Date: Sat, 10 Sep 1994 13:06:30 -0700 (PDT)
From: "Frederick W. Reimer" <fwreimer AT crl DOT com>
Subject: Re: callbacks and wrappers
To: Kimberley Burchett <OKRA AT max DOT tiac DOT net>
Cc: DJGPP Mailing List <djgpp AT sun DOT soe DOT clarkson DOT edu>

On Sun, 4 Sep 1994, Kimberley Burchett wrote:
>   I was looking over some code someone wrote for DJGPP that installed an 
> interrupt handler and it allocated a real mode callback and an iret 
> wrapper... what are those?
> 							Kim

Since I don't think anyone else responded yet, I'll take a shot at an 
answer (although I don't profess to be an expert!).

There are several interrupt and callback allocation routines in go32, and 
I'm only familiar with a few so I'll go over those.  The 
_go32_dpmi_allocate_real_mode_callback_retf() function allocates a 
real mode address that when called (from a real mode program such as a 
TSR or driver) will transfer control to a protected mode function that 
you write.  This is useful if you call a real mode driver and whatever it 
does requires a real mode address for a callback function.  The stuff I'm 
messing around with involves a packet driver, which will call a real mode 
function whenever a packet is received by the network card in my 
computer.  Since DJGPP programs are protected mode, the 
..allocate_real_mode_callback.. functions are required, since passing the 
TSR a protected mode address would be useless.  The ...iret function is 
similar, except that it uses an IRET return instead of a normal return.

I'm not sure about the interrupt installer because I have no use for this 
(yet) and have not gotten into it.  Hope this helps! (and I'm not wrong!).


Fred Reimer

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