1 files changed, 43 insertions, 0 deletions
diff --git a/kernel/drivers/uart.c b/kernel/drivers/uart.c
new file mode 100644
index 0000000..c999e45
--- /dev/null
+++ b/kernel/drivers/uart.c
@@ -0,0 +1,43 @@
+#include <comus/drivers/uart.h>
+#include <comus/asm.h>
+
+#define PORT 0x3F8
+
+int uart_init(void) {
+	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); // ???
+	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 uart_in(void) {
+	// wait for data to be available
+	while ((inb(PORT + 5) & 0x01) == 0);
+	return inb(PORT);
+}
+
+void uart_out(uint8_t ch) {
+	// wait for output to be free
+	while ((inb(PORT + 5) & 0x20) == 0);
+	outb(PORT, ch);
+}
+
+void uart_out_str(const char *str) {
+	while (*str)
+		uart_out(*str++);
+}