contiki/cpu/x86/drivers/legacy_pc/pit.c

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/*
* 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);
}