From joev@mikasa.WPI.EDU Sun Jan  1 18:34:40 EST 1995
Article: 144 of comp.os.linux.development.system
Path: bigblue.oit.unc.edu!concert!gatech!bloom-beacon.mit.edu!news2.near.net!news.mathworks.com!bigboote.WPI.EDU!mikasa.WPI.EDU!joev
From: joev@mikasa.WPI.EDU (Joseph W. Vigneau)
Newsgroups: comp.os.linux.development.system
Subject: My LED performance meter thing...
Date: 1 Jan 1995 23:18:28 GMT
Organization: Worcester Polytechnic Institute
Lines: 147
Message-ID: <3e7d84$or5@bigboote.WPI.EDU>
NNTP-Posting-Host: mikasa.wpi.edu

Last week, someone wrote here asking about robotic contol via Linux... I
responded explaining how I used the parallel port to control a sort-of
"performance meter".  I've recieved a lot of requests on how I did this.
Here's the story:

Last year, at school (WPI), Silicon Graphics brought this huge 18-wheel
truck that is basically a demonstrationmobile.  Inside it had Indys,
Crimsons, and some of their big machines like a couple of Onyxes and an
*monsterous* Power Challenge.. I'm relatively young (17 at the time), and
I'd never seen a computer this big before: It looked like an oversized
refrigerator, with cooling ducts running in and out of it!  On the front of
this beast, was a little LCD backlit readout about the size of my HP-48G's
display.  It was labeled "CPU Activity", and had a little bar chart showing
how hard each processor was working.  I thought it would be cool to have one
of these mounted on my Linux box :)

I finally got a computer of my own this past November, and finally got to run
Linux on my own, instead of administering it for a number of people on my
floor.  I had a Shack attack, and went to Radio Shack, and picked up the 
following items: a breadboard, a 10-bar LED, breadboard wires, and a 
package of assorted resistors. [Side note: While at the Shack with a few of
my suitemates, we were way in back in the component section (the only good
part of the store any more), and were approached by a lady who thought we
were employees there :). Back to the project.]

It was wired up like this, via the parallel port:

                                pin 20 (ground)
                                  |
               150ohm     LED     |
pin 2 (D0) ----/\/\/------|>|-----+
                                  |
pin 3 (D1) ----/\/\/------|>|-----+
                                  |
pin 4 (D2) ----/\/\/------|>|-----+

            [...]
                                  |
pin 9 (D7) ----/\/\/------|>|-----+

Note: 2 of the LEDs weren't connected.

Now, the software part:

Two files were used: the first is a routine written by a roomate
(damianf@wpi.edu) used to blast raw bytes at a port, and read them. Please
contact him for more info, or if you want to use it in a progrm of your own.

static inline int port_in( int port )
{
   unsigned char value;
  __asm__ volatile ("inb %1,%0"
                    : "=a" (value)
                    : "d" ((unsigned short)port));
   return value;
}

static inline void port_out( unsigned short int port, unsigned char val )
{
  __asm__ volatile (
                    "outb %0,%1\n"
                    :
                    : "a" (val), "d" (port)
                    );
}

I originally wanted to use the load average to determine how many of the
LEDs lit up, but realized that it was only updated every minute.. I wanted a
display similar to xload or xosview, but I really coun't figure out how they
were determined.. What I ended up doing was reading the output of 'ps aux',
and summing up the %CPU column.  I then converted that into a number
representing how many LEDs should light, and blast it at the printer port.

NOTE: I wrote and built this thing in a bout 90 minutes, so it's quick and
dirty, and not at all as elegant as I hoped it to be.

Here's the program:

/* 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.

Good luck, and have fun! Your mileage may vary.. If this makes your computer
explode or something, I'm not responsible, etc..  If you improve upon this,
post it here, so everyone else can see!

-- 
joev@wpi.edu               WPI Computer Science '97                      Linux!
             <a href="http://www.wpi.edu/~joev"> Click Here! </a>