220 lines
2.7 KiB
NASM
220 lines
2.7 KiB
NASM
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; ihex - bootsector that reads intel hex from the keyboard
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%define base (0x10000 - 0x400)
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org base
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; relocate to end of memory
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reloc: ; set up src addr
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xor ax, ax
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mov ds, ax
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mov si, 0x7C00
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; calculate target segment
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mov ax, [0x413]
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mov cl, 6
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shl ax, cl
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sub ax, 0x1000
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mov es, ax
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mov di, base
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; set up dst addr
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mov ss, ax
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mov sp, di
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; relocate
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mov cx, 0x100
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rep movsw
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; set DS
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mov ds, ax
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; jump relocated
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push ds
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mov ax, main
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push ax
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retf
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; AL -> display
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putc: mov ah, 0x0e
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xor bx, bx
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int 0x10
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ret
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; read a line
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read: mov si, line
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.loop: xor ax, ax
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int 0x16
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cmp al, 0x08
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je .bs
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cmp al, 0x0A
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je .cr
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cmp al, 0x0D
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je .cr
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cmp ax, 0x4D00
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je .r
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test al, al
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jz .loop
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cmp al, 0x60
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jc .l01
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sub al, 0x20
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.l01: mov [si], al
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.l02: inc si
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call putc
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jmp .loop
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.r: mov al, [si]
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jmp .l02
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.bs: dec si
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push ax
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call putc
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mov al, 0x20
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call putc
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pop ax
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call putc
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jmp .loop
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.cr: mov cx, line
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xchg cx, si
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sub cx, si
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jmp nl
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; read 2 hex chars from line into al
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; BX is byte number
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getb: add bx, bx
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lea si, [line+1+bx]
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mov ax, [si]
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call .a2b
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xchg ah, al
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call .a2b
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test ax, 0xF0F0
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jnz err
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push cx
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mov cl, 4
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shl al, cl
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shr ax, cl
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pop cx
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.ret: ret
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.err: xor ax, ax
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stc
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ret
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.a2b: sub al, 0x30
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cmp al, 0x10
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jc .ret
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sub al, 7
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ret
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; same like getb, except reads a full word
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getw: push bx
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call getb
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mov dl, al
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pop bx
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inc bx
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call getb
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mov ah, dl
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ret
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nl: mov al, 0x0A
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call putc
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mov al, 0x0D
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jmp putc
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main: mov sp, base ; reset stack
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call read
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cmp byte [line], ':'
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jmp hexcmd
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err: mov cx, si
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sub cx, line
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jz .l01
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cmp cx, 80
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jnc .l01
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mov al, ' '
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.l02: call putc
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loop .l02
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.l01: mov al, '^'
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call putc
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mov al, 7
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call putc
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call nl
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jmp main
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hexcmd: sub cx, 11
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jc err
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shr cx, 1
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xor bx, bx
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call getb
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; line not long enough for size field
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cmp cl, al
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jc err
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; calculate checksum
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add cl, 5
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xor dx, dx
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.loop: push bx
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call getb
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pop bx
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add dl, al
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inc bx
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add dl, al
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loop .loop
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jnz err
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; get record type
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mov bx, 3
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call getb
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cmp al, 0
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je cmd0
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cmp al, 1
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je cmd1
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cmp al, 2
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je cmd2
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cmp al, 3
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je cmd3
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jmp err
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; ihex command 0: data
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cmd0: les di, [addr]
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mov bx, 0
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push bx
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call getb
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pop bx
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mov cx, ax
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add bx, 4
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.loop: push bx
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call getb
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pop bx
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inc bx
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stosb
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loop .loop
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mov [addr], di
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jmp main
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; ihex command 1: eof / exec
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cmd1: push word [exec+2]
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push word [exec]
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push es
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pop ds
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retf
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; ihex command 2: set segment
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cmd2: mov bx, 4
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call getw
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mov [addr], ax
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jmp main
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; ihex command 3: set start address
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cmd3: ; copy CS
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mov bx, 4
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call getw
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mov [exec+2], ax
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; copy IP
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mov bx, 6
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call getw
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mov [exec], ax
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jmp main
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hlt: hlt
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jmp hlt
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addr: dw 0, 0x100
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exec: dw 0, 0x100
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times 510-($-$$) db 0x00
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db 0x55,0xaa
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section .bss
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line: resb 80
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