Add print function with some examples

diff --git a/boot.s b/boot.s
index 76880b009eded1d15e93792478061d121a920859..eb115d0324dd6a2e8e83d94aee9d197d71299392 100644 (file)
--- a/boot.s
+++ b/boot.s
@@ -1,17 +1,22 @@
        bits 16 ; boot sectors run in real mode
        org 7c00h ; boot sector is loaded at 0x7c00
 
+       mov di, printing_numbers
+       call print
+
        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
 
+       mov di, goodbye
+       call print
+
        jmp $
 
+printing_numbers: db "Printing some random hex numbers", 0
+goodbye: db "Thank you for your attention", 0
+
 %include "print.s"
 
        times 510-($-$$) db 0 ; fill with 0 until 0x1fc is reached

diff --git a/print.s b/print.s
index ab6eef4c92c9a66441c0abd6c1999ddc61af5bd3..e1d9bc69d4e1d0cd4341b11213b6ccb8b130d087 100644 (file)
--- a/print.s
+++ b/print.s
@@ -1,12 +1,36 @@
 %define CURRENT_ADDR cs:di
 
+; Prints a null terminated string of your choice.
+; Arguments:
+;     CS:DI - pointer to the string you want to print
+print:
+       pusha
+       mov ah, 0Eh ; teletype print
+.write2:
+       mov al, [CURRENT_ADDR] ; get current char and put it in al
+       cmp al, 0 ; check if al is null (string terminator)
+       je .done ; if it is, start a new line
+       int 10h ; otherwise write the char
+       inc di ; increment pointer to string
+       jmp .write2 ; jump back to this section
+.done:
+       mov al, 0Dh ; carriage return
+       int 10h
+       mov al, 0Ah ; line feed
+       int 10h
+       popa
+       ret ; return
+
+; Prints a word (16-bit value) in hex format.
+; Arguments:
+;     DX - word to print
 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
+       dec di ; decrement string pointer
        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
@@ -20,24 +44,10 @@ print_word:
        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
+       mov di, HEX_OUT
+       call print ; write string
        popa
-       ret ; return
+       ret
 
 .compare:
        cmp al, 0 ; compare al with 0
@@ -118,4 +128,4 @@ print_word:
        mov byte [CURRENT_ADDR], 'F'
        ret
 
-HEX_OUT: db "0x0000"
+HEX_OUT: db "0x0000", 0