Add beginning basic serial driver

src/kernel/interrupts.cpp

@@ -130,7 +130,7 @@ set_idt_entry(uint8_t i, uint64_t addr, uint16_t selector, uint8_t flags)
 	g_idt_table[i].reserved = 0;
 }
 
-void
+static void
 disable_legacy_pic()
 {
 
@@ -154,6 +154,13 @@ disable_legacy_pic()
 	outb(PIC2+1, 0x02); io_wait();
 }
 
+static void
+enable_serial_interrupts()
+{
+	uint8_t ier = inb(COM1+1);
+	outb(COM1+1, ier | 0x1);
+}
+
 void
 interrupts_init()
 {
@@ -186,6 +193,7 @@ interrupts_init()
 
 	idt_write();
 	disable_legacy_pic();
+	enable_serial_interrupts();
 
 	log::info(logs::interrupt, "Interrupts enabled.");
 }
@@ -288,6 +296,11 @@ irq_handler(registers regs)
 		cons->set_color();
 		break;
 
+	case 4:
+		// TODO: move this to a real serial driver
+		cons->echo();
+		break;
+
 	default:
 		cons->set_color(11);
 		cons->printf("\nReceived IRQ interrupt: %d (vec %d)\n",