Brane2 wrote:
I don't understand. With ULA2+IPC approach, you get to do whatever you want. You don't need to care abut IPC protocol.
If you want to emulate the form ( and thus form 2 DIP40-ized PCBs and no extr wires between them) , you just have to use existing ULA2<->SPC comm lines in whichever way you want.
The main question in replacing the 8302 is how much of the original 8302 you want to emulate, so that it is transparent to the OS.
The IPC interface is basically two bits that are bit-banged serial with a bit of a strange twist. So whatever you want to do keeping IPC operation transparent to the OS, needs to implement this strange and limiting thing. This may be OK for what the original IPC does, but if you want to extend the feature set, it is not at all reasonable to do it through a two bit bitbanged thing. So, what I meant was, have an additional mechanism based on register (byte wide) read write for any added functions, since one needs an extension driver for those anyway.
superHermes was the exception to this rule since at the time there were no real options to replace ULA2, so with a lot of clever programming and OS extensions, an extra fast serial port plus a mouse serial port and other features were added, all accessed through the IPS interface, but it needs a nextra flying lead with the EXTINT signal to get the IPC interrupt working right (there seems to be an option for that in the 8302 but it seems to be buggy). If you are replacing the 8302, you get the extra byte sized register option, which superHermes did not have.