#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));
  }
}