Hello,

I am trying to write a small user land program for
transfer of data b/w 2 computers via parallel port. I
am using the Linux 2.4 parport system.

While receiving data, I get the same character
repeated multiple time, if I send 'good' I receive
'gggoooooddd' at the other end. I tried using
select(fd +1, &rfds, NULL, NULL, NULL); along with
PPWCTLOIRQ and PPWCONTROL, but I was not able to catch
any interrupt. I do not know what I am doing wrong.
Pls help....


/*CODE for transmitting data*/

#include<fcntl.h>
#include<stdio.h>
#include<errno.h>
#include<sys/ioctl.h>
#include<linux/ppdev.h>
#include<linux/parport.h>
#include<unistd.h>
#define BASE 0x378
int main(void){
int fd;
int mode;
char buf;
size_t got = 1;
int fd1, j=0;
int dir =0;// direction is 0 coz we need to transmit

/*Open the serial port for writing*/
fd = open ("/dev/parport0" , O_RDWR);

/* Open the file in which data to be transmitted is
present*/
fd1 = open("par",O_RDONLY);

/*gain access or permission for the port*/
if (ioctl (fd, PPCLAIM))

/*assign mode */
mode = IEEE1284_MODE_COMPAT;

/*set the desired mode*/
ioctl (fd, PPNEGOT, &mode);

/*set the direction of data flow(write) */
ioctl(fd, PPDATADIR, &dir);

/*until 1 or more character is there to read in the
file*/
for (;got == 1 {

/*read from the data file*/
got = read (fd1 , &buf, 1);

/*Write to the serial port*/
ioctl (fd, PPWDATA, &buf);

/*print the written data */
fflush(stdout);
printf("%c\n", buf);

/*delay a bit*/
usleep(1000);

/*output a value to control register*/
ioctl(fd, PPWCONTROL, &j);
j++;

/*if 5th bit of Control register is set, the data
lines cannot output data but they can only read, hence
j is changed from 1 to 31. i.e all the 4 bits of
control register are used*/
if(j == 31)
j=0;

}
}

/*End of code for transmitting data*/

I am printing out the received data in the CODE for
receivng data.

/*CODE for receiving data*/
#include<fcntl.h>
#include<sys/ioctl.h>
#include<linux/ppdev.h>
#include<linux/parport.h>
#include<stdio.h>
#include<sys/times.h>
#include<sys/types.h>
#include<sys/unistd.h>
#include<signal.h>

int fd;

/* this catcher() func is invoked when ctrl-C is
pressed*/
catcher(){
ioctl(fd, PPRELEASE);
exit();
}

int main(void){

int retval;
char buf;
int dir = 1; //since we are receiving data,
direction should be 1
int mode = IEEE1284_MODE_COMPAT; //used as a
parameter to set mode
char ch;

/* Open the serial port */
fd = open("/dev/parport0" , O_RDONLY );

/*catcht ctrl-c*/
signal(SIGINT, catcher);

/*gain access or claim the parallel port*/
ioctl(fd , PPCLAIM);

/*set the desired mode of communication(COMPAT in
this case*/
ioctl(fd, PPSETMODE, &mode);

/*set the direction of transmission(reception in
this case) */
ioctl(fd, PPDATADIR, &dir);

/*read value from Control register */
ioctl(fd, PPRCONTROL, &ch);
printf("Intial values of Control register is %d\n",
ch);

/*read value from Status register */
ioctl(fd, PPRSTATUS, &ch);
printf("Intial value of status register is %d\n",
ch);

while(1){
printf("B4 read{");//before reading from data
register

/*read value from Status register */
ioctl(fd, PPRSTATUS, &ch);
printf("Status->%d", ch);

/*read value from Control register*/
ioctl(fd, PPRCONTROL, &ch);
printf("Control->%d}\t",ch);

/* READ the Sent Data from data register*/
ioctl(fd, PPRDATA, &buf);
printf("Data->%c\t",buf);

printf("After read{"); // after reading from data
register

/*read from Control register*/
ioctl(fd, PPRCONTROL, &ch);
printf("Control->%d",ch);

/*read from Status register*/
ioctl(fd, PPRSTATUS, &ch);
printf("Status->%d}\n", ch);

/*delay a bit*/
usleep(1000);
}

return 0;
}
/*END of CODE for receiving data*/

------------SAMPLE OUTPUT-------------

Intial values of Control register is 12
Intial value of status register is 127

B4 read{Status->127Control->12} Data->ÿ After
read{Control->12Status->127}
B4 read{Status->127Control->12} Data->J After
read{Control->12Status->127}
B4 read{Status->127Control->12} Data->J After
read{Control->12Status->127}
B4 read{Status->127Control->12} Data->J After
read{Control->12Status->127}
B4 read{Status->127Control->12} Data->e After
read{Control->12Status->127}
B4 read{Status->127Control->12} Data->e After
read{Control->12Status->127}
B4 read{Status->127Control->12} Data->s After
read{Control->12Status->127}
B4 read{Status->127Control->12} Data->s After
read{Control->12Status->127}
B4 read{Status->127Control->12} Data->u After
read{Control->12Status->127}
B4 read{Status->127Control->12} Data->u After
read{Control->12Status->127}
B4 read{Status->127Control->12} Data->s After
read{Control->12Status->127}
B4 read{Status->127Control->12} Data->s After
read{Control->12Status->127}
B4 read{Status->127Control->12} Data->s After
read{Control->12Status->127}
B4 read{Status->127Control->12} Data->! After
read{Control->12Status->127}
B4 read{Status->127Control->12} Data->! After
read{Control->12Status->127}

----------END of output---------------