Path: utzoo!attcan!uunet!samsung!zaphod.mps.ohio-state.edu!mips!apple!mattd
From: mattd@Apple.COM (Matt Deatherage)
Newsgroups: comp.sys.apple
Subject: Re: Error reporting under Prodos 8.
Message-ID: <38729@apple.Apple.COM>
Date: 18 Feb 90 20:14:57 GMT
References: <8190@wpi.wpi.edu> <15800070@ux1.cso.uiuc.edu>
Organization: Apple Computer Inc, Cupertino, CA
Lines: 49

In article <15800070@ux1.cso.uiuc.edu> cs225af@ux1.cso.uiuc.edu writes:
>
>
>If you just need to send an error back to an Applesoft BASIC program, to
>be trapped by an ONERR GOTO routine:
>
>LDX #err
>JMP $D412
>
>will do the trick.  It calls the routine Applesoft uses to generate its own
>errors.  Set the error code to whatever you want, and your ONERR GOTO
>can check for it w/ PEEK (222).  Also:
>
>JMP $DD76		generates a ?TYPE MISMATCH ERROR
>JMP $DEC9		generates a ?SYNTAX ERROR
>
>all this may not be too clean, but under Applesoft it works like a charm.
>If this isn't what you were asking, just ignore all the above.   =)
>
>-- rubio

Jumping to internal AppleSoft entry points is still not the world's best
idea, no matter how unlikely they are to change.  It's even a worse idea
when dealing with ProDOS, because AppleSoft in ROM doesn't know how to handle
MLI error codes.

There are three routines you should consider.  All are entered through
BASIC.SYSTEM's global page at $BE00.

BADCALL converts MLI error codes into BASIC.SYSTEM error codes (the ones
ONERR GOTO routines expect).  It takes the MLI error code in the A register
and returns the BASIC.SYSTEM error code in A.  Save other registers if you
need them, just in case.  The entry point, according to the P8 Technical
Reference Manual (where all this is discussed) is $BE8B.

ERROUT is vectored through $BE09.  It takes an error code in the Accumulator,
and sends it to an ONERR GOTO routine if one exists or otherwise prints the
appropriate BASIC.SYSTEM error message (or AppleSoft message, I guess).

PRINTERR is vectored through $BE0C.  It takes an error code in the A register
and prints the appropriate error message; it does not call ONERR GOTO routines
if they exist.

-- 
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Matt Deatherage, Apple Computer, Inc. | "The opinions represented here are
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