Added stage 1 bootloader

bootloader/bios/print.asm

@@ -0,0 +1,67 @@
+SECTION .text
+USE16
+
+; provide function for printing in x86 real mode
+
+; print a string and a newline
+; CLOBBER
+;   ax
+print_line:
+    mov al, 13
+    call print_char
+    mov al, 10
+    jmp print_char
+
+; print a string
+; IN
+;   si: points at zero-terminated String
+; CLOBBER
+;   si, ax
+print:
+    pushf
+    cld
+.loop:
+    lodsb
+    test al, al
+    jz .done
+    call print_char
+    jmp .loop
+.done:
+    popf
+    ret
+
+; print a character
+; IN
+;   al: character to print
+print_char:
+    pusha
+    mov bx, 7
+    mov ah, 0x0e
+    int 0x10
+    popa
+    ret
+
+; print a number in hex
+; IN
+;   bx: the number
+; CLOBBER
+;   al, cx
+print_hex:
+    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