From f9f4f8ebffb463d53ae5a239ddfbe8380f258b8b Mon Sep 17 00:00:00 2001 From: =?utf8?q?Duje=20Mihanovi=C4=87?= Date: Sat, 21 Aug 2021 12:00:08 +0200 Subject: [PATCH] Can now print hexadecimal numbers --- boot.s | 32 +++++++-------- print.s | 121 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 2 files changed, 135 insertions(+), 18 deletions(-) create mode 100644 print.s diff --git a/boot.s b/boot.s index 50730d0..76880b0 100644 --- a/boot.s +++ b/boot.s @@ -1,22 +1,18 @@ bits 16 ; boot sectors run in real mode - org 7c00h ; boot sector is always loaded at 0x7c00 + org 7c00h ; boot sector is loaded at 0x7c00 - mov al, 1 ; update cursor after write - mov bh, 0 ; write to page 0 - mov bl, 00000111b ; attribute: high nibble is foreground (light gray), - ; low nibble is background (black) - ; NOTE: in the binary, these will be inverted, so low nibble here will become high nibble in binary and vice versa! - mov cx, msg1end - msg1 ; size of message - mov dl, 0 ; column to write to - mov dh, 0 ; row to write to - push cs ; push code segment to stack - pop es ; pop pushed code segment to extra segment, this serves as the base to the string - mov bp, msg1 ; offset where the string is - mov ah, 13h ; write string subservice - int 10h ; call BIOS interrupt 0x10 - jmp msg1end ; jmp to endless loop - msg1 db "Gotta start somewhere" - msg1end: jmp msg1end + mov dx, 0DEADh ; number to print + mov cl, 0 ; column + mov ch, 0 ; row + call print_word + mov dx, 0BEEFh + mov cl, 0 + mov ch, 1 + call print_word + + jmp $ + +%include "print.s" times 510-($-$$) db 0 ; fill with 0 until 0x1fc is reached - dw 0xaa55 ; BIOS MBR signature + dw 0AA55h ; BIOS MBR signature diff --git a/print.s b/print.s new file mode 100644 index 0000000..ab6eef4 --- /dev/null +++ b/print.s @@ -0,0 +1,121 @@ +%define CURRENT_ADDR cs:di + +print_word: + pusha ; push all regs to stack + mov di, HEX_OUT+5 ; set destination index to last char in HEX_OUT + mov ax, dx ; copy argument to accumulator + and al, 00001111b ; extract the low nibble of the low half of the accumulator + call .compare ; fill in the string with correct value + dec di ; decrement destination index + mov ax, dx ; copy argument to accumulator + and al, 11110000b ; extract high nibble of low half of accumulator + shr al, 4 ; shift high nibble to low nibble + call .compare ; fill in string with correct value + dec di + mov al, ah ; copy high portion of accumulator to low + and al, 00001111b ; + call .compare + dec di + mov al, ah + and al, 11110000b + shr al, 4 + call .compare + jmp .write ; write string + +.write: + popa ; get back our arguments + mov dl, cl ; column + mov dh, ch ; row + pusha ; save registers + mov al, 1 ; update cursor + mov bh, 0 ; page number + mov bl, 00000111b ; colors + mov cx, 6 ; length of string + push cs ; push code segment address + pop es ; pop to extra segment address + mov bp, HEX_OUT ; offset to extra segment of string + mov ah, 13h ; write string + int 10h ; BIOS interrupt + popa + ret ; return + +.compare: + cmp al, 0 ; compare al with 0 + jne .one ; if not equal, compare with 1 + mov byte [CURRENT_ADDR], '0' ; set character to ASCII 0 + ret ; return +.one: + cmp al, 1 + jne .two + mov byte [CURRENT_ADDR], '1' + ret +.two: + cmp al, 2 + jne .three + mov byte [CURRENT_ADDR], '2' + ret +.three: + cmp al, 3 + jne .four + mov byte [CURRENT_ADDR], '3' + ret +.four: + cmp al, 4 + jne .five + mov byte [CURRENT_ADDR], '4' + ret +.five: + cmp al, 5 + jne .six + mov byte [CURRENT_ADDR], '5' + ret +.six: + cmp al, 6 + jne .seven + mov byte [CURRENT_ADDR], '6' + ret +.seven: + cmp al, 7 + jne .eight + mov byte [CURRENT_ADDR], '7' + ret +.eight: + cmp al, 8 + jne .nine + mov byte [CURRENT_ADDR], '8' + ret +.nine: + cmp al, 9 + jne .ten + mov byte [CURRENT_ADDR], '9' + ret +.ten: + cmp al, 0Ah + jne .eleven + mov byte [CURRENT_ADDR], 'A' + ret +.eleven: + cmp al, 0Bh + jne .twelve + mov byte [CURRENT_ADDR], 'B' + ret +.twelve: + cmp al, 0Ch + jne .thirteen + mov byte [CURRENT_ADDR], 'C' + ret +.thirteen: + cmp al, 0Dh + jne .fourteen + mov byte [CURRENT_ADDR], 'D' + ret +.fourteen: + cmp al, 0Eh + jne .fifteen + mov byte [CURRENT_ADDR], 'E' + ret +.fifteen: + mov byte [CURRENT_ADDR], 'F' + ret + +HEX_OUT: db "0x0000" -- 2.39.5