Add support for serial port output

5 files changed, 104 insertions, 44 deletions

diff --git a/Makefile b/Makefile
index f248f46..c5e8bdc 100644
--- a/Makefile
+++ b/Makefile
@@ -1,7 +1,9 @@
 all: target/kernel.o
 
+clean_run: | clean run
+
 run: target/kernel.o
-	qemu-system-i386 -kernel $< -machine type=pc-i440fx-3.1
+	qemu-system-i386 -kernel $< -machine type=pc-i440fx-3.1 -serial stdio
 
 target/boot.o: boot/boot.S
 	mkdir -p target
@@ -17,5 +19,5 @@ target/i686-lisibleos/release/libkernel.a:
 
 clean:
 	RUST_TARGET_PATH=$(shell pwd) xargo clean --target i686-lisibleos
-	rm target/kernel.o target/boot.o target/i686-lisibleos/debug/libkernel.a
-	rm target/kernel.o target/boot.o target/i686-lisibleos/release/libkernel.a
+	rm -f target/kernel.o target/boot.o target/i686-lisibleos/debug/libkernel.a
+	rm -f target/kernel.o target/boot.o target/i686-lisibleos/release/libkernel.a
diff --git a/kernel/src/io.rs b/kernel/src/io.rs
index def8665..a647408 100644
--- a/kernel/src/io.rs
+++ b/kernel/src/io.rs
@@ -1,5 +1,14 @@
 pub unsafe fn out8(address: u16, value: u8) {
     asm!(
-        "out dx, al", in("dx") address, in("al") value
-    )
+    "out dx, al", in("dx") address, in("al") value
+    );
+}
+
+pub unsafe fn in8(address: u16) -> u8 {
+    let result: u8;
+    asm!(
+    "in al, dx", in("dx") address, out("al") result
+    );
+
+    result
 }
diff --git a/kernel/src/lib.rs b/kernel/src/lib.rs
index edb5704..b1c8cf2 100644
--- a/kernel/src/lib.rs
+++ b/kernel/src/lib.rs
@@ -6,38 +6,20 @@ use crate::terminal::Terminal;
 use core::panic::PanicInfo;
 
 mod io;
+mod serial;
 mod terminal;
 
 #[no_mangle]
 pub extern "C" fn kmain() -> ! {
     let mut terminal = Terminal::new();
     terminal.clear();
-    terminal.put_string(b"1 LisibleOS\n");
-    terminal.put_string(b"2 > \n");
-    terminal.put_string(b"3\n");
-    terminal.put_string(b"4\n");
-    terminal.put_string(b"5\n");
-    terminal.put_string(b"6\n");
-    terminal.put_string(b"7\n");
-    terminal.put_string(b"8\n");
-    terminal.put_string(b"9\n");
-    terminal.put_string(b"10\n");
-    terminal.put_string(b"11\n");
-    terminal.put_string(b"12\n");
-    terminal.put_string(b"13\n");
-    terminal.put_string(b"14\n");
-    terminal.put_string(b"15\n");
-    terminal.put_string(b"16\n");
-    terminal.put_string(b"17\n");
-    terminal.put_string(b"18\n");
-    terminal.put_string(b"19\n");
-    terminal.put_string(b"20\n");
-    terminal.put_string(b"21\n");
-    terminal.put_string(b"22\n");
-    terminal.put_string(b"23\n");
-    terminal.put_string(b"24\n");
-    terminal.put_string(b"25\n");
-    terminal.put_string(b"26");
+    if let Err(_) = serial::initialize_serial_port() {
+        terminal.put_string(b"Serial port initialization failed");
+    } else {
+        terminal.put_string(b"Serial port initialization succeeded");
+    }
+
+    serial::write_bytes(b"This string was sent through the serial port!!");
     loop {}
 }
 
