Emulator

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Jim e
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Post by Jim e »

CoBB wrote:
benryves wrote:Do you have any hints/tips for how much of the hardware needs to be emulated before it even vaguely works, or how you built the emulator? :)
Well, the 83+ can obviously boot without any kind of flash functionality implemented. ;) It can also live without the link assist (which isn’t used by the BE anyway). You definitely need the keyboard, the LCD, the interrupts, the paging mechanism and port 2 reporting a plain plus. The flash can behave as plain ROM and ignore all writes. That should be sufficient to get it running.
I've been making DS version of the emulator. Because of the DS's limitations I had to rewrite all hardware. I was using someone else Z80 core, so it only took me like 2 hours to reimplement everything to make TI-OS run. To be honest I like some of the design better than wabbits. I guess it's easier now that I have experience.


Flash can be ignored.
LCD is needed but thats easy.
Memory mapping is important right off the bat. (Remember boot Mapping)
Link only needs to return a value of 3.
Key port doesn't need to be implemented to get to the homescreen.
Status port 02 needs to read something like $3B.
Interrupts only need to occur at a steady rate. Neither Masking them nor proper acknowledging is important at first. Just every 100th of a second, if the CPU is not DI, perform an RST 038h.
Port 04 needs to say that ON is being pressed.

That will get TI-OS running.

If you plan on implementing 84+ properly, theres a LOT planning that you'd need to do. The hardware there can interrupt at every instruction, CPU speed is variable, flash hardware is different, and TI-OS uses a different op-amp factor(every model has a different contrast setting).

Theres also the nastiness with the fact that theres a settable tstate delay. But it's likely there because SE's Flash chip is much slower than the 83+'s, running at 15mhz really does push it.
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benryves
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Post by benryves »

Thanks a lot, both of you, very useful hints. :)
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