🚀 go-pugleaf

-- Hi,

I'm trying to write an interrupt handler that intercepts the keyboard 
interrupt. I've looked in the documentation that I have, and two 
alternative approaches seem to appear:

1. Write the handler as a procedure.

eg.

MODULE Int

VAR KbdInt [??:??] :ADDRESS;
(*seg ofs address for keyboard interrupt vector *)
    OldInt:ADDRESS;

(*$J+,C FF*) (*Save all regs, and have IRET *)

PROCEDURE Handler;
BEGIN
.....
END Handler;
(*$J-,C F0*) (*Normal procedure return conventions *)

BEGIN
OldInt:=KbdInt;
KbdInt:=ADR(Handler);
..... (*Bit of code where we want handler to work *)
KbdInt:=OldInt;
END Int.


However, there seems to be a possible way of doing it, by using the 
system procedures TRANSFER and IOTRANSFER Perhaps something like this??
(excuse the likely errors here!)

MODULE Int;

VAR
   Main,Handler:SYSTEM.Process;
   HandlerSpace:ARRAY[0..4096] OF BYTE;

CONST
     IntNo=16H;

PROCEDURE Handler;

VAR
   ExRegs:SYSTEM.ExtendedRegisters;

BEGIN; 
LOOP
    IOTRANSFER(Handler,Main,IntNo);
    ExRegs:=(SYSTEM.InterruptRegisters(Handler))^;
     
(* Handling Gunk down here *)

END;
END Handler;

BEGIN;
SYSTEM.NEWPROCESS(Handler,ADR(HandlerSpace),SIZE(HandlerSpace),Handler);
SYSTEM.TRANSFER(Main,Handler);

(*Code where we want all this to take effect *)

END Int.


There are several things that I can't seem to find explained very well:

If I want to write a keyboard interrupt handler, I will want to make it 
so that when my procedure returns, the registers are modified as if a 
call to the original handler had occured (at least most of the time, 
until the right keystroke(s) are entered) how do I do this?? 

The First example modifies the interrupt vector table directly. If i 
want to use this method, how do I calculate the address for any given 
interrupt??

And lastly: which of the above is the most practical/workable?? I would 
greatly appreciate a quick pointer in the right direction from someone 
who has tried this before :-)

Sincerely

-------------------------------------------------------------
|   Martin Harvey                                           |
|                  Term Time: mch24@cam.ac.uk               |
|                  Holidays:  mch24@harvey27.demon.co.uk    |
|                                                           |
|   Home page: http://www.pem.cam.ac.uk:81/mch24/home.html  |
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