real mode programming

ezome · Post by **ezome** » Mon Sep 03, 2007 8:46 am

does anyone know a good reference about register behavior/usage in real mode

i wrote a bootloader and it seems to work fine but my c kernel acts a little bit strange and i dont know if maybe i messed it up from real mode

JamesM · Post by **JamesM** » Mon Sep 03, 2007 8:57 am

AFAIK register behaviour shouldn't change from real->protected mode, as register's are static and dont have any set 'behaviour'... ?

Not quite sure what you're asking

ezome · Post by **ezome** » Mon Sep 03, 2007 9:10 am

i'm just not sure how the different registers are used and how i could mess up my memory without noticing

the only register i ever initialize is sp and i'm not even sure how registers are changed by a call

so all i would need is a detailed reference how commands effect registers and so on

neon · Post by **neon** » Mon Sep 03, 2007 9:12 am

I *think* he's referring to memory addressing with the segment registers, which does change between real/pmode's.

If so, then its just the standard seg:offset model under real mode... As long as you stay real mode, they cannot change behavior.

I suspect there is probably a different problem with your code.

AJ · Post by AJ » Mon Sep 03, 2007 9:14 am

Hi,

Although there can be an art to choosing the correct register for the correct thing, if you are programming in real mode in assembly, you can pretty much do what you like.

Have a look at this reference: http://www.swansontec.com/sregisters.html which I found quite interesting reading.

Cheers,
Adam

ezome · Post by **ezome** » Mon Sep 03, 2007 11:27 am

neon wrote:I *think* he's referring to memory addressing with the segment registers, which does change between real/pmode's.

If so, then its just the standard seg:offset model under real mode... As long as you stay real mode, they cannot change behavior.

I suspect there is probably a different problem with your code.

i'm not referring to something specific
i wrote about 5 pages of assembly code for my bootloader and want to get a better understanding just to be sure i did it correctly.

i mean it's working but that doesn't mean there are no errors right?

ezome · Post by **ezome** » Mon Sep 03, 2007 1:57 pm

AJ wrote: Have a look at this reference: http://www.swansontec.com/sregisters.html which I found quite interesting reading.

thanks adam
great article

do u know a good x86 reference which explains
the purpose and how to use each command properly

i'm sometimes quite lost when i dont know which command
i need or how to use it and what it does exactly

Zenith · Post by **Zenith** » Mon Sep 03, 2007 2:14 pm

The Intel Manuals are your friends...

If you're trying to be backwards compatible (like programming in realmode...), use this older manual for the 80386.