OSDev.org

Hi,

As you've obviously got suitable answers from other people I'm going to ignore the last two questions that I didn't get time to answer earlier and focus on the text you linked to.

Example: 1000:1f00 = 10001f00

Unfortunately this isn't correct. Firstly, segment-offset pairs [of this kind] only exist in real mode and you're in pmode. Secondly, a linear address is calculated from a segment:offset pair by shifting the segment selector 4 bits left and adding the offset, giving you 20 bits (1MB) of addressable space (16+4 = 20).

To get a 20 bit address, you take the 32 bit, shift the bits to left, until the “12” last bits are “0”.

That's incorrect too - To get the 20-bit page directory/table index you logically shift a 32-bit address RIGHT by 12 bits, so that the most significant 12 bits are zero. It's important that it's a logical shift and not an algebraic one as the latter will implicitly sign extend for you. In C, avoid this by ensuring you use unsigned values.

6 bit: set this to “1” to make the page usable.

That's incorrect - you don't need to set bit 6. Unfortunately I'm at my girlfriend's house at the moment and don't have a PDF reader to look it up in the manuals to see what that bit exactly is, but it definately is not required to be set.

2 bit: if this is set to “1”, then the user level is “supervisor” if the bit is ”0”, then it is normal user.

The inverse - Set for user-mode access, clear for kernel only.

Your tutorial seems to be lacking any information about actually using the stuff in practice - the "last part", as you put it.

As English is clearly not your native language I decided to avoid my usual pedantic language and ambiguity analysis

Anyway, I hope this helped a little.

Cheers,

James

You are right about, that english is not my native language, but as long as people understand me....
well, it helped much.
About the 6 bit, in the "diagram" it is said: "availble"; does that not mean that it can be used, if is not set ?
But what would you like to add to the "last part" ? (about the last part: an example code, i need to make one working, and since i dont have one...)


Kmtdk