From: Duje Mihanović <duje.mihanovic@skole.hr>
Date: Sat, 21 Aug 2021 10:00:08 +0000 (+0200)
Subject: Can now print hexadecimal numbers
X-Git-Tag: 0.1.0~30
X-Git-Url: http://git.dujemihanovic.xyz/posts?a=commitdiff_plain;h=f9f4f8ebffb463d53ae5a239ddfbe8380f258b8b;p=nameless-os.git

Can now print hexadecimal numbers
---

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"