RE: software support for memory expansions
Date: 2001-08-08 09:14:29

Lack of software support has always been a reason why I've considered these
RAM expansions at a lower priority to building other things....

The two internal expansions: +60k/VCS (or +192k) and the one hosted on funet
(documented by Marko?), are both great, but neither offers a patched kernal
ROM which makes it easy. There's a patched GEOS version by YTM which the
+60k expansion, and DiskCopy and other tools for both.

My idea of key features that should be supported with Kernal jump-table
calls are:
detect (normal system should have no change, and should point to an RTS)
far JMP
far JSR
copy page (256bytes) from /to
compare page page (256bytes) from /to

With these at a minimum, even someone with only BASIC programming experience
could get things happening with a few pokes and an SYS.

With talk about SIMM based projects, is it worth while standardising a
calling method and JumpTable location which doesn't cause incompatibilities.
Assuming 20bit addresses, I'm thinking a JSR with
A= 4bit "from", 4bit "to" nibbles
Y= 8bit "from" page (hibyte)
X= 8bit "to" page (hibyte)
call to retun code by flags

One other option was to embed this functionality in USR which points to
nowhere, eg 
USR(0)=>detect (already RTS)
USR(1)=> far JMP

with AXY poked into the 7xx locations used for SYS calls

- Nick


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