diff --git a/kernel/src/serial.rs b/kernel/src/serial.rs
new file mode 100644
index 0000000..77c15cb
--- /dev/null
+++ b/kernel/src/serial.rs
@@ -0,0 +1,66 @@
+use crate::io::{in8, out8};
+use crate::serial::SerialError::SerialPortInitializationFailed;
+
+const COM1_PORT: u16 = 0x3F8;
+const OFFSET_DATA_REGISTER: u8 = 0;
+const OFFSET_INTERRUPT_ENABLE_REGISTER: u8 = 1;
+const OFFSET_INTERRUPT_IDENTIFICATION_AND_FIFO_CONTROL_REGISTER: u8 = 2;
+const OFFSET_LINE_CONTROL_REGISTER: u8 = 3;
+const OFFSET_MODEM_CONTROL_REGISTER: u8 = 4;
+const OFFSET_LINE_STATUS_REGISTER: u8 = 5;
+
+#[derive(Debug)]
+pub enum SerialError {
+    SerialPortInitializationFailed,
+}
+
+pub fn initialize_serial_port() -> Result<(), SerialError> {
+    // Safety:
+    // These instructions read and write data on valid COM ports
+    unsafe {
+        out8(COM1_PORT + OFFSET_INTERRUPT_ENABLE_REGISTER as u16, 0x00);
+        out8(COM1_PORT + OFFSET_LINE_CONTROL_REGISTER as u16, 0x80);
+        out8(COM1_PORT + OFFSET_DATA_REGISTER as u16, 0x03);
+        out8(COM1_PORT + OFFSET_INTERRUPT_ENABLE_REGISTER as u16, 0x00);
+        out8(COM1_PORT + OFFSET_LINE_CONTROL_REGISTER as u16, 0x03);
+        out8(
+            COM1_PORT + OFFSET_INTERRUPT_IDENTIFICATION_AND_FIFO_CONTROL_REGISTER as u16,
+            0xC7,
+        );
+        out8(COM1_PORT + OFFSET_MODEM_CONTROL_REGISTER as u16, 0x0B);
+
+        // Testing the serial chip
+        out8(COM1_PORT + OFFSET_MODEM_CONTROL_REGISTER as u16, 0x1E); // Enable loopback mode
+        out8(COM1_PORT + OFFSET_DATA_REGISTER as u16, 0xAE);
+        if in8(COM1_PORT + OFFSET_DATA_REGISTER as u16) != 0xAE {
+            return Err(SerialPortInitializationFailed);
+        }
+
+        out8(COM1_PORT + OFFSET_MODEM_CONTROL_REGISTER as u16, 0x0F); // Enable normal mode
+    }
+
+    Ok(())
+}
+
+pub fn write(byte: u8) {
+    while !is_ready_to_send_data() {}
+    // Safety: the value is sent on a valid port address, which is the COM port
+    // data register address
+    unsafe {
+        out8(COM1_PORT, byte);
+    }
+}
+
+pub fn write_bytes(bytes: &[u8]) {
+    for &byte in bytes {
+        write(byte);
+    }
+}
+
+fn is_ready_to_send_data() -> bool {
+    const THRE_BIT: u8 = 0x20;
+
+    // Safety: the value is sent on a valid port address, which is the COM port
+    // line status register address
+    return unsafe { in8(COM1_PORT + OFFSET_LINE_STATUS_REGISTER as u16) } & THRE_BIT != 0;
+}
diff --git a/kernel/src/terminal.rs b/kernel/src/terminal.rs
index c64188c..63c7d95 100644
--- a/kernel/src/terminal.rs
+++ b/kernel/src/terminal.rs
@@ -1,15 +1,15 @@
 use crate::io;
 use compiler_builtins::mem::memcpy;
 
-const VGA_BUFFER_POINTER: *mut u8 = 0xb8000 as *mut u8;
+const VGA_BUFFER_POINTER: *mut u8 = 0xB8000 as *mut u8;
 const VGA_BUFFER_SIZE: u16 = 4000;
-const ROW_COUNT: u16 = 25;
-const COL_COUNT: u16 = 80;
-const VALUE_SIZE: u16 = 2;
+const ROW_COUNT: u8 = 25;
+const COL_COUNT: u8 = 80;
+const VALUE_SIZE: u8 = 2;
 
 pub(crate) struct Terminal {
-    current_row: u16,
-    current_col: u16,
+    current_row: u8,
+    current_col: u8,
 }
 
 impl Terminal {
@@ -67,9 +67,9 @@ impl Terminal {
         // The end pointer isn't past the VGA character buffer pointer
         // The offset doesn't overflow isize
         // The offset doesn't rely on wrapping around the address space
-        let src = unsafe { VGA_BUFFER_POINTER.offset((COL_COUNT * VALUE_SIZE) as isize) };
+        let src = unsafe { VGA_BUFFER_POINTER.offset(COL_COUNT as isize * VALUE_SIZE as isize) };
         let dest = VGA_BUFFER_POINTER;
-        let size = (VGA_BUFFER_SIZE - COL_COUNT) * VALUE_SIZE;
+        let size = (VGA_BUFFER_SIZE - COL_COUNT as u16) * VALUE_SIZE as u16;
 
         // Safety:
         // dest and src are valid pointer to the same object being the VGA character buffer
@@ -78,12 +78,13 @@ impl Terminal {
         self.clear_line(ROW_COUNT - 1);
     }
 
-    pub fn put_char_at(&mut self, c: u8, row: u16, col: u16) {
+    pub fn put_char_at(&mut self, c: u8, row: u8, col: u8) {
         self.current_row = row;
         self.current_col = col;
         unsafe {
             *VGA_BUFFER_POINTER.offset(
-                ((self.current_col + self.current_row * COL_COUNT) * VALUE_SIZE) as isize,
+                (self.current_col as isize + self.current_row as isize * COL_COUNT as isize)
+                    * VALUE_SIZE as isize,
             ) = c;
         }
     }
@@ -96,7 +97,7 @@ impl Terminal {
         self.current_row = 0;
     }
 
-    fn clear_line(&mut self, row: u16) {
+    fn clear_line(&mut self, row: u8) {
         for col in 0..COL_COUNT {
             self.put_char_at(b' ', row, col);
         }
@@ -105,8 +106,8 @@ impl Terminal {
         self.current_col = 0;
     }
 
-    pub fn set_cursor_position(&mut self, row: u16, col: u16) {
-        let cursor_position = row * COL_COUNT + col;
+    pub fn set_cursor_position(&mut self, row: u8, col: u8) {
+        let cursor_position = row as u16 * COL_COUNT as u16 + col as u16;
         let address_register = 0x3D4;
         let data_register = 0x3D5;
         unsafe {