serial_port.h

#ifndef INCLUDE_SERIAL_PORT_H
#define INCLUDE_SERIAL_PORT_H


#include "io.h" /* io.h is implement in the section "Moving the cursor" */

/* The I/O port    com1: enabled=1, mode=file, dev=com1.outs */
/* All the I/O ports are calculated relative to the data port. This is because
* all serial ports (COM1, COM2, COM3, COM4) have their ports in the same
* order, but they start at different values.
*/

#define SERIAL_COM1_BASE                0x3F8      /* COM1 base port */

#define SERIAL_DATA_PORT(base)          (base)
#define SERIAL_FIFO_COMMAND_PORT(base)  (base + 2)
#define SERIAL_LINE_COMMAND_PORT(base)  (base + 3)
#define SERIAL_MODEM_COMMAND_PORT(base) (base + 4)
#define SERIAL_LINE_STATUS_PORT(base)   (base + 5)

/* The I/O port commands */

/* SERIAL_LINE_ENABLE_DLAB:
* Tells the serial port to expect first the highest 8 bits on the data port,
* then the lowest 8 bits will follow
*/
#define SERIAL_LINE_ENABLE_DLAB         0x80

void serial_configure_baud_rate(unsigned short com, unsigned short divisor) {
  /* Tell the serial port to first expect the highest 8 bits, then the lowest
   * 8 bits. This is done by sending 0x80 to the line command port
   */
  outb(SERIAL_LINE_COMMAND_PORT(com), SERIAL_LINE_ENABLE_DLAB);
  outb(SERIAL_DATA_PORT(com), (divisor >> 8) & 0x00FF);
  outb(SERIAL_DATA_PORT(com), divisor & 0x00FF);
}

void serial_configure_line(unsigned short com) {
  /* Bit:     | 7 | 6 | 5 4 3 | 2 | 1 0 |
   * Content: | d | b | prty  | s | dl  |
   * Value:   | 0 | 0 | 0 0 0 | 0 | 1 1 | = 0x03
   * data length of 8 bits, one stop bit, no parity bit, break control
   * disabled and DLAB disabled
   */
  outb(SERIAL_LINE_COMMAND_PORT(com), 0x03);
}

void serial_configure_fifo_buffer(unsigned short com) {
  /* Bit:     | 7 6 | 5  | 4 | 3   | 2   | 1   | 0 |
   * Content: | lvl | bs | r | dma | clt | clr | e |
   * Value:   | 1 1 | 0  | 0 | 0   | 1   | 1   | 1 | = 0xC7
   */
  outb(SERIAL_FIFO_COMMAND_PORT(com), 0xC7);
}

void serial_configure_modem(unsigned short com) {
  /* Bit:     | 7 | 6 | 5  | 4  | 3   | 2   | 1   | 0   |
   * Content: | r | r | af | lb | ao2 | ao1 | rts | dtr |
   * Value:   | 0 | 0 | 0  | 0  | 0   | 0   | 1   | 1 | = 0x03
   */
  outb(SERIAL_MODEM_COMMAND_PORT(com), 0x03);
}

int serial_is_transmit_fifo_empty(unsigned short com) {
  /* 0x20 = 0010 0000 */
  return inb(SERIAL_LINE_STATUS_PORT(com)) & 0x20;
}

void serial_configure(unsigned short port, unsigned short baudRate) {
  serial_configure_baud_rate(port, baudRate);
  serial_configure_line(port);
  serial_configure_fifo_buffer(port);
  serial_configure_modem(port);
}

void serial_write_byte(unsigned short port, char byteData) {
  outb(port, byteData);
}

int serial_write(unsigned short com, char *buf, unsigned int len) {
  unsigned int indexToBuffer = 0;
  while (indexToBuffer < len) {
    if (serial_is_transmit_fifo_empty(com)) {
      serial_write_byte(com, buf[indexToBuffer]);
      indexToBuffer++;
    }
  }
  return 0;
}

#endif