Wait until serial tx buffer is empty

src/kernel/arch/x86_64/serial.rs

@@ -9,6 +9,8 @@ use num_derive::FromPrimitive;
 use num_traits::FromPrimitive;
 use x86_64::instructions::port::Port;
 
+use crate::arch::asm::nop;
+
 /// Represents an x86 port-mapped serial port.
 pub struct SerialPort {
     base_port: Port<u8>,
@@ -21,6 +23,7 @@ pub struct SerialPort {
     scratch: Port<u8>,
     fifo_register: u8,
     pub crlf: Crlf,
+    pub wait_tx_clear: bool,
 }
 
 #[derive(PartialEq, Eq)]
@@ -123,7 +126,6 @@ pub enum ModemStatus {
     DataCarrierDetect = 0b10000000,
 }
 
-// TODO: Ensure we don't clobber the tx buffer and prevent some data from getting printed
 impl SerialPort {
     pub fn log_write(&mut self, msg: &str) {
         if self.crlf == Crlf::Crlf {
@@ -140,10 +142,18 @@ impl SerialPort {
         }
     }
 
+    /// Get whether the transmit buffer is empty.
     pub fn is_transmit_empty(&mut self) -> bool {
-        self.get_interrupt_state() != InterruptState::TransmitterEmpty
+        self.get_line_status().contains(LineStatus::TransmitterEmpty)
     }
 
+    fn block_until_transmit_empty(&mut self) {
+        while !self.is_transmit_empty() {
+            nop();
+        }
+    }
+
+    /// Write a message with a newline appended to the serial port.
     pub fn log_writeln(&mut self, msg: &str) {
         self.log_write(msg);
         self.log_write("\n");
@@ -162,6 +172,7 @@ impl SerialPort {
             scratch: Port::new(port_addr + 7),
             fifo_register: 0,
             crlf: Crlf::Crlf,
+            wait_tx_clear: true,
         };
         // ensure this is false
         port.set_dlab(false);
@@ -190,6 +201,10 @@ impl SerialPort {
     }
     /// Write a single character to the TX buffer.
     pub fn write_char(&mut self, c: char) {
+        // Wait for the TX Buffer to be empty
+        if self.wait_tx_clear {
+            self.block_until_transmit_empty();
+        }
         unsafe { self.base_port.write(c as u8) };
     }