MicroBitSystemTimer.cpp

00001 /*
00002 The MIT License (MIT)
00003 
00004 Copyright (c) 2016 British Broadcasting Corporation.
00005 This software is provided by Lancaster University by arrangement with the BBC.
00006 
00007 Permission is hereby granted, free of charge, to any person obtaining a
00008 copy of this software and associated documentation files (the "Software"),
00009 to deal in the Software without restriction, including without limitation
00010 the rights to use, copy, modify, merge, publish, distribute, sublicense,
00011 and/or sell copies of the Software, and to permit persons to whom the
00012 Software is furnished to do so, subject to the following conditions:
00013 
00014 The above copyright notice and this permission notice shall be included in
00015 all copies or substantial portions of the Software.
00016 
00017 THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
00018 IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
00019 FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
00020 THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
00021 LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
00022 FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
00023 DEALINGS IN THE SOFTWARE.
00024 */
00025 
00026 /**
00027   * Definitions for the MicroBit system timer.
00028   *
00029   * This module provides:
00030   *
00031   * 1) a concept of global system time since power up
00032   * 2) a simple periodic multiplexing API for the underlying mbed implementation.
00033   *
00034   * The latter is useful to avoid costs associated with multiple mbed Ticker instances
00035   * in microbit-dal components, as each incurs a significant additional RAM overhead (circa 80 bytes).
00036   */
00037 #include "MicroBitConfig.h"
00038 #include "MicroBitSystemTimer.h"
00039 #include "ErrorNo.h"
00040 
00041 /*
00042  * Time since power on. Measured in milliseconds.
00043  * When stored as an unsigned long, this gives us approx 50 days between rollover, which is ample. :-)
00044  */
00045 static uint64_t time_us = 0;
00046 static unsigned int tick_period = 0;
00047 
00048 // Array of components which are iterated during a system tick
00049 static MicroBitComponent* systemTickComponents[MICROBIT_SYSTEM_COMPONENTS];
00050 
00051 // Periodic callback interrupt
00052 static Ticker *ticker = NULL;
00053 
00054 // System timer.
00055 static Timer *timer = NULL;
00056 
00057 
00058 /**
00059   * Initialises a system wide timer, used to drive the various components used in the runtime.
00060   *
00061   * This must be called before any components register to receive periodic periodic callbacks.
00062   *
00063   * @param timer_period The initial period between interrupts, in millseconds.
00064   *
00065   * @return MICROBIT_OK on success.
00066   */
00067 int system_timer_init(int period)
00068 {
00069     if (ticker == NULL)
00070         ticker = new Ticker();
00071 
00072     if (timer == NULL)
00073     {
00074         timer = new Timer();
00075         timer->start();
00076     }
00077 
00078     return system_timer_set_period(period);
00079 }
00080 
00081 /**
00082   * Reconfigures the system wide timer to the given period in milliseconds.
00083   *
00084   * @param period the new period of the timer in milliseconds
00085   *
00086   * @return MICROBIT_OK on success. MICROBIT_INVALID_PARAMETER is returned if period < 1
00087   */
00088 int system_timer_set_period(int period)
00089 {
00090     if (period < 1)
00091         return MICROBIT_INVALID_PARAMETER;
00092 
00093     // If a timer is already running, ensure it is disabled before reconfiguring.
00094     if (tick_period)
00095         ticker->detach();
00096 
00097     // register a period callback to drive the scheduler and any other registered components.
00098     tick_period = period;
00099     ticker->attach_us(system_timer_tick, period * 1000);
00100 
00101     return MICROBIT_OK;
00102 }
00103 
00104 /**
00105   * Accessor to obtain the current tick period in milliseconds
00106   *
00107   * @return the current tick period in milliseconds
00108   */
00109 int system_timer_get_period()
00110 {
00111     return tick_period;
00112 }
00113 
00114 /**
00115   * Updates the current time in microseconds, since power on.
00116   *
00117   * If the mbed Timer hasn't been initialised, it will be initialised
00118   * on the first call to this function.
00119   */
00120 void update_time()
00121 {
00122     // If we haven't been initialized, bring up the timer with the default period.
00123     if (timer == NULL || ticker == NULL)
00124         system_timer_init(SYSTEM_TICK_PERIOD_MS);
00125 
00126     time_us += timer->read_us();
00127     timer->reset();
00128 }
00129 
00130 /**
00131   * Determines the time since the device was powered on.
00132   *
00133   * @return the current time since power on in milliseconds
00134   */
00135 uint64_t system_timer_current_time()
00136 {
00137     return system_timer_current_time_us() / 1000;
00138 }
00139 
00140 /**
00141   * Determines the time since the device was powered on.
00142   *
00143   * @return the current time since power on in microseconds
00144   */
00145 uint64_t system_timer_current_time_us()
00146 {
00147     update_time();
00148     return time_us;
00149 }
00150 
00151 /**
00152   * Timer callback. Called from interrupt context, once per period.
00153   *
00154   * Simply checks to determine if any fibers blocked on the sleep queue need to be woken up
00155   * and made runnable.
00156   */
00157 void system_timer_tick()
00158 {
00159     update_time();
00160 
00161     // Update any components registered for a callback
00162     for(int i = 0; i < MICROBIT_SYSTEM_COMPONENTS; i++)
00163         if(systemTickComponents[i] != NULL)
00164             systemTickComponents[i]->systemTick();
00165 }
00166 
00167 /**
00168   * Add a component to the array of system components. This component will then receive
00169   * periodic callbacks, once every tick period.
00170   *
00171   * @param component The component to add.
00172   *
00173   * @return MICROBIT_OK on success. MICROBIT_NO_RESOURCES is returned if the component array is full.
00174   *
00175   * @note The callback will be in interrupt context.
00176   */
00177 int system_timer_add_component(MicroBitComponent *component)
00178 {
00179     int i = 0;
00180 
00181     // If we haven't been initialized, bring up the timer with the default period.
00182     if (timer == NULL || ticker == NULL)
00183         system_timer_init(SYSTEM_TICK_PERIOD_MS);
00184 
00185     while(systemTickComponents[i] != NULL && i < MICROBIT_SYSTEM_COMPONENTS)
00186         i++;
00187 
00188     if(i == MICROBIT_SYSTEM_COMPONENTS)
00189         return MICROBIT_NO_RESOURCES;
00190 
00191     systemTickComponents[i] = component;
00192     return MICROBIT_OK;
00193 }
00194 
00195 /**
00196   * Remove a component from the array of system components. This component will no longer receive
00197   * periodic callbacks.
00198   *
00199   * @param component The component to remove.
00200   *
00201   * @return MICROBIT_OK on success. MICROBIT_INVALID_PARAMETER is returned if the given component has not been previously added.
00202   */
00203 int system_timer_remove_component(MicroBitComponent *component)
00204 {
00205     int i = 0;
00206 
00207     while(systemTickComponents[i] != component && i < MICROBIT_SYSTEM_COMPONENTS)
00208         i++;
00209 
00210     if(i == MICROBIT_SYSTEM_COMPONENTS)
00211         return MICROBIT_INVALID_PARAMETER;
00212 
00213     systemTickComponents[i] = NULL;
00214 
00215     return MICROBIT_OK;
00216 }