/* Copyright (c) 2012 The Chromium OS Authors. All rights reserved.
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 */

/* 1-wire interface module for Chrome EC */

#include "board.h"
#include "gpio.h"
#include "hooks.h"
#include "registers.h"
#include "timer.h"

#define ONEWIRE_PIN (1<<2)  /* One-wire pin mask (on GPIO H) */

/* Standard speed; all timings padded by 2 usec for safety.
 *
 * Note that these timing are actually _longer_ than legacy 1-wire standard
 * speed because we're running the 1-wire bus at 3.3V instead of 5V. */
#define T_RSTL 602  /* Reset low pulse; 600-960 us */
#define T_MSP   72  /* Presence detect sample time; 70-75 us */
#define T_RSTH (68 + 260 + 5 + 2) /* Reset high; tPDHmax + tPDLmax + tRECmin */
#define T_SLOT  70  /* Timeslot; >67 us */
#define T_W0L   63  /* Write 0 low; 62-120 us */
#define T_W1L    7  /* Write 1 low; 5-15 us */
#define T_RL     7  /* Read low; 5-15 us */
#define T_MSR    9  /* Read sample time; <15 us.  Must be at least 200 ns after
		     * T_RL since that's how long the signal takes to be pulled
		     * up on our board.  */


/* Output low on the bus for <usec> us, then switch back to open-drain input */
static void output0(int usec)
{
	LM4_GPIO_DIR(LM4_GPIO_H) |= ONEWIRE_PIN;
	LM4_GPIO_DATA(LM4_GPIO_H, ONEWIRE_PIN) = 0;
	udelay(usec);
	LM4_GPIO_DIR(LM4_GPIO_H) &= ~ONEWIRE_PIN;
}


/* Read the signal line */
static int readline(void)
{
	return LM4_GPIO_DATA(LM4_GPIO_H, ONEWIRE_PIN) ? 1 : 0;
}


/* Read a bit */
static int readbit(void)
{
	int bit;

	/* Output low */
	output0(T_RL);

	/* Delay to let slave release the line if it wants to send a 1-bit */
	udelay(T_MSR - T_RL);

	/* Read bit */
	bit = readline();

	/* Delay to end of timeslot */
	udelay(T_SLOT - T_MSR);
	return bit;
}


/* Write a bit */
static void writebit(int bit)
{
	if (bit) {
		output0(T_W1L);
		udelay(T_SLOT - T_W1L);
	} else {
		output0(T_W0L);
		udelay(T_SLOT - T_W0L);
	}
}


int onewire_reset(void)
{
	/* Start transaction with master reset pulse */
	output0(T_RSTL);

	/* Wait for presence detect sample time */
	udelay(T_MSP);
	/* Alternately, we could poll waiting for a 1-bit indicating our pulse
	 * has let go, then poll up to max time waiting for a 0-bit indicating
	 * the slave has responded. */
	if (readline() != 0)
		return EC_ERROR_UNKNOWN;

	/* Wait for end of presence pulse */
	/* Alternately, we could poll waiting for a 1-bit */
	udelay(T_RSTH - T_MSP);

	return EC_SUCCESS;
}


int onewire_read(void)
{
	int data = 0;
	int i;

	for (i = 0; i < 8; i++)
		data |= readbit() << i;  /* LSB first */

	return data;
}


void onewire_write(int data)
{
	int i;

	for (i = 0; i < 8; i++)
		writebit((data >> i) & 0x01);  /* LSB first */
}

/*****************************************************************************/
/* Initialization */

/* Configures GPIOs for the module. */
static void configure_gpio(void)
{
	/* Configure 1-wire pin as open-drain GPIO */
	gpio_set_alternate_function(LM4_GPIO_H, ONEWIRE_PIN, 0);
	LM4_GPIO_ODR(LM4_GPIO_H) |= ONEWIRE_PIN;
}


static int onewire_init(void)
{
	/* Configure GPIOs */
	configure_gpio();

	return EC_SUCCESS;
}
DECLARE_HOOK(HOOK_INIT, onewire_init, HOOK_PRIO_DEFAULT);