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chaining interrupts

Posted on 1997-08-06
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Last Modified: 2008-03-06
How do I chain interrupts in C++? I am using Borland, and I want to use the tick timer.  Does the "interrupt handler" func handle this for me?
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Question by:kellyjj
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md041797 earned 50 total points
ID: 1166958
If you're talking about DOS, just use getvect to get the old interrupt vector and then setvect to install your handler.  Disable interrupts during setvect.  Your handler executes and then jmp to the old vect.  Reverse the process to install.


/* * * * * * * * * * * * * * *
NOTE: This is an interrupt service routine.  
You can NOT compile this program with
Test Stack Overflow turned on and get an
executable file that will operate correctly.
 * * * * * * * * * * * * * * */


#include <stdio.h>
#include <dos.h>
#include <conio.h>



#define INTR 0X1C    /* The clock tick interrupt */

#ifdef __cplusplus
    #define __CPPARGS ...
#else
    #define __CPPARGS
#endif

void interrupt ( *oldhandler)(__CPPARGS);

int count=0;

void interrupt handler(__CPPARGS)
{
/* increase the global counter */
   count++;

/* call the old routine */
      oldhandler();
}
      int main(void)
{
/* save the old interrupt vector */
   oldhandler = getvect(INTR);

/* install the new interrupt handler */
   setvect(INTR, handler);

/* loop until the counter exceeds 20 */
      while (count < 20)
      printf("count is %d\n",count);

/* reset the old interrupt handler */
   setvect(INTR, oldhandler);

   return 0;
}
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Expert Comment

by:md041797
ID: 1166959
Revise that.  setvect disable interrupts for you, so forget about that part.
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Author Comment

by:kellyjj
ID: 1166960
thanks,  
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