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comment on flushing predecode queue (pre-Pentium) (DOSX)

posted by Ninho E-mail, 23.04.2008, 23:32

> No. Pentium and above will always "serialize" certain opcodes, including
> moves to control registers.
Anyway, what I wrote is I'm not sure if Intel retired their prescription of a short jump after mode change, in the general architecture manuals, regardless of if it's needed on a particular processor.

> > I'm really surprised you are not aware of this point, considering the
> > depth of your experience.
>
> I AM aware of this, indeed, I had some rather longish discussions with
> someone calling himself Eric (Auer) about this topic. Amazing how one can
> waste time about a piece of code approc. 6 lines long ... :-D
Don't worry, I'm too old to waste time on something like that, and I won't be using the driver anyway. I sure would recompile it with the jmp short if I were to use it and even more compellingly, if my seal were put on it, because that would be the right thing to do : it is prescribed on certain processors, and it will cost virtually nothing where it isn't (modern processors will 'execute' the jmp $+2 in zero time, hidden in the pipeline.)

OK, my 386 Mobo is dead but I'll try himemx on one of my 486 DXs in a few days, I'm sure it works since you checked it, but it may have been only by chance (instruction length, code alignment, cache refill. The 486 is very sensitive to code alignment within 16-byte boundaries). A future compile might change that, exposing the bug, assuming it is one.

Later...

---
Ninho

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