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kosarev / z80

Fast and flexible Z80/i8080 emulator with C++ and Python APIs
MIT License
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Support IM0 #3

Open kosarev opened 3 years ago

kosarev commented 3 years ago

Aside of #2, this seems to be the only missing feature.

simonowen commented 3 years ago

Rather than asserting, could the default implementation behave as though FF is read from the bus to give RST &38? From what I remember from testing IM 0 and IM 1 behave the same if there's nothing providing an instruction on the bus. The timing might be 6T instead of 7T for ack.

kosarev commented 3 years ago

Certainly a good idea. 9ae1dad should implement it. Regarding timings: according to my copy of the Sean Young paper, IM 0 and IM 1 both take 13 ticks, which I understand means we have ack(7) write(3) write(3) here.

kosarev commented 3 years ago

Now that the assert() is removed, this looks more like an enhancement rather than a bug.