Zac67 wrote:
Sigh...
Look, any chipmem access by the chipset works like this:
- Agnus generates the address to the chip bus (for the 'DMA')
- the data gets transferred to the chip that needs it
All address registers for the custom chips reside within Agnus (hence its name from Address Generator). The registers are 21 bits wide and the address bus is 21 bits wide (not precisely since we address words/longwords, but that doesn't make a difference).
There's absolutely no way to make Agnus see more than 2 Megs - apart from redesigning it of course. A redesign would need
- additional address lines to CPU bus switch
- additional address or select lines for RAM control
- enlarged address registers
- additional or larger RAM chips
something tells me that you can't get away with only redesigning agnus. The custom chips themselves, when requesting data use 21 bit addresses ? so they should be upgraded as well for the extra address line ?
