From: David Hallberg <david DOT hallberg AT data DOT ing DOT hb DOT se>
Newsgroups: comp.os.msdos.djgpp
Subject: Interrupts on EPP-port
Date: Wed, 01 Mar 2000 11:28:57 +0100
Organization: University of Boras, Sweden
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To: djgpp AT delorie DOT com
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Reply-To: djgpp AT delorie DOT com

I'm having problem with getting my program to trigger on interrupts
from the parallel port (EPP-mode)
it works just fine when triggering from the timer, keyboard, and even
the networkcard (I have tried to switch IRQ between the networkcard and 
the parallel port, but it still only trigger in the network card and not
the parallel port)
I have read the discussion from 1998 initialized by  "Michel Gallant"
<mgallant AT NOSPAM DOT grassroots DOT ns DOT ca> 
about this,  but could not find any final, working example.

Code:

#include  <dpmi.h>
#include  <stdio.h>
#include  <unistd.h>
#include  <pc.h>
#include  <termios.h>

//#define VECTOR 8  // Timer
#define VECTOR 9  // keyboard
//#define VECTOR 13 // LPT2     IRQ 5
//#define VECTOR 15 // LPT1   IRQ 7


#define SET_BIT(x, b)   ((x) |= (1 << (b)))
#define CLEAR_BIT(x, b) ((x) &= ~(1 << (b)))
#define EPPADRESS 0x278

volatile int tics = 0;
unsigned int i, ii, inter = 0;
unsigned char regbyte, adr21;
unsigned long time1, time2;

     tic_handler()               // Interrupthandler
     {
       tics++;
     }
     
     int main()
     {
       _go32_dpmi_seginfo old_handler, new_handler;     // Structs for
handler

       new_handler.pm_offset = (int)tic_handler;        // give the
struct the new handler
       new_handler.pm_selector = _go32_my_cs();         // and a pointer
to this code

       printf("\nGrabbing interrupts");
                                                        // Reading old
handler
       _go32_dpmi_get_protected_mode_interrupt_vector(VECTOR,
&old_handler);

       _go32_dpmi_allocate_iret_wrapper(&new_handler);   // makes the
overhead for interrupthandeler
                                                        // Struct is the
new handler
       _go32_dpmi_set_protected_mode_interrupt_vector(VECTOR,
&new_handler);
       //_go32_dpmi_chain_protected_mode_interrupt_vector(VECTOR,
&new_handler);

       printf("\nStatusreg  %#x", inportb(EPPADRESS + 1));
       printf("\nControlreg %#x", inportb(EPPADRESS + 2));

       regbyte = inportb(EPPADRESS + 2);                       //
reading printerports old controll reg
       SET_BIT(regbyte , 4);    // enable intr. from port

       outportb(EPPADRESS + 2 , regbyte);       // writing the modified
reg.

       printf("\nStatusreg  %#x", inportb(EPPADRESS + 1));
       printf("\nControlreg %#x", inportb(EPPADRESS + 2));
       inter = enable();                    // enabeling interrupts


       time1 = rawclock();                       // get the current time
       tics = 0;
       while( tics < 1){}                        // wating for one
interrupt
       time2 = rawclock();
       printf("\nNumber of Interrupts during the execution: %d ", tics);
       printf("\nTime1: %D",time1);
       printf("\nTime2: %D",time2);
       printf("\nDIFF : %D",time2 - time1);
                                                 // puting back the old
handeler
       _go32_dpmi_set_protected_mode_interrupt_vector(VECTOR,
&old_handler);
       _go32_dpmi_free_iret_wrapper(&new_handler);
       getkey();
       return 0;

     }