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_HAL.h>
#include <AP_Scheduler.h>
#include <AP_Param.h>

extern const AP_HAL::HAL& hal;

const AP_Param::GroupInfo AP_Scheduler::var_info[] PROGMEM = {
    // @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,1:ShowSlips,2:ShowOverruns
    // @User: Advanced
    AP_GROUPINFO("DEBUG",    0, AP_Scheduler, _debug, 0),
    AP_GROUPEND
};

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

            if (dt >= interval_ticks*2) {
                // we've slipped a whole run of this task!
                if (_debug != 0) {
                    hal.console->printf_P(PSTR("Scheduler slip task[%u] (%u/%u/%u)\n"), 
                                          (unsigned)i, 
                                          (unsigned)dt,
                                          (unsigned)interval_ticks,
                                          (unsigned)_task_time_allowed);
                }
            }
            if (_task_time_allowed <= time_available) {
                // run it
                _task_time_started = hal.scheduler->micros();
                task_fn_t func = (task_fn_t)pgm_read_pointer(&_tasks[i].function);
                func();
                
                // 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
                uint32_t time_taken = hal.scheduler->micros() - _task_time_started;
                
                if (time_taken > _task_time_allowed) {
                    // the event overran!
                    if (_debug > 1) {
                        hal.console->printf_P(PSTR("Scheduler overrun task[%u] (%u/%u)\n"), 
                                              (unsigned)i, 
                                              (unsigned)time_taken,
                                              (unsigned)_task_time_allowed);
                    }
                    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 = hal.scheduler->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;
}