serial ports, echo vga output over COM2

src/kernel/serial.asm

@@ -18,12 +18,71 @@
 global send_byte
 global read_byte
 
-section .text
-;COM1:   COM2:   COM3:   COM4:
-;0x03f8, 0x02f8, 0x03e8, 0x02e8
-
 send_byte:;void send_byte(uint8_t value, uint8_t port)
-  ;TODO
+  push ebp
+  mov ebp, esp
+
+  mov cl, byte [ebp + 8] ;value
+  xor edx, edx
+  mov dl, byte [ebp + 12];port
+
+  test dl, 0xfc
+  jnz .leave
+
+  xchg ebx, edx
+  shl bl, 1
+  mov ax, word [ebx + com_ports]
+  mov ebx, edx
+  mov dx, ax
+
+  or dx, 5
+
+.check_ready:
+  in al, dx
+  test al, 0x20
+  jz .check_ready
+
+  and dx, 0xfff8
+
+  mov al, cl
+  out dx, al
+
+.leave:
+  leave
+  ret
 
 read_byte:;uint8_t read_byte(uint8_t port)
-  ;TODO
+  push ebp
+  mov ebp, esp
+
+  xor eax, eax
+
+  xor edx, edx
+  mov dl, byte [ebp + 8];port
+
+  test dl, 0xfc
+  jnz .leave
+
+  xchg ebx, edx
+  shl bl, 1
+  mov cx, word [ebx + com_ports]
+  mov ebx, edx
+  mov dx, cx
+
+  or dx, 5
+
+.check_ready:
+  in al, dx
+  test al, 0x01
+  jz .check_ready
+
+  and dx, 0xfff8
+
+  in al, dx
+
+.leave:
+  leave
+  ret
+
+section .rodata
+com_ports dw 0x03f8, 0x02f8, 0x03e8, 0x02e8

src/kernel/serial.h

@@ -29,10 +29,7 @@ enum serials {
   COM4 = 3
 };
 
-/*
-Commenting out so I don't accidentally call garbage while these are unimplemented.
 void send_byte(uint8_t value, uint8_t port);
 uint8_t read_byte(uint8_t port);
-*/
 
 #endif

src/kernel/vga.c

@@ -43,7 +43,7 @@ void scroll(void) {
 }
 
 void put_char(uint8_t ch) {
-  //send_byte(ch, COM2);
+  send_byte(ch, COM2);
   switch (ch) {
   case '\b':
     if (cursor_pos)