Message-Id:	<199602282142.VAA00540@mailbox.rmplc.co.uk>
Comments:	Authenticated sender is <lloyd AT mailbox DOT rmplc DOT co DOT uk>
From:	"Matthew Lloyd" <lloyd AT rmplc DOT co DOT uk>
Organization:	Private
To:	djgpp AT delorie DOT com
Date:	Wed, 28 Feb 1996 21:33:21 +0000
Subject:	Writing PM and RM interrupt handlers in assembler
Reply-to:	lloyd AT rmplc DOT co DOT uk

Dear All,
   I'm using DJGPP v2 (very impressive it is too), and I'm converting 
a program which makes use of the timer interrupt and the SB 
interrupt.
   Since this program eventually will become a commercial product, 
I'd like to write the handlers for these interrupts in assembler (as 
advised in the FAQ). Are there any examples around of assembler IRQ 
handlers? I've seen the C examples in pctime13.zip and sb_05.zip, but 
I really need to use assembler. I'd be most grateful if someone could
post me an example since I'm rather confused about how to:
      i) Load the application's data selector into DS when the 
         interrupt procedure starts - where does the value come from?
     ii) Call the previous interrupt handler; should I call the old 
         PM vector, the old RM vector, and... how?
    iii) Transfer data to/from the real-mode IRQ handler
     iv) Call the previous IRQ handler from the real-mode handler

   Any help is much appreciated.
   Thanks,


   Matthew Lloyd.

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