/*
 * Copyright (C) 2013 Freie Universität Berlin
 *
 * This file is subject to the terms and conditions of the GNU Lesser
 * General Public License v2.1. See the file LICENSE in the top level
 * directory for more details.
 */

/**
 * @defgroup    core_hwtimer Hardware timer
 * @ingroup     core
 * @brief       Hardware timer interface
 *
 * The Hardware timers are directly mapped to hardware timers with minimum
 * latency. They are intended for short intervals and to be used in time
 * critical low-level drivers (e.g. radio). hwtimer callbacks are run in the
 * interrupt context and must use the shortest possible execution time (e.g.
 * set a flag and trigger a worker thread).
 *
 * <b>The hardware timer should not be used (until you know what
 * you're doing)</b>, use \ref sys_vtimer instead.
 *
 * @{
 *
 * @file
 * @brief       HW-timer abstraction
 *
 * @author      Heiko Will
 * @author      Kaspar Schleiser <kaspar@schleiser.de>
 * @author      Michael Baar
 */

#ifndef HWTIMER_H
#define HWTIMER_H

#include <stdint.h>
#include "hwtimer_cpu.h"
#include "board.h"

#ifdef __cplusplus
 extern "C" {
#endif

/**
 * @brief   Number of kernel timer ticks per second
 * @def     HWTIMER_SPEED
 */
#ifndef HWTIMER_SPEED
#warning "HWTIMER_SPEED undefined. Set HWTIMER_SPEED to the number of ticks \
per second for the current architecture."
#endif

/**
 * @brief       Upper bound for hwtimer_spin
 *
 * @note        Barrier starting from which hwtimer_spin is called instead
 *              of setting a timer and yielding the thread.
 *
 *              Boards should override this.
 *
 * @def         HWTIMER_SPIN_BARRIER
 */
#ifndef HWTIMER_SPIN_BARRIER
#define HWTIMER_SPIN_BARRIER (6)
#endif

/**
 * @brief       Overhead of the `hwtimer_wait` function
 *
 * @note        This value is used to decrease the number of ticks that
 *              `hwtimer_wait` uses to set the actual hardware timer.
 *
 *              The goal is to make sure the number of ticks spent in the
 *              function corresponds to the ticks argument it was given.
 *
 *              Boards should override this.
 *
 * @def         HWTIMER_WAIT_OVERHEAD
 */
#ifndef HWTIMER_WAIT_OVERHEAD
#define HWTIMER_WAIT_OVERHEAD (2)
#endif

/**
 * @brief       Convert microseconds to kernel timer ticks
 * @param[in]   us number of microseconds
 * @return      kernel timer ticks
 */
#if HWTIMER_SPEED > 1000000L
#define HWTIMER_TICKS(us)        ((us) * (HWTIMER_SPEED / 1000000L))
#else
#define HWTIMER_TICKS(us)        ((us) / (1000000L / HWTIMER_SPEED))
#endif

/**
 * @brief       Convert ticks to microseconds
 * @param[in]   ticks   number of ticks
 * @return      microseconds
 */
#if HWTIMER_SPEED > 1000000L
#define HWTIMER_TICKS_TO_US(ticks)        ((ticks) / (HWTIMER_SPEED / 1000000L))
#else
#define HWTIMER_TICKS_TO_US(ticks)        ((ticks) * (1000000L / HWTIMER_SPEED))
#endif

/**
 * @brief   Maximum hwtimer tick count (before overflow)
 * @def     HWTIMER_MAXTICKS
 */
#ifndef HWTIMER_MAXTICKS
#warning "HWTIMER_MAXTICKS undefined. Set HWTIMER_MAXTICKS to the maximum \
number of ticks countable on the current architecture."
#endif

/**
 * @brief   microseconds before hwtimer overflow
 */
#if HWTIMER_SPEED > 1000000L
#define HWTIMER_OVERFLOW_MICROS()        (HWTIMER_MAXTICKS / HWTIMER_SPEED * 1000000L)
#else
#define HWTIMER_OVERFLOW_MICROS()        (1000000L / HWTIMER_SPEED * HWTIMER_MAXTICKS)
#endif

typedef uint32_t timer_tick_t; /**< data type for hwtimer ticks */

/**
 * @brief   initialize the hwtimer module
 */
void hwtimer_init(void);

/**
 * @brief   Get the hardware time
 * @return  The current tick count of the hardware timer
 */
unsigned long hwtimer_now(void);

/**
 * @brief Set a kernel timer
 * @param[in]   offset      Offset until callback invocation in timer ticks
 * @param[in]   callback    Callback function
 * @param[in]   ptr         Argument to callback function
 * @return      timer id
 */
int hwtimer_set(unsigned long offset, void (*callback)(void*), void *ptr);

/**
 * @brief Set a kernel timer
 * @param[in]   absolute    Absolute timer counter value for invocation
 *                          of handler
 * @param[in]   callback    Callback function
 * @param[in]   ptr         Argument to callback function
 * @return      timer id
 */
int hwtimer_set_absolute(unsigned long absolute,
        void (*callback)(void*), void *ptr);

/**
 * @brief Remove a kernel timer
 * @param[in]   t   Id of timer to remove
 * @return      1 on success
 */
int hwtimer_remove(int t);

/**
 * @brief        Delay current thread
 * @param[in]    ticks  Number of kernel ticks to delay
 */
void hwtimer_wait(unsigned long ticks);

/**
 * @brief   determine if the hwtimer module is initialized
 * @return  1 if the hwtimer module is initialized
 */
int hwtimer_active(void);

/**
 * @brief       initialize hwtimer module data structures and hardware
 *
 * @param[in]   fcpu        cpu frequency
 */
void hwtimer_init_comp(uint32_t fcpu);

/**
 * @brief       Delay current thread, spinning. Use only in interrupts for
 *              VERY short delays!
 *
 * @param[in]   ticks        Number of kernel ticks to delay
 */
void hwtimer_spin(unsigned long ticks);

#ifdef __cplusplus
}
#endif

/** @} */
#endif /* HWTIMER_H */