/*
  Driver for serial output.
  Mostly useful for debug output because QEMU allows the redirection of serial output to either stdio or a file on the host computer.
*/

#include <types.h>
#include <port_io.h>
#include <string.h>

#include <drivers/serio.h>


#define COM1_IO_ADDR 0x3F8
#define COM2_IO_ADDR 0x2F8

#define COM1_IRQ 0x4
#define COM2_IRQ 0x3

#define COM1_LCR (COM1_IO_ADDR + 3)
#define COM2_LCR (COM2_IO_ADDR + 3)

#define BAUD 57600
#define DIVISOR 2


int serial_init(void)
{
  /* The following is taken from https://wiki.osdev.org/Serial_Ports */

  outb(COM1_IO_ADDR + 1, 0x00);    // Disable all interrupts
  outb(COM1_IO_ADDR + 3, 0x80);    // Enable DLAB (set baud rate divisor)
  outb(COM1_IO_ADDR + 0, 0x03);    // Set divisor to 3 (lo byte) 38400 baud
  outb(COM1_IO_ADDR + 1, 0x00);    //                  (hi byte)
  outb(COM1_IO_ADDR + 3, 0x03);    // 8 bits, no parity, one stop bit
  outb(COM1_IO_ADDR + 2, 0xC7);    // Enable FIFO, clear them, with 14-byte threshold
  outb(COM1_IO_ADDR + 4, 0x0B);    // IRQs enabled, RTS/DSR set
  outb(COM1_IO_ADDR + 4, 0x1E);    // Set in loopback mode, test the serial chip
  outb(COM1_IO_ADDR + 0, 0xAE);    // Test serial chip (send byte 0xAE and check if serial returns same byte)

  // Check if serial is faulty (i.e: not same byte as sent)
  if(inb(COM1_IO_ADDR + 0) != 0xAE)
  {
  return 1;
  }

  // If serial is not faulty set it in normal operation mode
  // (not-loopback with IRQs enabled and OUT#1 and OUT#2 bits enabled)
  outb(COM1_IO_ADDR + 4, 0x0F);
  return 0;
}

static int is_transmit_empty(void)
{
  return inb(COM1_IO_ADDR + 5) & 0x20;
}

static int serial_received(void)
{
  return inb(COM1_IO_ADDR + 5) & 1;
}

void serial_write(char a)
{
  while (is_transmit_empty() == 0);

  outb(COM1_IO_ADDR, a);
}

void serial_puts(const char* s)
{
  for (int i = 0; i < (int) strlen(s); i++)
  {
    serial_write(s[i]);
  }
}

char serial_read(void)
{
  while (serial_received() == 0);

  return inb(COM1_IO_ADDR);
}

bool use_serial(void)
{
  return true;
}