Apple GEOS Zeropage Usage

The Hitchhiker's Guide To GEOS contains no section on zeropage usage. However the section on public GEOS variables shows variables at locations in the range $53 - $78.

Some reverse engineering on existing applications shows that the GEOS pseudoregisters r0 - r15 are mapped to the locations $00 - $1F. This is very plausible as they are mapped to the locations $02 - $21 on machines with a 6510 (where the location $00 and $01 can't be used).

An Apple II emulator instrumented to create a zeropage usage statistics seems to indicate that the locations $80 - $FF are not used by the GEOS Kernal. Therefore the location $80 was choosen as base address of the cc65 zeropage memory area.

cc65/apple2/geoszeropage.txt · Last modified: 2012-03-01 18:52 by
Except where otherwise noted, content on this wiki is licensed under the following license: CC Attribution 3.0 Unported
Recent changes RSS feed Donate Powered by PHP Valid XHTML 1.0 Valid CSS Driven by DokuWiki