genode/repos/base-hw/src/core/kernel/clock.cc

/*
 * \brief   A clock manages a continuous time and timeouts on it
 * \author  Martin Stein
 * \date    2016-03-23
 */

/*
 * Copyright (C) 2016-2017 Genode Labs GmbH
 *
 * This file is part of the Genode OS framework, which is distributed
 * under the terms of the GNU Affero General Public License version 3.
 */

/* Core includes */
#include <kernel/clock.h>
#include <hw/assert.h>

using namespace Kernel;


time_t Clock::us_to_tics(time_t const us) const
{
	return _timer->us_to_tics(us);
}


time_t Clock::timeout_age_us(Timeout const * const timeout) const
{
	time_t const age = (time_t)_time - timeout->_start;
	return _timer->tics_to_us(age);
}


time_t Clock::timeout_max_us() const
{
	return _timer->tics_to_us(_timer->max_value());
}


bool Clock::_time_overflow(time_t const duration) const
{
	return duration > ~(time_t)0 - _time;
}


void Clock::set_timeout(Timeout * const timeout, time_t const duration)
{
	/*
	 * Remove timeout if it is already in use. Timeouts may get overridden as
	 * result of an update.
	 */
	if (timeout->_listed) {
		_timeout_list[timeout->_end_period].remove(timeout);
	} else {
		timeout->_listed = true; }

	/* set timeout parameters */
	timeout->_start      = _time;
	timeout->_end        = _time + duration;
	timeout->_end_period = _time_overflow(duration) ? !_time_period :
	                                                   _time_period;

	/*
	 * Insert timeout. Timeouts are ordered ascending according to their end
	 * time to be able to quickly determine the nearest timeout.
	 */
	Genode::List<Timeout> & list = _timeout_list[timeout->_end_period];
	Timeout * t1 = 0;
	for (Timeout * t2 = list.first(); t2 && t2->_end < timeout->_end;
	     t1 = t2, t2 = t2->next()) { }

	list.insert(timeout, t1);
}


void Clock::schedule_timeout()
{
	/* get the timeout with the nearest end time */
	Timeout * timeout = _timeout_list[_time_period].first();
	if (!timeout) {
		timeout = _timeout_list[!_time_period].first();
		assert(timeout);
	}
	/* install timeout at timer hardware */
	time_t const duration = (time_t)timeout->_end - _time;
	_last_timeout_duration = duration;
	_timer->start_one_shot(duration, _cpu_id);
}


time_t Clock::update_time()
{
	/* determine how much time has passed */
	time_t const old_value = _last_timeout_duration;
	time_t const new_value = _timer->value(_cpu_id);
	time_t const duration  = old_value > new_value ? old_value - new_value : 1;

	/* is this the end of the current period? */
	if (_time_overflow(duration)) {

		/* flush all timeouts of current period */
		Genode::List<Timeout> & list = _timeout_list[_time_period];
		while (true) {
			Timeout * const timeout = list.first();
			if (!timeout) { break; }
			list.remove(timeout);
			timeout->_listed = false;
			timeout->timeout_triggered();
		}
		/* switch to next period */
		_time_period = !_time_period;

	}
	/* update time */
	_time += duration;
	return duration;
}


void Clock::process_timeouts()
{
	/*
	 * Walk through timeouts until the first whose end time is in the future.
	 * Consider only the current periods list as all timeouts of the next
	 * period must be in the future.
	 */
	Genode::List<Timeout> & list = _timeout_list[_time_period];
	while (true) {
		Timeout * const timeout = list.first();
		if (!timeout) { break; }
		if (timeout->_end > _time) { break; }
		list.remove(timeout);
		timeout->_listed = false;
		timeout->timeout_triggered();
	}
}


Clock::Clock(unsigned const cpu_id, Timer * const timer)
:
	_cpu_id(cpu_id), _timer(timer) { }