pit.c

/*
 * Copyright (C) 2015, Intel Corporation. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * 3. Neither the name of the copyright holder nor the names of its
 *    contributors may be used to endorse or promote products derived
 *    from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE
 * COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
 * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
 * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
 * OF THE POSSIBILITY OF SUCH DAMAGE.
 */

#include <math.h>

#include "drivers/legacy_pc/pic.h"
#include "drivers/legacy_pc/pit.h"
#include "helpers.h"
#include "interrupt.h"

/* PCs usually provide an 8254 PIT chip with maximum clock of 1.193182 MHz. */
#define PIT_CONTROL_PORT    0x43
#define PIT_COUNTER0_PORT   0x40
#define PIT_CLOCK_FREQUENCY 1193182
#define PIT_IRQ 0
#define PIT_INT PIC_INT(PIT_IRQ)

static pit_int_callback interrupt_cb;

static void
pit_int_handler(void)
{
  interrupt_cb();

  pic_eoi(PIT_IRQ);
}
/*---------------------------------------------------------------------------*/
void
pit_init(uint32_t ticks_rate, pit_int_callback cb)
{
  SET_INTERRUPT_HANDLER(PIT_INT, 0, pit_int_handler);

  interrupt_cb = cb;

  /* Calculate the 16bit divisor that can provide the chosen clock tick rate
   * (CLOCK_CONF_SECOND in contiki-conf.h). For reference --> tick rate = clock frequency / divisor.
   * If we provide an odd divisor to the Square Wave generator (Mode 3) of
   * the Counter0, the duty cycle won't be exactly 50%, so we always round
   * it to nearest even integer.
   */
  uint16_t divisor = rint(PIT_CLOCK_FREQUENCY / ticks_rate);

  /* Setup Control register flags in a didactic way. */
  uint8_t flags = 0x30; /* Set bits 7:6 to select Counter0 and 5:4 to select "write 7:0 bits first". */
  flags |= 0x6;         /* Set bits 3:1 to Mode 3 and bit 0 to BCD off. */

  outb(PIT_CONTROL_PORT, flags);

  outb(PIT_COUNTER0_PORT, divisor & 0xFF); /* Write least significant bytes first. */
  outb(PIT_COUNTER0_PORT, (divisor >> 8) & 0xFF);

  pic_unmask_irq(PIT_IRQ);
}