Can now print hexadecimal numbers

diff --git a/boot.s b/boot.s
index 50730d0c39dd9566f3eef2e0b87582758af13444..76880b009eded1d15e93792478061d121a920859 100644 (file)
--- 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 (file)
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"