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From: higgin@cbmvax.commodore.COM (Paul Higginbottom)
Newsgroups: net.micro.amiga,comp.sys.amiga
Subject: Re: Capturing ^C
Message-ID: <971@cbmvax.cbmvax.commodore.COM>
Date: Sat, 8-Nov-86 12:32:48 EST
Article-I.D.: cbmvax.971
Posted: Sat Nov  8 12:32:48 1986
Date-Received: Sun, 9-Nov-86 05:39:39 EST
References: <2210@mtuxo.UUCP> <46@uw-atm.UUCP>
Reply-To: higgin@cbmvax.UUCP (Paul Higginbottom)
Distribution: net
Organization: PDH, Inc.
Lines: 86
Xref: watmath net.micro.amiga:5783 comp.sys.amiga:6
Summary: followup to James Synge's comments...

In article <46@uw-atm.UUCP> james@uw-atm.UUCP (James M Synge) writes:
>In article <2210@mtuxo.UUCP>, tas@mtuxo.UUCP (t.skrobala) writes:
>> Is there a way to capture ^C signals on Amiga in a manner analagous to
>> UNIX signal()?  I'd like to be able to abort recalcitrant programs with
>> ^C, but do some cleanup before exiting.  Thus I'd like a function to be
>> called when ^C is typed.  My reading of the ROM Kernel Manual suggests
>> that SigExcept() is the key, but, in the example below, my onintr()
>> function only gets called once (with d0 set to 0), when SetExcept() is
>> called, and never thereafter; ^C's are ignored.
>
>I've tried writing an exception handler and had some problems.  One thing
>I notice you're not dealing with in your assembly section is the fact that
>you don't know what state your registers are in, except D0 and A0, which
>contain the signal mask and address of your ExceptData.  SO, when your
>code is adding 1 to hadIntr, you don't know where that 1 is being
>added.  It is some offset from (A4), but, since A4 is in an unknown state,
>we don't know where that is.
>

This is not really true.  The "rules" of the OS dictate that routines
leave registers untouched except d0/d1/a0/a1 which are used for passing
args and results and cannot be guaranteed to be munged during some call.
Thus, a4 should always be in a healthy state for a program's assembler
sections to access any variables in the C or assembler parts.  The
linker converts:

	move.w	_stuff,d0

into

	move.w	(a4)_stuff,d0

(please excuse assembler inaccuracies, I do as little as possible)

>> If I don't
>> call SetExcept(), ^C produces an immediate exit (after I hit RETURN to
>> satisfy the read()).
>
>This is because the Manx io routines check for ^C every time (unless you
>set an external variable whose name I cann't remember).
>

The variable is Enable_Abort, and to disable Manx's checking of CTRL-C
during sys and std i/o - you need to set it to 0.  E.g:

main()
{
	extern short Enable_Abort;

	Enable_Abort = 0;	/* no more ctrl-c aborts */
	...
}

However, you can STILL check for CTRL-C's conveniently via the Chk_Abort()
function provided in the Manx system. E.g:

...
	extern long Chk_Abort();

	... some i/o loop ...
	{
		if (Chk_Abort())
		{
			break;	/* leave the loop */
		}
		....
	}

	... cleanup here ...

>> Thanks,
>> Tom Skrobala AT&T Information Systems  ihnp4!ariel!tas
>
>My pleasure,
>-- 
>---------------------------------------------------------------------------
>James M Synge, Department of Atmospheric Sciences, University of Washington
>VOX: 1 206 543 0308 (Work)   1 206 455 2025 (Home)
>UUCP: uw-beaver!geops!uw-atm!james
>ARPA: geops!uw-atm!james@beaver.cs.washington.edu

Mine too,

	Paul Higginbottom, my house, Exton, PA.

Disclaimer: I work for myself, and my opinions are my own.