Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!utgpu!water!watnot!watmath!clyde!rutgers!lll-lcc!seismo!mcvax!unido!tub!csch
From: csch@tub.UUCP
Newsgroups: comp.sys.atari.st
Subject: Re: receiving interrupts in an user prog - (nf)
Message-ID: <49500015@tub.UUCP>
Date: Fri, 3-Apr-87 17:32:00 EST
Article-I.D.: tub.49500015
Posted: Fri Apr  3 17:32:00 1987
Date-Received: Wed, 15-Apr-87 00:43:20 EST
References: <530@dutinfd.UUCP>
Lines: 27
Nf-ID: #R:dutinfd:-53000:tub:49500015:000:988
Nf-From: tub!csch    Apr  3 23:32:00 1987

I think, it has something to do with how the 68000 wants her
exception-handlers to terminate.

Your (almost any) C-compiler ends functions with a RTS instruction,
but exception-handlers MUST take care of register-contents, stack-
pointer (usp) and have to return with RTE (return from exception).

On the ST you may ONLY use the VBL-IRQ directly from C. Functions
queued in the VBL-QUEUE (pointer to is $456 (points to $4ce))
may simply return with a RTS instruction.

If you want to use OTHER IRQ vectors you have to add a simple
assembly-language subroutine like

	movem.l	d0-a6, -(a7)	* save registers
	move.l	a7, sp_save	* save stack-pointer
	jsr	c_function	* call C function
	move.l	sp_save, a7	* restore stack-pointer
	movem.l (a7)+, d0-a6	* get registers back from supervisor-stack
	rte			* return from exception

NOTE!!!!! This is ONLY a SHORT example how you can START doing that stuff!!
		  ====         =======

Rgds.

Clemens (csch@tub.uucp = {unido | pyramid} ! tub ! csch)