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Listen to BIOS for drive number

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Boots on my laptop now!
This commit is contained in:
Robbe Van Herck 2020-01-03 11:21:13 +01:00
parent 7b91b68403
commit 3689c55b45
No known key found for this signature in database
GPG key ID: A66F76F7B81BD784
2 changed files with 16 additions and 18 deletions
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28
bootloader/main.asm
View file

@ -1,4 +1,4 @@
DISK_ID EQU 0x80 ; DISK_ID EQU 0x80
KERNEL_START EQU 0x100000 KERNEL_START EQU 0x100000
ELF_START EQU 0x8000 ELF_START EQU 0x8000
@ -73,14 +73,14 @@ ret
puthex: puthex:
; Print high bits ; Print high bits
mov dl, bl mov cl, bl
shr dl, 4 shr cl, 4
cmp dl, 9 cmp cl, 9
jg .puthex_high_alpha jg .puthex_high_alpha
; It's < 10, print as digit ; It's < 10, print as digit
mov al, dl mov al, cl
add al, 0x30 add al, 0x30
mov ah, 0x0e mov ah, 0x0e
int 0x10 int 0x10
@ -88,21 +88,21 @@ jmp .puthex_low
.puthex_high_alpha: .puthex_high_alpha:
; It's >= 10, print as letter ; It's >= 10, print as letter
mov al, dl mov al, cl
add al, 0x57 ; 0x57 = (0x61 - 10) add al, 0x57 ; 0x57 = (0x61 - 10)
mov ah, 0x0e mov ah, 0x0e
int 0x10 int 0x10
.puthex_low: .puthex_low:
; Print low bits ; Print low bits
mov dl, bl mov cl, bl
and dl, 0b1111 and cl, 0b1111
cmp dl, 9 cmp cl, 9
jg .puthex_low_alpha jg .puthex_low_alpha
; It's < 10, print as digit ; It's < 10, print as digit
mov al, dl mov al, cl
add al, 0x30 add al, 0x30
mov ah, 0x0e mov ah, 0x0e
int 0x10 int 0x10
@ -110,7 +110,7 @@ jmp .puthex_end
.puthex_low_alpha: .puthex_low_alpha:
; It's >= 10, print as letter ; It's >= 10, print as letter
mov al, dl mov al, cl
add al, 0x57 ; 0x57 = (0x61 - 10) add al, 0x57 ; 0x57 = (0x61 - 10)
mov ah, 0x0e mov ah, 0x0e
int 0x10 int 0x10
@ -136,10 +136,12 @@ mov ch, 0b00100000
mov cl, 0b00000000 mov cl, 0b00000000
int 0x10 int 0x10
mov bl, dl
call puthex
; reset disk system ; reset disk system
mov ah, 0x00 mov ah, 0x00
mov dl, DISK_ID ; mov dl, DISK_ID
int 0x13 int 0x13
; print result on error ; print result on error
@ -158,7 +160,7 @@ mov al, 0x01 ; number of sectors
mov ch, 0x00 ; cylinder number, low 8 bits mov ch, 0x00 ; cylinder number, low 8 bits
; mov cl, 0x01 ; cylinder number, high 2 bits + sector number (6 bits) ; mov cl, 0x01 ; cylinder number, high 2 bits + sector number (6 bits)
mov dh, 0x00 ; head number mov dh, 0x00 ; head number
mov dl, DISK_ID ; drive number ; mov dl, DISK_ID ; drive number
int 0x13 int 0x13
; exit on error ; exit on error

6
docs/bootloader.md
View file

@ -20,10 +20,6 @@ The first 512 bytes are the bootloader, right after that the 32-bit kernel ELF-f
## Known issues ## Known issues
### USB Boot
It doesn't boot the kernel from USB, as BIOS does not recognize USB as valid hard drive for int 13, only hard drives and floppies. Thus it loads sectors 2-65 from the hard drive. If this is written on a hard drive, it could work if DRIVE_ID is set correctly.
### Stack setup ### Stack setup
As I don't quite get how segments work in real mode, there are most likely errors in the way I set up my stack. I'm going on a _it works on my qemu_ approach currently. As I don't quite get how segments work in real mode, there are most likely errors in the way I set up my stack. I'm going on a _it works on my machine_ approach currently.