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Index > DOS > Bresenham line routine for the linear framebuffer with 8 bpp

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freecrac



Joined: 19 Oct 2011
Posts: 117
Location: Germany Hamburg
freecrac
sid123 wrote:
The problem after initializing multiple cores will be BS BIOS interrupts, which switch to Protected Mode and return back to pure real mode, and you're not in Unreal Mode at all. Sad

Do you know any one of those BIOS interrupts wich switches to the Protected Mode?

I guess this is only a problem with some very rare PCI-cards and the most bios routines of all other x86-PCs do not switch to the Protected Mode (after the power on self test of the Bios is done).

So Micosoft uses the BIG-Realmode in one of their "himem.sys" and a lot of DOS-games of the 90" too. But how can it possible, if the BIOS switch to the Protected Mode and back to the Real Mode while running an application that uses the BIG-Realmode?

I reckon this problem was higher conventionalized as it is and the background for this was only for pushing of the comming Windows 95 OS with a comercial lie that more memory can not be access and it is only a bug of the CPU, if the CPU gives the possibility for to access the address above the first MB with th Big-Realmode. So in the intel documentation of their CPUs they give us the garantee that the descriptor cache will be cleared with switching back to the Real Mode. But we known the Intel x86-CPUs do not clear the descriptors cache contrary to their documentation.

Dirk
Post 25 Mar 2014, 10:31
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edfed



Joined: 20 Feb 2006
Posts: 4240
Location: 2018
edfed
the only answer possible:

test it Smile
Post 25 Mar 2014, 11:02
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sid123



Joined: 30 Jul 2013
Posts: 340
Location: Asia, Singapore
sid123
@freecrac: Found a workaround!
In one of the really old versions of FASM, after switching to big real mode FASM modifies the GPF handler which is caused when the application tries to access an offset greater than 0xFFFF in real mode. The GPF handler simply enables Unreal Mode. Smile
Post 25 Mar 2014, 12:06
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