/*
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation. See the file COPYING
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * Copyright (C) 2010 Frank van Maarseveen <frankvm@frankvm.com>
 */

#include <stdint.h>
#include <avr/io.h>
#include <avr/interrupt.h>

#include "common.h"
#include "bits.h"
#include "boot.h"
#include "timer0.h"

/*
 * Timer/Counter0 implements two timestamp counters. An 8 bits wide 16usec
 * resolution timestamp counter is provided by TCNT0 using the 4 MHz system
 * clock divided by 64 (prescaler). It must not be written.
 * The "Timer/Counter0 Compare Match A" interrupt is used for implementing
 * a 32 bits wide millisecond resolution timestamp counter.
 */
void t0_init(void)
{
	OCR0A = TCNT0 + T0_MS;
	TCCR0B = _BV(CS01) | _BV(CS00);		/* 4MHz/64 */
	BIT_SET(TIMSK, OCIE0A);
}

void t0_cleanup(void)
{
	BIT_CLR(TIMSK, OCIE0A);
	TCCR0B = 0;
}

/*
 * Note that SPM page erase/write will halt the CPU for about 4 ms: they
 * cannot be timed this way and break subsequent t0_ms* calls until after
 * the first Timer/Counter0 Compare Match A interrupt or reinitialization.
 *
 * time: 10 us (estimation based on 40 words of code and 4MHz clock).
 */
static uint32_t millisec;
ISR(TIMER0_COMPA_vect)
{
	++millisec;
	OCR0A += T0_MS;
}

/*
 * Return the elapsed time in milliseconds. Usage:
 *
 *	uint32_t start = t0_ms(0);
 *	...
 *	elapsed = t0_ms(start);
 */
__attribute__((noinline))
uint32_t t0_ms(uint32_t start)
{
	uint32_t ms;
	uint8_t sreg;

	saveicli(sreg);
	ms = millisec;
	restorei(sreg);
	return ms - start;
}

/*
 * Wait `ms' milliseconds. The argument must not exceed 0x80000000.
 */
void t0_mswait(uint32_t ms)
{
	uint32_t t;

	t = t0_ms(0) + ms;
	while ((int32_t)t0_ms(t) < 0)
		;
}