Hi all,
I was wondering if it was possible to redirect some hardware access to some software routine .
The idea behind is to emulate hardware with software routines , of course it would be slower but it could be fine
for some apps :
- redirecting v9958 transaction on port98/99/9A/9B to gfx9000 : so gfx9000 could replace totally vdp.
- adding virtual ram on disk , by redirecting the mapper ports to software routines.
- enhancing psg games using better sound card.
- more generally making new hardware compatible with legacy software.
So it is not emulation with PC or FPGA but the MSX itself that would spy its own request and redirect them
to pure Z80 routines.
I try to think to a solution that does not require soldering or opening the computer , a cartridge at worst.
In a cartridge there could be logic that detects for instance an InOutRequest (IORQ) to some ports and raise
an interrupt if the condition is true. then the interrupt routine could deal with the request, but there are a lot
of problems or faster ways of doing things.
it is a bit like this emulation of a msx with a msx .
Maybe the thing is to have two Z80 , only one sees the real hardware and support the other that executes
legacy software.
I see two ways to do it , one purely software but it may be slow , an emulator on PC does like this, one is hardware
but it may be complicated or an overkill ( like putting a 100$ fpga )
I think the following projects are close :
- msx emulator in a TurboR of nyrryky, but i wonder if r800 is fast enough to insert an adaptation layer in sw.
- Z380 board , it is a second fast cpu that could execute legacy software , but it cant redirect hardware request, afaik
- aleste russian computer with vdp emulation with software.
I know Z280 can trap io request to some address routine but then it means Z80 cpu would have to be replaced.
And what about memory mapped peripherals ?
Well all this is just some thinking on how to make new hardware without disrupting compatibilitywith legacy sw.
if only all legacy sw were using bios routines !

I'd guess early computer pioneers didn't see that one coming... 