I just realized that this also partially works with OCS (Amiga 1000). It would essentially work like this. And technically anything the CPU cant reach is Expansion RAM. It's not a perfect fix for the 1000, but it could be a big improvement from its stock 512KB. Does mean putting an pSRAM chip on Skinny Willoe thought...
Amiga 1000:
Code:
$000000-$07FFFF 512KB Base Chip RAM (CPU+Chip)
$080000-$FFFFFF 15.5MB Expansion Chip RAM (Chip Only)
Stock Amiga 500/2000:
Code:
$000000-$0FFFFF 1MB Base Chip RAM (CPU+Chip)
$100000-$FFFFFF 15MB Expansion Chip RAM (Chip Only)
Stock Amiga 500+/600:
Code:
$000000-$1FFFFF 2MB Base Chip RAM (CPU+Chip)
$100000-$FFFFFF 14MB Expansion Chip RAM (Chip Only)
Amiga 500/2000/500+ with Xander
Code:
$000000-$1FFFFF 2MB Base Chip RAM (CPU+Chip)
$200000-$7FFFFF 6MB Extended Chip RAM (Opt. CPU+Chip)
$800000-$FFFFFF 8MB Expansion Chip RAM (Chip Only)
Stock Amiga 3000/1200/4000
Code:
$000000-$1FFFFF 2MB Base Chip RAM (Motherboard, CPU+Chip)
$200000-$FFFFFF 14MB Expansion Chip RAM (Chip Only)
This means all pointers for DMA are 24-bit. Just have to remember that the extended 8MB in chip is NOT the same 8MB that the CPU can see (which would be full of things like registers, ROM, Ranger RAM, etc.)
Code:
xxxxPTH High 9-bits of address
xxxxPTL Low 15-bits of address