Programmers Corner
David Empson
Copyright (c) 1994 Apple Users' Group, Sydney
Republished from Applecations, a publication of the Apple Users' Group, Sydney, Australia.
dempson@actrix.gen.nz
Source: Internet comp.sys.apple2
After booting directly into ProDOS 8, you'll receive an error when trying to allocate memory using the memory manager. This functionality and a work-around is documented in Apple //gs Toolbox Reference 1 (pg 12-17).
The error is returned by the MMStartUp call because MMStartUp is being called from a location which is not inside a valid handle. Bank 0 memory is not allocated if you boot ProDOS-8 directly.
Unfortunately, no sample code for the work around is provided. Here is some sample code in 65816 assembler to do the job.
clc
xce
rep #$30 ;16-bit mode
stz Bank0Hand ;Assume we didn't allocate a handle
stz Bank0Hand+2
_TLStartUp
pha
_MMStartUp
pla
bcc GotID
; If MMStartUp returns an error, bank zero hasn't been allocated yet - the user probably cold booted into ProDOS-8. Get a new Application user ID and allocate some of bank zero for myself. This should be freed before exiting (along with the user ID)
pha
pea $1000 ;ID type = application
_GetNewID
plx
bcs crash ;OUCH!
pha
pha ;Result space
pea $0000
pea $B800 ;Size
phx ;User ID
pea $C002 ;Fixed address
pea $0000
pea $0800 ;Address
_NewHandle
plx
ply
bcs crash ;Oh dear - major problem
stx Bank0Hand
sty Bank0Hand+2
pha
_MMStartUp ;Try again...
pla
bcc GotID
crash ;Do something ugly
GotID ;Store your user ID somewhere

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