serial and fix makefile

Makefile

@@ -31,10 +31,6 @@ $(A_OBJ): $(BUILD_DIR)/%.S.o : %.S
 	@mkdir -p $(@D)
 	nasm $< -f elf64 -o $@
 
-$(BUILD_DIR)/$(SRC_DIR)/arch/amd64/shim.o: $(SRC_DIR)/arch/amd64/shim.c
-	@mkdir -p $(@D)
-	$(CC) -c $(CFLAGS) -o $@ $< -m32
-
 $(C_OBJ): $(BUILD_DIR)/%.o : %.c
 	@mkdir -p $(@D)
 	$(CC) -c $(CFLAGS) -o $@ $<

include/serial.h

@@ -0,0 +1,15 @@
+#pragma once
+
+#include <stdint.h>
+
+enum serial_com_port {
+	COM1 = 1,
+	COM2 = 2,
+	COM3 = 3,
+	COM4 = 4,
+};
+
+int serial_init(enum serial_com_port com);
+uint8_t serial_in(enum serial_com_port com);
+void serial_out(enum serial_com_port com, uint8_t ch);
+void serial_out_str(enum serial_com_port com, char *str);

src/arch/amd64/serial.c

@@ -0,0 +1,58 @@
+#include <serial.h>
+#include "bindings.h"
+
+// port numbers for first four serial ports
+static uint16_t SERIAL_PORTS[] = { 
+	[COM1] = 0x3F8, 
+	[COM2] = 0x2F8, 
+	[COM3] = 0x3E8, 
+	[COM4] = 0x2E8,
+};
+
+// initialize the specified COM port for serial
+// see https://wiki.osdev.org/Serial_Ports
+// and https://en.wikibooks.org/wiki/Serial_Programming/8250_UART_Programming
+int serial_init(enum serial_com_port com) {
+	uint16_t port = SERIAL_PORTS[com];
+	outb(port + 1, 0x00); // disable interrupts
+	outb(port + 3, 0x80); // enable DLAB (divisor latch access bit)
+	outb(port + 0, 0x03); // (lo) Set baud divisor to 3 38400 baud
+	outb(port + 1, 0x00); // (hi)
+	outb(port + 3, 0x03); // disable DLAB, set 8 bits per word, one stop bit, no parity
+	outb(port + 2, 0xC7); // enable and clear FIFOs, set to maximum threshold
+	// outb(port + 4, 0x0B); // TODO copied this from osdev wiki but i don't think you need it here
+	outb(port + 4, 0x1E); // set in loopback mode for test
+	outb(port + 0, 0xAE); // test by sending 0xAE
+	
+	uint8_t response = inb(port + 0);
+	if(response != 0xAE) {
+		// TODO panic here?
+		return -1;
+	}
+
+	// disable loopback, enable IRQs
+	outb(port + 4, 0x0F);
+	return 0;
+}
+
+uint8_t serial_in(enum serial_com_port com) {
+	uint16_t port = SERIAL_PORTS[com];
+	// wait for data to be available
+	while((inb(port + 5) & 0x01) == 0);
+	return inb(port);
+}
+
+void serial_out(enum serial_com_port com, uint8_t ch) {
+	uint16_t port = SERIAL_PORTS[com];
+	// wait for output to be free
+	while((inb(port + 5) & 0x20) == 0);
+	outb(port, ch);
+}
+
+void serial_out_str(enum serial_com_port com, char *str) {
+	uint16_t port = SERIAL_PORTS[com];
+	for(; *str != '\0'; str++) {
+		while((inb(port + 5) & 0x20) == 0);
+		outb(port, *str);
+	}
+}