Print to COM1 port

lboot.S

@@ -11,6 +11,8 @@ _start:     cli
             xor         %ax, %ax
             mov         %ax, %ds
 
+            call        init_com1
+
             mov         $msg_start, %si
             call        print
 
@@ -27,6 +29,20 @@ _start:     cli
 1:          hlt
             jmp         1b
 
+.set        COM1,       0x3F8
+.macro      com1_write  offset=0, byte
+            mov         $COM1+\offset, %dx
+            mov         $\byte, %al
+            outb        %al, %dx
+.endm
+
+init_com1:  com1_write  1, 0x00 // clear interrupts
+            com1_write  3, 0x80 // set DLAB to 1
+            com1_write  0, 0x0C // 9600 baud rate
+            com1_write  1, 0x00
+            com1_write  3, 0x07 // 8 bit data + 1 parity bit
+            ret
+
 enable_a20: // TODO more thorough implementation
             inb         $0x92, %al
             or          $2, %al
@@ -53,9 +69,18 @@ unreal:     push        %ds
 
 print:      xor         %bx, %bx
 
-1:          lodsb
+1:          mov         $COM1+5, %dx
+            inb         %dx, %al
+            test        $0x20, %al
+            jz          1b
+
+            lodsb
             or          %al, %al
             jz          2f
+
+            mov         $COM1, %dx
+            outb        %al, %dx
+
             mov         $0x0E, %ah
             int         $0x10
             jmp         1b