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fixing bootloader again but should work using nasm now

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Gregory Kenneth Bowne
2025-08-06 01:42:17 -07:00
parent 16309bc306
commit dd68fd805f
2 changed files with 41 additions and 15 deletions
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23
bootloader/boot.asm
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@@ -119,20 +119,27 @@ verify_checksum:
lba_to_chs:
pusha
xor dx, dx
mov bx, [sectors_per_track]
div bx ; AX = LBA / sectors_per_track, DX = LBA % spt
mov si, ax ; temp quotient
div bx ; AX = LBA / sectors_per_track, DX = remainder (sector number)
mov si, ax ; SI = temp quotient (track index)
mov cx, [heads_per_cylinder]
xor dx, dx
div cx ; AX = cylinder, DX = head
mov ch, al ; CH = cylinder low
mov ch, al ; CH = cylinder low byte
mov dh, dl ; DH = head
mov cl, sil ; CL = sector number (0-based)
inc cl ; Sector is 1-based
mov ah, al
and ah, 0xC0 ; upper 2 bits of cylinder
or cl, ah ; insert upper cylinder bits into CL
; Now take sector number from earlier remainder
mov cx, si ; Copy track index to CX to access CL
and cl, 0x3F ; Mask to 6 bits (sector number)
inc cl ; Sector numbers are 1-based
; Insert upper 2 bits of cylinder into CL
mov ah, al ; AH = cylinder again
and ah, 0xC0 ; Get top 2 bits of cylinder
or cl, ah ; OR them into sector byte
popa
ret