serial port to poll on request

This is a discussion on serial port to poll on request within the C++ Programming forums, part of the General Programming Boards category; I currently have two programs("reading" and "writing") and each program run on one PC to do textfile transferring/logging. The PCs ...

  1. #1
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    Jun 2009
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    serial port to poll on request

    I currently have two programs("reading" and "writing") and each program run on one PC to do textfile transferring/logging. The PCs is connected via a null modem cable. The program is running in windows and is a DOS application written in c++. The programs work but it is working in a way that i have to run the "reading" program first to let it poll before i can run the "writing" program to send the content of the text file.

    How do i make it in a way that the "reading" program will only start polling upon request from the "writing" program? Meaning, when i clicked the "writing" program to send the data, it will communicate with the "reading" program to start and get ready to receive.


    This is my codes for the "reading" side (Upon receiving the content from the "writing" side, it will log it into a text file called "new.txt")
    Code:
    #include "windows.h"
    #include <stdio.h>
    #include <ctype.h>
    #include <io.h>
    #include <conio.h>
    #include <stdlib.h>
    
    #define maxBytes 111
    
    int main()
    {
    	HANDLE hSerial;
    	DCB dcbSerialParams = {0};
    	COMMTIMEOUTS timeouts = {0};
    	DWORD dwBytesRead = 0;
    	char szBuff[maxBytes] = {0};
    	int firstdigit = 0;
    	FILE *fp;
    	int i;
    
    	//opening the serial port
    	hSerial = CreateFile("COM1", GENERIC_READ | GENERIC_WRITE, 0, 0, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, 0);
    
    	if(hSerial==INVALID_HANDLE_VALUE)
    	{
    		if(GetLastError()==ERROR_FILE_NOT_FOUND)
    		{
    			printf("Serial port does not exist\n");
    		}
    		printf("Other errors\n");
    	}
    
    	//setting parameters
    	dcbSerialParams.DCBlength = sizeof (dcbSerialParams);
    
    	//GetCommState is to retrieves the current control settings for a specific communications device.
    	if (!GetCommState(hSerial, &dcbSerialParams))
    	{
    		printf("Not GetCommState, not able to retrieves the current control\n");
    	}
    
    	dcbSerialParams.BaudRate = CBR_115200;
    	dcbSerialParams.ByteSize = 8;
    	dcbSerialParams.StopBits = ONESTOPBIT;
    	dcbSerialParams.Parity = NOPARITY;
    
    	//SetCommState configures a communications device according to the specifications
    	//in DCB. The function reinitializes all hardware control settings but it does not
    	//empty output or input queues
    	if (!SetCommState(hSerial, &dcbSerialParams))
    	{
    		printf("Not SetCommState, cannot configures serial port according to DCB specifications set\n");
    	}
    
    	//setting timeouts
    	timeouts.ReadIntervalTimeout = 40;
    	timeouts.ReadTotalTimeoutConstant = 40;
    	timeouts.ReadTotalTimeoutMultiplier = 40;
    	timeouts.WriteTotalTimeoutConstant = 40;
    	timeouts.WriteTotalTimeoutMultiplier = 40;
    
    	//SetCommTimeouts set the time out parameters for all read and write operation
    	if (!SetCommTimeouts(hSerial, &timeouts))
    	{
    		printf("Not SetCommTimeouts, cannot set the timeout parameters to serial port\n");
    	}
    
    	//reading data
    	//ReadFile reads data from the specified file or i/o devices.
    	printf("The content inside the file: \n\n");
    	if(!ReadFile(hSerial, szBuff, maxBytes, &dwBytesRead, NULL))
    	{
    		 printf("error\n");
    	}
    	else
    	{
    		fp = fopen("c:\\new.txt", "w");
    		while (ReadFile(hSerial, szBuff, maxBytes, &dwBytesRead, NULL))
    		{
    			
    			for (i = 0; i < dwBytesRead; i++)
    			{
    				if (szBuff[i] == 10 || szBuff[i] == 13)
    				{
    					fprintf(fp, "\n");
    					printf("\n");
    					break;
    				}
    				else
    				{
    				fprintf(fp, "%c", szBuff[i]);
    				printf("%c", szBuff[i]);	
    				}
    			}
    						 
    		}
    
    		fclose(fp);
    
    	CloseHandle(hSerial);
    
