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

#include "common.h"
#include "hardware.h"
#include "types.h"
#include "bits.h"
#include "adc.h"

struct adc_config
{
	uint8_t			admux;		/* ADC config for this measurement */
	uint8_t			irqcount;	/* # measurements before picking another admux, >=2 */
	uint8_t			order;		/* need (1 << order) samples. should be <= 6 (10 bit ADC) */
	void			(*callback)(uint16_t value);
	uint8_t			count;		/* # samples we have */
	uint16_t		sum;		/* of the samples */
};

/*
 * ADC clock frequency is 125kHz => 8µs. Initial sample takes 25 cycles => 200µs.
 * Subsequent samples take 14 cycles => 112µs. Result time is approximately:
 *
 *	order 4: 1.8ms
 *	order 5: 3.6ms
 *	order 6: 7.2ms
 *
 * but actual times are appended in comment below (they may change as the code changes)
 */
static struct adc_config	adc_config[] = {
	/*  admux    irqcount  order	callback */
	{ ILED_ADMUX,	8,	4,	adc_iled},	/* 5-6ms */
	{ VBAT_ADMUX,	8,	4,	adc_vbat},	/* 5-6ms */
	{ TEMP_ADMUX,	1,	6,	adc_temp}	/* 344..345ms? */
};

static struct adc_config *	adcp;		/* what we currently measure */
static uint8_t			adc_pending;	/* # pending samples with current config */
static bool_t			adc_discard;	/* first sample will be discarded */
static uint8_t			adc_maxcount;	/* cached value for 1 << adcp->order */

__attribute__((noinline))
static void adc_setup(void)
{
	ADMUX = adcp->admux;
	adc_pending = adcp->irqcount;
	adc_discard = true;
	adc_maxcount = 1 << adcp->order;
}

void adc_init(void)
{
	/*
	 * Start the prescaler. This should be right after pwm1_init().
	 */
	ADCSRA = _BV(ADEN) |	/* enable */
		_BV(ADIE) |	/* interrupt enable */
		BIN8(101);	/* 4MHz/32 = 125kHz */
	adcp = adc_config;
	adc_setup();
}

void adc_cleanup(void)
{
	ADCSRA = 0;
	ADMUX = 0;
}

/*
 * 0x110 (worst case executed code size) / 2 (bytes per instruction) / 4 (MHz)
 * = 34 us. A minimalistic callback consisting of ee_min16() and ee_max16() calls
 * and assuming one of them calls ee_write_async() yields an additional
 * 0x20+0x1a+0x1a+0x28 = 0x7c code bytes. Summed up this is (0x110+0x7c)/2/4 == 49 us.
 *
 * The fast path (taken most of the time) is 0x82/2/4 = 16 us.
 */
ISR(ADC_vect)
{
	uint16_t value;

	if (adc_discard) {
		adc_discard = false;
		goto out;
	}
	adcp->sum += ADCW;
	if (++adcp->count == adc_maxcount) {
		value = (adcp->sum + (adc_maxcount >> 1)) >> adcp->order;
		adcp->count = 0;
		adcp->sum = 0;
		adcp->callback(value);
	}
	if (!--adc_pending) {
		if (++adcp == adc_config + ARRAYSIZE(adc_config))
			adcp = adc_config;
		adc_setup();
	}

 out:
	BIT_SET(ADCSRA, ADSC);
}