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DOSBox-X 0.84.2 / 2022.08.0 released! (Announce)

posted by tkchia Homepage, 11.01.2023, 21:53

Hello Japheth, hello ecm, hello bretjohn,

> No, Candyman is not confused. He talks about "32-bit real-mode", that is,
> the cpu is switched to protected-mode, CS is loaded with a "32-bit"
> selector ( D-bit = 1 ), and then the cpu is switched back to real-mode (
> with the D bit in CS attr still set ).
I see Michal Necasek has this to say about this mode (https://www.os2museum.com/wp/a-brief-history-of-unreal-mode/):

> It is also possible to set the D bit in CS [for unreal mode], changing the default operand size to 32-bit. This may reduce the size of unreal code if it is largely 32-bit (by obviating the need for overrides). Unfortunately, this again causes serious trouble with interrupts, because existing 16-bit code cannot run correctly with the D bit set. It is possible to switch to protected mode, clear the D bit, and execute the 16-bit handler every time an interrupt occurs, and in fact it’s exactly what fasm does (or at least did in some versions), but with so much mode switching and complexity, the advantages of unreal mode are rapidly lost. ...
> A larger problem is that the "advanced" aspects of unreal mode may not be implemented identically across CPU generations and vendors, precisely because they have never been documented. ... Protected mode, on the other hand, works consistently.
Thank you!

---
https://gitlab.com/tkchia · https://codeberg.org/tkchia · 😴 "MOV AX,0D500H+CMOS_REG_D+NMI"

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