    	}
    }



    This is my codes for thw "writing" side (The program will read the content inside a textfile called "helloworld.txt" and write it line by line to the serial port)
    Code:
    #include "windows.h"
    #include <stdio.h>
    #include <io.h>
    #include <conio.h>
    #include <stdlib.h>
    
    #define maxBytes 111
    #define MAX 256
    
    int main()
    {
    	HANDLE hSerial;
    	DCB dcbSerialParams = {0};
    	COMMTIMEOUTS timeouts = {0};
    	DWORD dwBytesWrite = 0;
    	int i;
    	char szBuff[maxBytes];
    	char stemp[MAX];
    	FILE *fp;
    
    
    	//opening the serial port
    	hSerial = CreateFile("COM1", GENERIC_READ | GENERIC_WRITE, 0, 0, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, 0);
    
    	if(hSerial==INVALID_HANDLE_VALUE)
    	{
    		if(GetLastError()==ERROR_FILE_NOT_FOUND)
    		{
    			printf("Serial port does not exist\n");
    		}
    		printf("Other errors\n");
    	}
    
    	//setting parameters
    	dcbSerialParams.DCBlength = sizeof (dcbSerialParams);
    
    	//GetCommState is to retrieves the current control settings for a specific communications device.
    	if (!GetCommState(hSerial, &dcbSerialParams))
    	{
    		printf("Not GetCommState, not able to retrieves the current control.\n");
    	}
    
    	dcbSerialParams.BaudRate = CBR_115200;
    	dcbSerialParams.ByteSize = 8;
    	dcbSerialParams.StopBits = ONESTOPBIT;
    	dcbSerialParams.Parity = NOPARITY;
    
    	//SetCommState configures a communications device according to the specifications
    	//in DCB. The function reinitializes all hardware control settings but it does not
    	//empty output or input queues
    	if (!SetCommState(hSerial, &dcbSerialParams))
    	{
    		printf("Not SetCommState, cannot configures serial port according to DCB specifications set.\n");
    	}
    
    	//setting timeouts
    	timeouts.ReadIntervalTimeout = 40;
    	timeouts.ReadTotalTimeoutConstant = 40;
    	timeouts.ReadTotalTimeoutMultiplier = 40;
    	timeouts.WriteTotalTimeoutConstant = 40;
    	timeouts.WriteTotalTimeoutMultiplier = 40;
    
    	//SetCommTimeouts set the time out parameters for all reand and write operation
    	if (!SetCommTimeouts(hSerial, &timeouts))
    	{
    		printf("Not SetCommTimeouts, cannot set the timeout parameters to serial port.\n");
    	}
    
    	//Writting data
    	//WriteFile write data from the specified file or i/o devices.
    	printf("The content inside the file: \n\n");
    	fp = fopen("c:\\helloworld.txt", "r");
    	while ((fgets(stemp, MAX, fp)) != NULL)
    	{
    		i = sprintf(szBuff, "%s", stemp);
    		if (!WriteFile(hSerial, szBuff, maxBytes, &dwBytesWrite, NULL))
    		{
    			printf("Serial port cannot write file.\n");
    		}
    		else
    		{
    				printf("%s", szBuff);
    		}
    	}
    	fclose(fp);
    	CloseHandle(hSerial);
    }
    I know that this is just a small program but how do i make the "reading" program poll only when the "writing" program is trying to send data?

    Someone please help, new in serial port.

  2. #2
    Deathray Engineer MacGyver's Avatar
    Join Date
    Mar 2007
    Posts
    3,211
    Uh, if it's a DOS program, why are you including Windows.h? The black box of fun that comes with Windows XP isn't really DOS...

    You might want to make sure you understand what you're programming for, before you get too much into it. This technically isn't a C++ issue, so this may get thrown into another section of the forums by the moderators.

    Oh, and welcome to cboard.

  3. #3
    Registered User
    Join Date
    Aug 2006
    Posts
    99
    Quote Originally Posted by infineonintern View Post
    I know that this is just a small program but how do i make the "reading" program poll only when the "writing" program is trying to send data?
    In general, that statement is just about 100% backwards. In almost all data servers, serial, Ethernet, whatever, the READER (Client) sends out poll messages, and the WRITER (Server) responds to them.

    You should have your 'Writer' sit and wait for a go-ahead sequence of characters from the reader, before it begins spewing forth data. That way, start up order isn't important.

    You also need the bidirectional communications in both programs, and should probably do transfers in discrete blocks, so that you can detect errors (simple block checksums can work here), and re-transmit blocks as required.

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