100 lines
2.8 KiB
ArmAsm
100 lines
2.8 KiB
ArmAsm
; This is the minimal startup & I/O needed to run a basic RETRO
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; instance on x86 hardware.
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; =============================================================
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MODULEALIGN equ 1<<0
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MEMINFO equ 1<<1
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FLAGS equ MODULEALIGN | MEMINFO
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MAGIC equ 0x1BADB002
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CHECKSUM equ -(MAGIC + FLAGS)
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section .mbheader
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align 4
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MultiBootHeader:
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dd MAGIC
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dd FLAGS
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dd CHECKSUM
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section .data
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gdt:
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dw (.end-.dummy)
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dd .dummy
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dw 0
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.dummy: dw 0,0,0,0
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dw 0xffff,0x0000
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db 0x00,0x9a,0xcf,0x00
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dw 0xffff,0x0000
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db 0x00,0x92,0xcf,0x00
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.end:
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section .text
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extern main
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global loader
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global _start
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global getchar
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STACKSIZE equ 0x4000
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align 4
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loader:
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_start:
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lgdt [gdt]
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mov esp, stack+STACKSIZE
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push dword 0
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push dword 0
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jmp main
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jmp $
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align 4
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getchar:
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xor eax, eax ; clear eax
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.a: in al, 64h ; Is any data waiting?
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test al, 1 ; Is character = ASCII 0?
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jz .a ; Yes? Try again
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in al, 60h ; Otherwise, read scancode
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xor edx, edx ; edx: 0=make, 1=break
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test al, 80h ; Is character = HEX 80h?
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jz .b ; Skip the next line
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inc edx ; Update edx
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.b: and al, 7Fh ; Filters to handle
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cmp al, 39h ; the ignored keys
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ja .a ; We just try another key
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mov ecx, [board] ; Load the keymap
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mov al, [ecx+eax] ; Get the key ASCII char
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or al, al ; Is is = 0?
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js .shift ; No, use CAPITALS
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jz .a ; Ignore 0's
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or dl, dl ; Filter for break code
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jnz .a ; Ignore break code
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jmp .done ; Skip to end
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.shift: mov ecx, [edx*4 + .shifts] ; Load the CAPITAL keymap
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mov [board], ecx ; Store into BOARD pointer
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jmp .a ; And try again
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.done: ret
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section .data
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.shifts dd shift, alpha
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board dd alpha
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alpha:
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db 0,27,"1234567890-=",8 ;00-0E
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db 9,"qwertyuiop[]",10 ;0F-1C
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db 0,"asdfghjkl;'`" ;1D-29
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db -1,"\zxcvbnm,./",-1,"*",0,32,-2 ;2A-3A
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shift:
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db 0,27,"!@#$%^&*()_+",8 ;00-0E
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db 9,"QWERTYUIOP{}",10 ;0F-1C
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db 0,'ASDFGHJKL:"~' ;1D-29
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db -1,"|ZXCVBNM<>?",-1,"*",0,32,-2 ;2A-3A
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section .bss
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align 4
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stack:
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resb STACKSIZE
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stack_ptr:
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