StupidOS/kernel/sys/i386/mmu.inc

	;; File: mmu.inc
	;;
	;; About: Address Translation
	;;
	;; Since we don't use segmentation, this is how address translation works
	;; > 31       21       11       0
	;; > +--------+--------+--------+
	;; > |   DIR  |  PAGE  | OFFSET |
	;; > +--------+--------+--------+
	;; >               |
	;; >               v
	;; >         Page Translation
	;; >               |
	;; > 31            v            0
	;; > +--------------------------+
	;; > |     Pyshical address     |
	;; > +--------------------------+
	;;
	;; About: Page Translation
	;;
	;; > +--------+--------+--------+             +--------+
	;; > |   DIR  |  PAGE  | OFFSET |-----+       |  Phys  |
	;; > +--------+--------+--------+     +------>|  addr  |
	;; >   |             |                        |        |
	;; >   |             +----+                   +--------+
	;; >   |   Page Dir       |             +---> Page Frame
	;; >   |  +---------+     |  +--------+ |
	;; >   |  |         |     |  |        | |
	;; >   +->| PDE     |-+   +->| PTE    |-+
	;; >      |         | |      |        |
	;; >      +---------+ |      +--------+
	;; >                  +----> Page Table
	;; >
	;;

	;; Macro: V2P(addr)
	;; Convert Kernel Address to Physical Address
%define V2P(addr)   (addr - KERNBASE)

	;; Macro: P2V(addr)
	;; Convert Physical Address to Kernel Address
%define P2V(addr)   (addr + KERNBASE)

%define P2PDE(addr) ((addr >> 22) & 0x3FF)
%define PDE2P(addr) (addr << 22)
%define P2PTE(addr) ((addr >> 12) & 0x3FF)

	;; Defines: Page Directory Flags
	;; PDE_P   - Present
	;; PDE_W   - Writable
	;; PDE_U   - User
	;; PDE_PWT - Write-Through
	;; PDE_PS  - 4MiB page
PDE_P   equ 1 << 0
PDE_W   equ 1 << 1
PDE_U   equ 1 << 2
PDE_PWT equ 1 << 3
PDE_PCD equ 1 << 4
PDE_A   equ 1 << 5
PDE_D   equ 1 << 6
PDE_PS  equ 1 << 7
PDE_G   equ 1 << 8

	;; Defines: Page Table Flags
	;; PTE_P   - Present
	;; PTE_W   - Writable
	;; PTE_U   - User
	;; PTE_PWT - Write-Through
	;; PTE_PCD - Cache Disable
	;; PTE_A   - Accessed
	;; PTE_D   - Dirty
	;; PTE_PAT - TODO
	;; PTE_G   - TODO
PTE_P   equ 1 << 0
PTE_W   equ 1 << 1
PTE_U   equ 1 << 2
PTE_PWT equ 1 << 3
PTE_PCD equ 1 << 4
PTE_A   equ 1 << 5
PTE_D   equ 1 << 6
PTE_PAT equ 1 << 7
PTE_G   equ 1 << 8

struc gdt_entry
	.limit_low: resw 1
	.base_low:  resw 1
	.base_mid:  resb 1
	.access:    resb 1
	.flags:     resb 1
	.base_high: resb 1
endstruc