Message-Id: <199602282141.VAA00478@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.