1 files changed, 88 insertions, 0 deletions
diff --git a/drivers/serial.cc b/drivers/serial.cc
new file mode 100644
index 0000000..84dd4b0
--- /dev/null
+++ b/drivers/serial.cc
@@ -0,0 +1,88 @@
+#include "serial.h"
+
+/* Line Control
+ * | 7 | 6 | 5 | 4 | 3 | 2 | 1 | 0 |
+ * |dla|   | parity    | s | data  |
+ */
+enum LineControlRegister : uint8_t {
+  // data bits
+  d5bit = 0b00000000,
+  d6bit = 0b00000001,
+  d7bit = 0b00000010,
+  d8bit = 0b00000011,
+  // parity bits
+  none = 0b00000000,
+  odd = 0b00001000,
+  even = 0b00011000,
+  mark = 0b00101000,
+  space = 0b00111000,
+  // stop bits
+  s1bit = 0b00000000,
+  s2bit = 0b00000100,  // 1.5 for 5bit data; 2 otherwise
+  // divisor latch access bit
+  dlab = 0b10000000,
+};
+
+/* Line Status Register */
+enum LineStatusRegister : uint8_t {
+  DR = 0b00000001,    // data ready: see if there is data to read
+  OE = 0b00000010,    // overrun error: see if there has been data lost
+  PE = 0b00000100,    // parity error: see if there was error in transmission
+  FE = 0b00001000,    // framing error: see if a stop bit was missing
+  BI = 0b00010000,    // break indicator: see if there is a break in data input
+  THRE = 0b00100000,  // transmitter holding register empty: see if transmission buffer is empty
+  TEMT = 0b01000000,  // transmitter empty: see if transmitter is not doing anything
+  ERRO = 0b10000000,  // impending error: see if there is an error with a word in the input buffer
+};
+
+SerialPort::SerialPort() {
+  /*
+   * The serial controller (UART) has a baud rate of 115200 ticks per second; to limit the speed of the port set the
+   * divisor:
+   *   1. set DLAB on LineControl
+   *   2. set BaudDiv_l
+   *   3. set BaudDiv_h
+   *   4. clear LineControl
+   */
+
+  port.write(0x00, InterruptControl);  // disable all interrupts
+
+  port.write(dlab, LineControl);
+  port.write(0x03, BaudDiv_l);        // div_l: 0x03    38400 baud
+  port.write(0x00, BaudDiv_h);        // div_h: 0x00
+  port.write(d8bit | none | s1bit, LineControl);  // 8 bits, no parity, one stop bit
+
+  port.write(0xc7, FifoControl);      // enable FIFO, clear, with 14-byte threshold
+  port.write(0x0b, ModemControl);     // IRQ enabled, RTS/DSR set
+}
+
+bool SerialPort::ready_read() {
+  return (port.read(LineStatus) & DR);
+}
+
+uint8_t SerialPort::read() {
+  while (!ready_read()) {
+    asm volatile("nop");
+  }
+  return port.read();
+}
+
+bool SerialPort::ready_write() {
+  return (port.read(LineStatus) & THRE);
+}
+
+void SerialPort::write(char c) {
+  while (!ready_write()) {
+    asm volatile("nop");
+  }
+
+  switch (c) {
+    case '\n':
+      port.write('\n');
+      port.write('\r');
+      break;
+    default:
+      port.write(static_cast<uint8_t>(c));
+  }
+}
+