Finding address of parallel port

[linux2k]

Hello,

I'm currently doing some parallel port programming. I would usually ask the user to enter the base address of the parallel port. Is there a way to write some C code that can find this out, instead of having to ask the user?

thanks.

[Franklin52]

Read the file /proc/ioports.

Regards

[linux2k]

I actaully know that its in /proc/ioports. But my programming skills arent that developed that I can search within files. Mayb you can show an example?

Also, there should be another method where I can ask the kernel instead of searching through the file, but I definitely have to idea how to do this one.

[Franklin52]

Ok, here's an example to obtain the address of the parallel port (I suppose you're doing that in C):

#include <stdio.h>

int main (int argc, char *argv[])
{
	FILE *pipein;
	char readbuf[11];

	if ((pipein = popen("grep parport /proc/ioports|cut -d' ' -f1", "r")) == NULL)
	{
		perror("popen");
		exit(1);
	}

	fgets(readbuf, 11, pipein);
	close(pipein);

	printf("%s", readbuf);
  	return(0);
	
}

If you're programming a device driver you can pass the grep command as a parameter to your driver.

Regards

[linux2k]

Hi Franklin52, thanks for showing how to do it. However, I want to take it a step further, by giving the user the option to enter the port address or search for it.
But I still have some questions about implementing it. I've asked the questions in the comments.

//Program to send a nibble of data to the lower four bits of the data port (Base address)
//Remember use the -O (the letter O) optimization flag to compile, becuase outb() and inb()
//are inline marcos. 
#include <stdio.h>
#include <sys/io.h>

#define all_on 15

//I wonder why not just int main() ? Seems to compile fine with main()  :)
int main(int argc, char *argv[])   
{
	FILE *pipein;  //defines stream
	char readbuf[10];  //buffer to store string
	int user_num=0;
	int baseaddr;
	char user_ans;
	
	printf("Would you like me to find the address range your parallel port [y/n]?: ");
	printf("\n");
	scanf("%c", &user_ans);
	
    if (user_ans =='y')
    {
    	
    	//Does a return of NULL mean failure? This never gets executed even when I
    	//put a fake file name.
    	if((pipein = popen("grep parport /proc/ioports|cut -d' ' -f1", "r")) == NULL)
    	{
    		close(pipein);
    		printf("Cant find it. You need to enter it manually\n");
			printf("Enter the base address of your parallel port: \n");
	        scanf("%x", &baseaddr);
    	}
    	
        //This always gets executed, regardless if grep finds the file or not. When it 
        //doesnt find the file, it outputs garbage for the string
		else 
		{
			fgets(readbuf, 10, pipein);
	    	close(pipein); //Could we also close the stream with pclose(pipein)?
	    	printf("The address range seems to be %s\n", readbuf);
	    	printf("Proceed to enter the base address\n");
	    	scanf("%x", &baseaddr);
		
		}
			
    }
    
    //User enters 'n'.
    else
    {
    printf("Enter the base address of your parallel port: \n");
	scanf("%x", &baseaddr);	
    }
    
    
	//Permission to access the data port of the parallel port
	ioperm(baseaddr,1,1);

    //-1 is escape charater
	while(user_num!=-1)
	{
		printf("\nEnter a hex digit in the range of 0 to F:\n ");
		scanf("%x",&user_num);
		
		if((user_num >=0x0) && (user_num <=0xF)) 
		{	
			outb(user_num,baseaddr);	
			
		}
		else
		printf("Not in range!\n");
		
	}

	//Just some after effects after the loop exits.Turns all LEDs OFF, ON, then OFF 
	outb(0,baseaddr);   	//OFF
	sleep(2);           	// 2 second delay
	outb(all_on,baseaddr);  //ON
	sleep(1);
	outb(0,baseaddr);   	//OFF
	
	//Gives up access
	ioperm(baseaddr,1,0);
	
	return 0;
	
}

I'm by no means a good programmer. My programs usually work and get the job done. However, it may not to it in the simplest way. Its a good thing I dont design circuits the way I write programs

[Franklin52]

//I wonder why not just int main() ? Seems to compile fine with main()

It's in this case not necessary, you don't use the arguments.

//Does a return of NULL mean failure? This never gets executed even when I
//put a fake file name.

This executes only when the popen function fails.

//This always gets executed, regardless if grep finds the file or not. When it
//doesnt find the file, it outputs garbage for the string

The example was just to show how you can obtain the address of the parallel port but with the right filename.

//This always gets executed, regardless if grep finds the file or not. When it
//doesnt find the file, it outputs garbage for the string

There's no problem if you use the right filename in your code and it's not necessary to ask for a manually input from the user.

An alternative is to pass the address to your prog:

/your_dir/your_progname `grep parport /proc/ioports|cut -d' ' -f1`

Regards