ardupilot/libraries/AP_Scheduler/AP_Scheduler.cpp

/// -*- tab-width: 4; Mode: C++; c-basic-offset: 4; indent-tabs-mode: nil -*-
/*
   This program is free software: you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation, either version 3 of the License, or
   (at your option) any later version.

   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.

   You should have received a copy of the GNU General Public License
   along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

/*
 *  main loop scheduler for APM
 *  Author: Andrew Tridgell, January 2013
 *
 */
#include "AP_Scheduler.h"

#include <AP_HAL/AP_HAL.h>
#include <AP_Param/AP_Param.h>
#include <AP_Vehicle/AP_Vehicle.h>

#if APM_BUILD_TYPE(APM_BUILD_ArduCopter)
#define SCHEDULER_DEFAULT_LOOP_RATE 400
#define SCHEDULER_EXPOSE_LOOP_RATE_PARAMETER 0
#else
#define SCHEDULER_DEFAULT_LOOP_RATE  50
#define SCHEDULER_EXPOSE_LOOP_RATE_PARAMETER 1
#endif

extern const AP_HAL::HAL& hal;

int8_t AP_Scheduler::current_task = -1;

const AP_Param::GroupInfo AP_Scheduler::var_info[] = {
    // @Param: DEBUG
    // @DisplayName: Scheduler debug level
    // @Description: Set to non-zero to enable scheduler debug messages. When set to show "Slips" the scheduler will display a message whenever a scheduled task is delayed due to too much CPU load. When set to ShowOverruns the scheduled will display a message whenever a task takes longer than the limit promised in the task table.
    // @Values: 0:Disabled,2:ShowSlips,3:ShowOverruns
    // @User: Advanced
    AP_GROUPINFO("DEBUG",    0, AP_Scheduler, _debug, 0),

#if SCHEDULER_EXPOSE_LOOP_RATE_PARAMETER
    // @Param: LOOP_RATE
    // @DisplayName: Scheduling main loop rate
    // @Description: This controls the rate of the main control loop in Hz. This should only be changed by developers. This only takes effect on restart
    // @Values: 50:50Hz,100:100Hz,200:200Hz,250:250Hz,300:300Hz,400:400Hz
    // @RebootRequired: True
    // @User: Advanced
    AP_GROUPINFO("LOOP_RATE",  1, AP_Scheduler, _loop_rate_hz, SCHEDULER_DEFAULT_LOOP_RATE),
#endif

    AP_GROUPEND
};

// constructor
AP_Scheduler::AP_Scheduler(void)
{
#if !SCHEDULER_EXPOSE_LOOP_RATE_PARAMETER
    _loop_rate_hz.set(SCHEDULER_DEFAULT_LOOP_RATE);
#endif
    AP_Param::setup_object_defaults(this, var_info);

    // only allow 50 to 400 Hz
    if (_loop_rate_hz < 50) {
        _loop_rate_hz.set(50);
    } else if (_loop_rate_hz > 400) {
        _loop_rate_hz.set(400);
    }
}

// initialise the scheduler
void AP_Scheduler::init(const AP_Scheduler::Task *tasks, uint8_t num_tasks)
{
    _tasks = tasks;
    _num_tasks = num_tasks;
    _last_run = new uint16_t[_num_tasks];
    memset(_last_run, 0, sizeof(_last_run[0]) * _num_tasks);
    _tick_counter = 0;
}

// one tick has passed
void AP_Scheduler::tick(void)
{
    _tick_counter++;
}

/*
  run one tick
  this will run as many scheduler tasks as we can in the specified time
 */
void AP_Scheduler::run(uint16_t time_available)
{
    uint32_t run_started_usec = AP_HAL::micros();
    uint32_t now = run_started_usec;

    for (uint8_t i=0; i<_num_tasks; i++) {
        uint16_t dt = _tick_counter - _last_run[i];
        uint16_t interval_ticks = _loop_rate_hz / _tasks[i].rate_hz;
        if (interval_ticks < 1) {
            interval_ticks = 1;
        }
        if (dt >= interval_ticks) {
            // this task is due to run. Do we have enough time to run it?
            _task_time_allowed = _tasks[i].max_time_micros;

            if (dt >= interval_ticks*2) {
                // we've slipped a whole run of this task!
                if (_debug > 1) {
                    hal.console->printf("Scheduler slip task[%u-%s] (%u/%u/%u)\n",
                                          (unsigned)i,
                                          _tasks[i].name,
                                          (unsigned)dt,
                                          (unsigned)interval_ticks,
                                          (unsigned)_task_time_allowed);
                }
            }

            if (_task_time_allowed <= time_available) {
                // run it
                _task_time_started = now;
                current_task = i;
                _tasks[i].function();
                current_task = -1;

                // record the tick counter when we ran. This drives
                // when we next run the event
                _last_run[i] = _tick_counter;

                // work out how long the event actually took
                now = AP_HAL::micros();
                uint32_t time_taken = now - _task_time_started;

                if (time_taken > _task_time_allowed) {
                    // the event overran!
                    if (_debug > 2) {
                        hal.console->printf("Scheduler overrun task[%u-%s] (%u/%u)\n",
                                              (unsigned)i,
                                              _tasks[i].name,
                                              (unsigned)time_taken,
                                              (unsigned)_task_time_allowed);
                    }
                }
                if (time_taken >= time_available) {
                    goto update_spare_ticks;
                }
                time_available -= time_taken;
            }
        }
    }

    // update number of spare microseconds
    _spare_micros += time_available;

update_spare_ticks:
    _spare_ticks++;
    if (_spare_ticks == 32) {
        _spare_ticks /= 2;
        _spare_micros /= 2;
    }
}

/*
  return number of micros until the current task reaches its deadline
 */
uint16_t AP_Scheduler::time_available_usec(void)
{
    uint32_t dt = AP_HAL::micros() - _task_time_started;
    if (dt > _task_time_allowed) {
        return 0;
    }
    return _task_time_allowed - dt;
}

/*
  calculate load average as a number from 0 to 1
 */
float AP_Scheduler::load_average(uint32_t tick_time_usec) const
{
    if (_spare_ticks == 0) {
        return 0.0f;
    }
    uint32_t used_time = tick_time_usec - (_spare_micros/_spare_ticks);
    return used_time / (float)tick_time_usec;
}