Any one know how to access individual pins on the parallel port in Linux and what the voltage levels are? If I find something before someone replies I'll post again.

the pins run at 5v, most of them with a very low current though, so are only useful for data, not power (you can gang together a big bunch pins (say the output port) and power a small IC if you really want.

it's pretty easy to set individual pins, but the last time i did it was 1 year ago for my degree project (a fully functional oscilloscope capture engine).

i found the "parapin" wrappers useful for a lot of interaction and that's also a good enough bit of source code to read through (it's easy enough to translate to C++ if need be)

one of my key resources was the BEyond Logic site, has shedloads of info (although mainly for win32 programming.. but it's very similar at register level. just need a different c library)

http://www.beyondlogic.org/index.html

Here is some code where the data lines lit some led lamps.


/* meter.c by Joseph W. Vigneau (joev@wpi.edu) (c)1994.
This program is covered under the GNU copyleft agreement.
*/

#include <stdio.h>
#include <unistd.h>
#include <errno.h>
#include <time.h>
#include "port.h"

float loadavg(void)
{
FILE *f;
char line[80];
float cpu = 0.0, totalcpu = 0.0;

if((f = popen("/bin/ps -aux","r"))==NULL) {
fprintf(stderr,"Couldn't fork /bin/ps.\n");
exit(1);
}

fgets(line, 80, f);
while(!feof(f)) {
sscanf(line,"%*s %*d %f",&cpu);
totalcpu += cpu;
fgets(line, 80, f);
}
/* printf("TOTAL: %f\n",totalcpu); */
pclose(f);
return totalcpu/100.0;
}


main()
{
unsigned char lights;
float ave;
char dir = 0;
char foo[10];
register unsigned char numlights, i;

if(ioperm(0x378,1,1)) {
fprintf(stderr,"ioperm error.\n");
exit(1);
}

while(1) {
ave = loadavg();
numlights = (int)(ave*8.0);
/* printf("ave = %f, numlights = %d\n",ave, numlights); */

lights = 0;
for(i=0;i<numlights;i++)
lights |= (1<<i);

port_out(0x378, lights);
usleep(750000L);
}
}

This program has to be suid root, due to the ioperm call.

not a great example really, there's a lot of excess junk there, and appears to actually use an additional bit of code to set the lines (from the ports.h include statement) to set the lines you'll want to get familiar with the outb command

I am running something much simpler that I'm sure you've seen before (lptout) but my problem I have is that it works on my laptop, but on my desktop, I get a segmentation fault. Anyone have any idea how to fix this?

please don't drag up unlrelated threads. i'd suggest you create a new thread in Programming, and add a lot more information, e.g. gdb backtraces etc...