Path: utzoo!attcan!uunet!wuarchive!zaphod.mps.ohio-state.edu!ncar!ames!vsi1!octopus!stever
From: stever@Octopus.COM (Steve Resnick )
Newsgroups: comp.os.msdos.programmer
Subject: Re: Turbo C Interrupt Question
Message-ID: <1990Oct10.163937.8166@Octopus.COM>
Date: 10 Oct 90 16:39:37 GMT
References: <32923@nigel.ee.udel.edu>
Reply-To: stever@octopus.UUCP (Steve Resnick )
Organization: Octopus Enterprises, Cupertino CA
Lines: 32

In article <32923@nigel.ee.udel.edu> shearer@cis.udel.edu (Rob Shearer) writes:
>
>I have hooked the INT 8 interrupt (IRQ 0, Clock_Tick Interrupt) on my 
>PC.  Normaly I want the routine to happen on a set schedule..  but there
>are times that I want the INT 8 routines to occur out of sync and I call
>it from another part of my code with a geninterrupt(8);  (I take care
>of the REAL Clock no matter what...).  Can you Gurus inform me how to
>detect if the interrupt was hardware or software driven??  It is all
>probably in the PIC... but ALL my reference books basically inform me that
>there IS such a think as the PIC.  
>
>(Before anyone tells me to hook INT 1C instead..  I NEED INT 8, that is why
>I hooked it...  and if I can differentiate between a hw and sw interrupt
>then life is fantastic!)
>

According to Joe Campbell in "C Programmer's Guide to Serial Communication"
the 8259 PIC has a register which indicates any pending interrupts. To
read this input a byte from port 21H, since you want IRQ0 (Timer) test bit
0 to see if it is set. If it is, you have a pending timer interrupt, otherwise
the int 8 was called via a software int. I haven't tried this, but it seems
pretty straight forward. 

Hope this helps....
Steve


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