Bootable kernel skeleton

bootloader/x86/print16.asm

@@ -0,0 +1,66 @@
+SECTION .text
+USE16
+; provide function for printing in x86 real mode
+
+
+; a newline
+newline: db 0xD, 0xA, 0
+
+; print a string and a newline
+; IN
+;   si: points at zero-terminated String
+; CLOBBER
+;   ax
+print_line:
+    mov si, newline
+    call print
+    ret
+
+; print a string
+; IN
+;   si: points at zero-terminated String
+; CLOBBER
+;   ax
+print:
+    lodsb
+    test al, al
+    jz .done
+    call print_char
+    jmp print
+.done:
+    ret
+
+; print a character
+; IN
+;   al: character to print
+; CLOBBER
+;   ah
+print_char:
+    mov ah, 0x0e
+    int 0x10
+    ret
+
+; print a number in hex
+; IN
+;   bx: the number
+; CLOBBER
+;   cx, ax
+print_num:
+    mov cx, 4
+.lp:
+    mov al, bh
+    shr al, 4
+
+    cmp al, 0xA
+    jb .below_0xA
+
+    add al, 'A' - 0xA - '0'
+.below_0xA:
+    add al, '0'
+
+    call print_char
+
+    shl bx, 4
+    loop .lp
+
+    ret