> Right, it's the MIE device, which we already emulate in MAME for Naomi. (I think > recent versions of Demul do too).
Of course, that MCU was reversed by Demul team, then shared with MAMEdevs.
> There *is* resident firmware - we have the version for Naomi/Naomi2, I don't know if > it's the same one in Hikaru.
I beleive firmware is the same, READ8_MEMBER(mie_device::read_78xx) { // Internal rom tests (7800) & 80 and jumps to 8010 if non-zero
This was not used in Naomi, but Hikaru uses this, SH4 write 80 to 7800 after uploading program into MIE RAM to start it.
And yes, MIE in Hikaru is memory mapped: 80xxxx - access to ports of MIE 82xxxx - first 32k of z80 memory space 83xxxx - second 32k offset must be >>1
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