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 *   Copyright (C) 2012 PX4 Development Team. All rights reserved.
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 * modification, are permitted provided that the following conditions
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 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
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 *    notice, this list of conditions and the following disclaimer in
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 *    used to endorse or promote products derived from this software
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 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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/**
 * @file drv_hrt.h
 *
 * High-resolution timer with callouts and timekeeping.
 */

#pragma once

#include <sys/types.h>
#include <stdbool.h>
#include <inttypes.h>

#include <time.h>
#include <queue.h>

__BEGIN_DECLS

/*
 * Absolute time, in microsecond units.
 *
 * Absolute time is measured from some arbitrary epoch shortly after
 * system startup.  It should never wrap or go backwards.
 */
typedef uint64_t	hrt_abstime;

/*
 * Callout function type.
 *
 * Note that callouts run in the timer interrupt context, so
 * they are serialised with respect to each other, and must not
 * block.
 */
typedef void	(* hrt_callout)(void *arg);

/*
 * Callout record.
 */
typedef struct hrt_call {
	struct sq_entry_s	link;

	hrt_abstime		deadline;
	hrt_abstime		period;
	hrt_callout		callout;
	void			*arg;
} *hrt_call_t;

/*
 * Get absolute time.
 */
__EXPORT extern hrt_abstime hrt_absolute_time(void);

/*
 * Convert a timespec to absolute time.
 */
__EXPORT extern hrt_abstime ts_to_abstime(struct timespec *ts);

/*
 * Convert absolute time to a timespec.
 */
__EXPORT extern void	abstime_to_ts(struct timespec *ts, hrt_abstime abstime);

/*
 * Compute the delta between a timestamp taken in the past
 * and now.
 *
 * This function is safe to use even if the timestamp is updated
 * by an interrupt during execution.
 */
__EXPORT extern hrt_abstime hrt_elapsed_time(const volatile hrt_abstime *then);

/*
 * Store the absolute time in an interrupt-safe fashion.
 *
 * This function ensures that the timestamp cannot be seen half-written by an interrupt handler.
 */
__EXPORT extern hrt_abstime hrt_store_absolute_time(volatile hrt_abstime *now);

/*
 * Call callout(arg) after delay has elapsed.
 *
 * If callout is NULL, this can be used to implement a timeout by testing the call
 * with hrt_called().
 */
__EXPORT extern void	hrt_call_after(struct hrt_call *entry, hrt_abstime delay, hrt_callout callout, void *arg);

/*
 * Call callout(arg) at absolute time calltime.
 */
__EXPORT extern void	hrt_call_at(struct hrt_call *entry, hrt_abstime calltime, hrt_callout callout, void *arg);

/*
 * Call callout(arg) after delay, and then after every interval.
 *
 * Note thet the interval is timed between scheduled, not actual, call times, so the call rate may
 * jitter but should not drift.
 */
__EXPORT extern void	hrt_call_every(struct hrt_call *entry, hrt_abstime delay, hrt_abstime interval,
				       hrt_callout callout, void *arg);

/*
 * If this returns true, the entry has been invoked and removed from the callout list,
 * or it has never been entered.
 *
 * Always returns false for repeating callouts.
 */
__EXPORT extern bool	hrt_called(struct hrt_call *entry);

/*
 * Remove the entry from the callout list.
 */
__EXPORT extern void	hrt_cancel(struct hrt_call *entry);

/*
 * initialise a hrt_call structure
 */
__EXPORT extern void	hrt_call_init(struct hrt_call *entry);

/*
 * delay a hrt_call_every() periodic call by the given number of
 * microseconds. This should be called from within the callout to
 * cause the callout to be re-scheduled for a later time. The periodic
 * callouts will then continue from that new base time at the
 * previously specified period.
 */
__EXPORT extern void	hrt_call_delay(struct hrt_call *entry, hrt_abstime delay);

/*
 * Initialise the HRT.
 */
__EXPORT extern void	hrt_init(void);

__END_DECLS