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lessons 8, 9, 10, entering 32-bit mode

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Carlos Fenollosa 2014-10-09 11:41:23 +02:00
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08-32bit-print/README.md
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**Goal: Print on the screen when on 32-bit protected mode** **Goal: Print on the screen when on 32-bit protected mode**
32-bit mode allows us to use 32 bit registers and memory addressing, 32-bit mode allows us to use 32 bit registers and memory addressing,
protected memory, virtual memory and other advangades, but we will lose protected memory, virtual memory and other advantages, but we will lose
BIOS interrupts and we'll need to code the GDT (more on this later) BIOS interrupts and we'll need to code the GDT (more on this later)
In this lesson we will write a print string routine by directly manipulating In this lesson we will write a new print string routine which works in
32-bit mode, where we don't have BIOS interrupts, by directly manipulating
the VGA video memory instead of calling `int 0x10`. The VGA memory starts the VGA video memory instead of calling `int 0x10`. The VGA memory starts
at address `0xb8000` and it has a text mode which is useful to avoid at address `0xb8000` and it has a text mode which is useful to avoid
manipulating direct pixels. manipulating direct pixels.
The formula for accessing a specific character on the 80x25 grid is: The formula for accessing a specific character on the 80x25 grid is:
`0xb8000 + 2 * (row * 80 + col)` `0xb8000 + 2 * (row * 80 + col)`