/* 
 * Copyright 2010 Stefan Lankes, Chair for Operating Systems,
 *                               RWTH Aachen University
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *
 * This file is part of MetalSVM.
 */

#include <metalsvm/stdio.h>
#include <metalsvm/string.h>
#include <metalsvm/tasks.h>
#include <metalsvm/time.h>
#include <metalsvm/processor.h>
#include <asm/apic.h>
#include <asm/irq.h>
#include <asm/irqflags.h>
#include <asm/gdt.h>
#include <asm/tss.h>
#include <asm/vga.h>

/* 
 * This will keep track of how many ticks the system
 * has been running for 
 */
static volatile uint64_t timer_ticks = 0;

/* 
 * Handles the timer. In this case, it's very simple: We
 * increment the 'timer_ticks' variable every time the
 * timer fires. 
 */
static void timer_handler(struct state *s)
{
	/* Increment our 'tick counter' */
	timer_ticks++;

	/* 
         * Every TIMER_FREQ clocks (approximately 1 second), we will
	 * display a message on the screen 
         */
	/*if (timer_ticks % TIMER_FREQ == 0) {
		vga_puts("One second has passed\n");
	}*/
}

/* 
 * This will continuously loop until the given time has
 * been reached 
 */
void timer_wait(unsigned int ticks)
{
	uint64_t eticks = timer_ticks + ticks;

	while (timer_ticks < eticks) 
		reschedule();
}

#define LATCH(f)	((CLOCK_TICK_RATE + f/2) / f)

/* 
 * Sets up the system clock by installing the timer handler
 * into IRQ0 
 */
int timer_init(void)
{
	uint64_t start;

	/* Installs 'timer_handler' to IRQ0 */
	irq_install_handler(0, timer_handler);

	if (!has_apic()) {
		/* set default timer */
		outportb(0x43, 0x34);
		start = rdtsc();
		while(rdtsc() - start < 1000000)
			;
		outportb(0x40, LATCH(TIMER_FREQ) & 0xFF);   /* low byte  */
		start = rdtsc();
		while(rdtsc() - start < 1000000)
			;
		outportb(0x40, LATCH(TIMER_FREQ) >> 8);     /* high byte */
	}

	return 0;
}