef __cplusplus
}
#endif

#elif VERSION_LISTPORTS!=0x00020000
#error You have included two LISTPORTS.H with different version numbers
#endif

typedef BOOL (CALLBACK* LISTPORTS_CALLBACK)(LPVOID              lpCallbackValue,
                                            LISTPORTS_PORTINFO* lpPortInfo);

string comPorts[4]; // Vector containing available ports
int port_cnt=0;

/* Callback function that list the available ports */
static BOOL CALLBACK callback(LPVOID lpCallbackValue,LISTPORTS_PORTINFO* lpPortInfo)
{
  _tprintf(
    TEXT("\"%s\" \"%s\" \"%s\"\n"),
    lpPortInfo->lpPortName,lpPortInfo->lpTechnology,lpPortInfo->lpFriendlyName);
    comPorts[port_cnt] = lpPortInfo->lpPortName;
    port_cnt++;
  return TRUE;
}

#include <iostream>
#include "rs232.h"
#include "timerclass.h"
#include "listports.h"
#include <tchar.h>

using namespace std;

string comPorts[4]; // Vector containing available ports
int port_cnt=0;

/* Definition of the Callback function that list the available ports */
static BOOL CALLBACK callback(LPVOID lpCallbackValue,LISTPORTS_PORTINFO* lpPortInfo)
{
  _tprintf(
    TEXT("\"%s\" \"%s\" \"%s\"\n"),
    lpPortInfo->lpPortName,lpPortInfo->lpTechnology,lpPortInfo->lpFriendlyName);
    comPorts[port_cnt] = lpPortInfo->lpPortName;
    port_cnt++;
  return TRUE;
}

int main(int argc, char* argv[])
{

    int n;
    unsigned char buf[4096];
    int cport_nr = 4;
    int bdrate = 9600;

    //unsigned char outBuffer[128];
    string outBuffer;

    ListPorts(callback,NULL); //Calling to the list ports function

    cout << "Available ports: " << endl;
    for(int i=0; i<port_cnt; i++)
    {
        cout << (i+1) << ": " << comPorts[i] << endl;
    }
    cout << endl << "Choose a port ";
    cin >> cport_nr;
    cport_nr--; // according to rs232.h, the port numbers start on 0 for COM1

    if(RS232_OpenComport(cport_nr, bdrate)) //Open the port
    {
        cout << "Can not open com port " << comPorts[cport_nr];

        return(0);
    }

    while(1)
  {
    //n = RS232_PollComport(cport_nr, buf, 4095);
    cout << "Type message to send" << endl << "Type 'quit' to exit" << endl;
    cin >> outBuffer;

    if(outBuffer == "quit")
    {
        RS232_CloseComport(cport_nr);
        return 0;
    }

    RS232_SendBuf(cport_nr, (unsigned char*) outBuffer.c_str(), outBuffer.size());

    Sleep(100);
    n = RS232_PollComport(cport_nr, buf, 4096);
    if(n>0)
    {
        buf[n]=0;
        cout << "Received: " << buf << endl << endl;
    }
    buf[0]=0;

  }
}

RS232_SendBuf(cport_nr, (unsigned char*) outBuffer.c_str(), outBuffer.size());

n = RS232_PollComport(cport_nr, buf, 4096);

if(n>0)
    {
        buf[n]=0;
        cout << "Received: " << buf << endl << endl;
    }