PC98 core

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siskavard
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Re: PC98 core

Unread post by siskavard »

Thanks for the info. I'm still rooting for ya!
Mosojol
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Re: PC98 core

Unread post by Mosojol »

Is this still being worked on? It would be amazing to have PC98 simulation!
puu
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Re: PC98 core

Unread post by puu »

I'm proceeding very slowly.
Rewriting to ao486 base is very difficult, so I'm thinking of going with Zet base as before, but since the BIOS image for 8086 / V30 machine is very difficult to obtain, I think that there is no choice but to write a compatible BIOS. I have.
In that case, it seems that even DOS applications use the internal code of ROM BASIC, so it seems to be important how compatible the BIOS is created.
I have never written a program that handles segments, so I am doing trial and error, including how to write it in assembler.
ayanami0
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Re: PC98 core

Unread post by ayanami0 »

thank you puu.
Mosojol
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Re: PC98 core

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puu
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Re: PC98 core

Unread post by puu »

Thank you.
I tried tracing with the 98DO BIOS, but I used the OUTSB instruction at a very early stage in the BIOS, which seems to be an instruction added after 80186/80286 / V30, but in Zet this is executed Unable, exception 06: It seems that an undefined instruction has occurred. (I think exception 06 was reserved on 8086) It doesn't seem to work as it is.
However, it is predicted that it will not be so difficult to modify Zet (CPU core) to support OUTSB instructions, so I am thinking about proceeding with this method.
Mosojol
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Re: PC98 core

Unread post by Mosojol »

I'm thinking you could maybe make a 8086 that supports some of the 286+ instructions not related to protected mode? It would certainly allow a larger variety of programs to run too (programs compiled for 286+ that don't use its features but compiler optimizations make them use those instructions).
Is GDC working? Is there possibility of GRCG (not EGC) features?
puu
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Re: PC98 core

Unread post by puu »

This is the progress at the moment:
The INS and OUTS instructions that are missing in the 80286's real mode base have been added, and it seems that the INS instruction is not used in the BIOS, so it has been confirmed that the OUTS instruction works normally. The PUSHA and POPA instructions were implemented, but we found a bug and fixed it. As a result, the microcode has been expanded from 9-bit addresses to 10-bit addresses, so it is possible to increase the number of instructions to just under twice.
In GDC, the dot, line, and square drawing circuits are working for the time being. Circles and arcs have not been implemented yet. GRCG is also implemented.
Since I haven't connected the FDC yet, I can only boot ROM BASIC, but it is at the stage where ROM BASIC can be booted. Therefore, I think that development will proceed because the IO port can be accessed freely.

By the way, the development environment is DE0-CV. I will not port it to MiSTer until it is a little more complete.
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