1 files changed, 118 insertions, 0 deletions

diff --git a/src/serial.rs b/src/serial.rs
new file mode 100644
index 0000000..03fa570
--- /dev/null
+++ b/src/serial.rs
@@ -0,0 +1,118 @@
+/// UART 16550 serial driver — port-mapped I/O on COM1 (0x3F8)
+use core::fmt;
+
+const COM1: u16 = 0x3F8;
+
+const DATA_REG: u16 = COM1;
+const INTR_ENABLE: u16 = COM1 + 1;
+const FIFO_CONTROL: u16 = COM1 + 2;
+const LINE_CONTROL: u16 = COM1 + 3;
+const MODEM_CONTROL: u16 = COM1 + 4;
+const LINE_STATUS: u16 = COM1 + 5;
+
+const LSR_TX_EMPTY: u8 = 0x20;
+const LSR_DATA_READY: u8 = 0x01;
+
+/// Initialise the UART with 115200 baud, 8N1.
+pub fn init() {
+    unsafe {
+        // Disable interrupts
+        port_out(INTR_ENABLE, 0x00);
+        // Set DLAB=1 (baud rate divisor)
+        port_out(LINE_CONTROL, 0x80);
+        // Divisor = 1 → 115200 baud (with 1.8432 MHz clock)
+        port_out(DATA_REG, 0x01);
+        port_out(INTR_ENABLE, 0x00);
+        // 8-bit, 1 stop, no parity, DLAB=0
+        port_out(LINE_CONTROL, 0x03);
+        // Enable FIFO, clear, 14-byte threshold
+        port_out(FIFO_CONTROL, 0xC7);
+        // RTS/DSR set
+        port_out(MODEM_CONTROL, 0x0B);
+    }
+}
+
+/// Write a single byte to the serial port (blocking poll).
+pub fn put_byte(b: u8) {
+    unsafe {
+        // Wait for transmitter holding register empty
+        while port_in(LINE_STATUS) & LSR_TX_EMPTY == 0 {}
+        port_out(DATA_REG, b);
+    }
+}
+
+/// Read a single byte from the serial port (blocking poll).
+pub fn get_byte() -> u8 {
+    unsafe {
+        while port_in(LINE_STATUS) & LSR_DATA_READY == 0 {}
+        port_in(DATA_REG)
+    }
+}
+
+/// Non-blocking read: returns Some(byte) if data ready, None otherwise.
+pub fn try_get_byte() -> Option<u8> {
+    unsafe {
+        if port_in(LINE_STATUS) & LSR_DATA_READY != 0 {
+            Some(port_in(DATA_REG))
+        } else {
+            None
+        }
+    }
+}
+
+/// Write a string to serial.
+pub fn write_str(s: &str) {
+    for &b in s.as_bytes() {
+        if b == b'\n' {
+            put_byte(b'\r');
+        }
+        put_byte(b);
+    }
+}
+
+// ---------------------------------------------------------------------------
+// fmt::Write implementation
+// ---------------------------------------------------------------------------
+pub struct SerialWriter;
+
+impl fmt::Write for SerialWriter {
+    fn write_str(&mut self, s: &str) -> fmt::Result {
+        write_str(s);
+        Ok(())
+    }
+}
+
+/// Helper macro — prints to serial via format_args!.
+#[macro_export]
+macro_rules! serial_print {
+    ($($arg:tt)*) => {{
+        use core::fmt::Write;
+        let _ = write!(&mut $crate::serial::SerialWriter, $($arg)*);
+    }};
+}
+
+#[macro_export]
+macro_rules! serial_println {
+    () => { $crate::serial::write_str("\r\n"); };
+    ($($arg:tt)*) => {{
+        $crate::serial_print!($($arg)*);
+        $crate::serial::write_str("\r\n");
+    }};
+}
+
+// ---------------------------------------------------------------------------
+// Port I/O helpers
+// ---------------------------------------------------------------------------
+unsafe fn port_in(port: u16) -> u8 {
+    let val: u8;
+    unsafe {
+        core::arch::asm!("in al, dx", out("al") val, in("dx") port, options(nostack, preserves_flags));
+    }
+    val
+}
+
+unsafe fn port_out(port: u16, val: u8) {
+    unsafe {
+        core::arch::asm!("out dx, al", in("al") val, in("dx") port, options(nostack, preserves_flags));
+    }
+}