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88 lines
1.8 KiB
ArmAsm
88 lines
1.8 KiB
ArmAsm
; BIOS puts our boot sector at 0000:7c00
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org 0x7c00
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; We're (probably) in real mode
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bits 16
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; Disable interrupts, fuck knows what an interrupt would do right now
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cli
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xor ax, ax
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mov ds, ax
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mov es, ax
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; Put the stack base at the address of our program text (stack will grow high->low away from it).
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; We're not doing anything with a stack right now but who knows we might want to later
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mov ss, ax
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mov sp, 0x7c00
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; Segment for VGA (0xb800 * 16 = 0xb8000)
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mov ax, 0xb800
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mov fs, ax
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; Set VGA mode
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; https://mendelson.org/wpdos/videomodes.txt
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mov ah, 0x00
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mov al, 0x03
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int 0x10
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; Reveal the true nature of jen
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xor bx, bx
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mov ax, 17
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loop:
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cmp ax, bx
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jle done
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lea si, [womble + bx]
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mov dh, [si]
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mov di, bx
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shl di, 1
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mov byte fs:[di], dh
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mov byte fs:[di + 1], 0x1f
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inc bx
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jmp loop
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done:
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hlt
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womble:
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db "jen is a womble!"
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; TODO: enable A20
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; TODO: load a second stage
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; TODO: grab all the info we can from bios interrupts and deliver it to ths OS nicely
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; e.g. in a fixed memory location
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; TODO:
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; - Generate GPT in justfile
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; - Parse global parition table
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; - Load second stage from GPT partition with a particular UUID / name like GRUB does
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; (it's Hah!IdontNeedEFI in GRUB)
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; - https://en.wikipedia.org/wiki/BIOS_boot_partition
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; - Future work:
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; - Boot from UEFI
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; - Boot on non-GPT partitioned disk
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; MBR bootstrap field is 440 bytes long
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%if ($ - $$) > 440
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%error "exceeded mbr bootstrap field size"
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%endif
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; Pad to the end of the MBR bootstrap field
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times 440 - ($ - $$) db 0
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; Unique disk ID
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dd 0x00000000
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; Reserved
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dw 0x0000
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; Zero the partition fields
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; TODO: fill in the field pointing to the GPT table
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times 510 - ($ - $$) db 0
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; Boot signature
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db 0x55
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db 0xaa
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