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;Copyright 2019 Benji Dial
;Permission to use, copy, modify, and/or distribute this
;software for any purpose with or without fee is hereby
;granted, provided that the above copyright notice and this
;permission notice appear in all copies.
;THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS
;ALL WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL
;IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO
;EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
;INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
;WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS,
;WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER
;TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE
;USE OR PERFORMANCE OF THIS SOFTWARE.
pointers:
.fat equ 0x0500
fat_header:
.oem_name equ 0x7c03;mkfs.fat - ignored
.bytes_per_sector equ 0x7c0b;0x0200 - assumed
.sectors_per_cluster equ 0x7c0d;0x01 - assumed
.reserved_sectors equ 0x7c0e;0x0002 - other values handled
.n_fats equ 0x7c10;0x01 - assumed
.directory_entries equ 0x7c11; -
.n_sectors equ 0x7c13;0x0b40 -
.media_type equ 0x7c15; -
.sectors_per_fat equ 0x7c16; - handled
.sectors_per_track equ 0x7c18;0x0012 -
.sides equ 0x7c1a;0x0002 -
.hidden_sectors equ 0x7c1c;0x0000_0000 - assumed
.long_sectors equ 0x7c20;0x0000_0000 - assumed
.drive_number equ 0x7c24; - ignored, used as scratch
.flags equ 0x7c25; - ignored
.signature equ 0x7c26;0x29 - halts on other values
.id equ 0x7c27; - ignored
.label equ 0x7c2b;PORTLAND OS - assumed
.fs_type equ 0x7c36;FAT12 - assumed
org 0x7c3e
bits 16
in al, 0x92
or al, 0x02
out 0x92, al
mov ah, 0x42
mov si, dap
int 0x13
mov byte [fat_header.drive_number], dl
memory:
mov bx, 0x2010
mov eax, 0x0001_0001
.clear:
mov dword [bx], eax
add bx, 4
test bx, 0x4000
jne .clear
xor ax, ax
mov es, ax
mov si, 0x7000
xor ebx, ebx
.loop:
mov eax, 0x0000_e820
mov ecx, 24
mov edx, 0x534d_4150
int 0x15
jc .done
test cl, 24
jne .not_24
test byte [0x7014], 0x01
jz .loop
.not_24:
test dword [0x7010], 1
jne .loop
test byte [0x7003], 0
jne .loop
test dword [0x7004], 0
jne .loop
test dword [0x700c], 0
je .check_lower
mov dword [0x7008], 0xffff_ffff
.check_lower:
test dword [0x7008], 0
je .loop
mov edx, ebx
mov ebx, dword [0x7000]
mov eax, ebx
add eax, dword [0x7008]
jnc .pagify
mov eax, 0xffff_ffff
.pagify:
dec ebx
shr ebx, 12
inc ebx
shr eax, 12
dec eax
test eax, 0xffff_f000
jz .maxed
mov eax, 0x0000_0fff
.maxed:
inc eax
test eax, ebx
je .next
shl ebx, 1
or ebx, 0x2000
shl eax, 1
add eax, 0x2000
mov ecx, eax
xor ax, ax
.free_loop:
mov word [ebx], ax
add ebx, 2
test ebx, ecx
jne .free_loop
.next:
mov ebx, edx
jmp .loop
.done:
mov dword [0x2000], 0x0002_0002
mov dword [0x2004], 0x0002_0002
mov dword [0x2008], 0x0002_0002
mov dword [0x200c], 0x0002_0002
test byte [fat_header.signature], 0x29
jne halt
mov ax, word [fat_header.sectors_per_fat]
mov word [dap.length], ax
dec ax
shr ax, 3
inc ax
fat_allocate:
mov bx, 0x200e
xor cx, cx
mov dx, 0x2200
.loop:
add bx, 2
test bx, dx
je halt
test word [bx], 0x0000
je .eq
xor cx, cx
jmp .loop
.eq:
inc cx
test cx, ax
jne .loop
dec ax
shl ax, 1
sub bx, ax
mov dx, bx
mov ax, 0x0002
.mark_loop:
mov word [bx], ax
loop .mark_loop
mov bx, dx
and ebx, 0x0000_dfff
shl ebx, 12
mov dword [pointers.fat], ebx
mov dl, byte [fat_header.drive_number]
mov ax, word [fat_header.reserved_sectors]
mov word [dap.start], ax
mov word [dap.offset], bx
shr ebx, 16
and bx, 0xf000
mov word [dap.segment], bx
mov ah, 0x42
mov si, dap
int 0x15
mov ebx, dword [pointers.fat]
;fat loaded - load kernel
cli
lgdt [gdt]
mov eax, cr0
or al, 0x01
mov cr0, eax
jmp 0x08:pmode
gdt:
dw 0x28
dd gdt + 6
dq 0x0000_0000_0000_0000
dq 0x0040_9a00_0000_7fff;0x000000 - 0x007fff
dq 0x0040_9200_0000_7fff
dq 0x00c0_9a00_8000_0ff7;0x008000 - 0xffffff
dq 0x00c0_9200_8000_0ff7
dap:
dw 0x0010
.length dw 0x0001
.offset dw 0x7e00
.segment dw 0x0000
.start dq 1
allocate:
;TODO
ret
halt:
cli
.hlt:
hlt
jmp .hlt
bits 32
pmode:
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