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Dependencies: BLE_API mbed-dev-bin nRF51822
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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 unsigned long ticks = 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 *timer = NULL; 00053 00054 00055 /** 00056 * Initialises the system wide timer. 00057 * 00058 * This must be called before any components register to receive periodic periodic callbacks. 00059 * 00060 * @param timer_period The initial period between interrupts, in millseconds. 00061 * 00062 * @return MICROBIT_OK on success. 00063 */ 00064 int system_timer_init(int period) 00065 { 00066 if (timer == NULL) 00067 timer = new Ticker(); 00068 00069 return system_timer_set_period(period); 00070 } 00071 00072 /** 00073 * Reconfigures the system wide timer to the given period in milliseconds. 00074 * 00075 * @param period the new period of the timer in milliseconds 00076 * 00077 * @return MICROBIT_OK on success. MICROBIT_INVALID_PARAMETER is returned if period < 1 00078 */ 00079 int system_timer_set_period(int period) 00080 { 00081 if (period < 1) 00082 return MICROBIT_INVALID_PARAMETER; 00083 00084 // If a timer is already running, ensure it is disabled before reconfiguring. 00085 if (tick_period) 00086 timer->detach(); 00087 00088 // register a period callback to drive the scheduler and any other registered components. 00089 tick_period = period; 00090 timer->attach_us(system_timer_tick, period * 1000); 00091 00092 return MICROBIT_OK; 00093 } 00094 00095 /** 00096 * Accessor to obtain the current tick period in milliseconds 00097 * 00098 * @return the current tick period in milliseconds 00099 */ 00100 int system_timer_get_period() 00101 { 00102 return tick_period; 00103 } 00104 00105 /** 00106 * Determines the time since the device was powered on. 00107 * 00108 * @return the current time since power on in milliseconds 00109 */ 00110 unsigned long system_timer_current_time() 00111 { 00112 return ticks; 00113 } 00114 00115 /** 00116 * Timer callback. Called from interrupt context, once per period. 00117 * 00118 * Simply checks to determine if any fibers blocked on the sleep queue need to be woken up 00119 * and made runnable. 00120 */ 00121 void system_timer_tick() 00122 { 00123 // increment our real-time counter. 00124 ticks += system_timer_get_period(); 00125 00126 // Update any components registered for a callback 00127 for(int i = 0; i < MICROBIT_SYSTEM_COMPONENTS; i++) 00128 if(systemTickComponents[i] != NULL) 00129 systemTickComponents[i]->systemTick(); 00130 } 00131 00132 /** 00133 * Add a component to the array of system components. This component will then receive 00134 * periodic callbacks, once every tick period. 00135 * 00136 * @param component The component to add. 00137 * 00138 * @return MICROBIT_OK on success. MICROBIT_NO_RESOURCES is returned if the component array is full. 00139 * 00140 * @note The callback will be in interrupt context. 00141 */ 00142 int system_timer_add_component(MicroBitComponent *component) 00143 { 00144 int i = 0; 00145 00146 // If we haven't been initialized, bring up the timer with the default period. 00147 if (timer == NULL) 00148 system_timer_init(SYSTEM_TICK_PERIOD_MS); 00149 00150 while(systemTickComponents[i] != NULL && i < MICROBIT_SYSTEM_COMPONENTS) 00151 i++; 00152 00153 if(i == MICROBIT_SYSTEM_COMPONENTS) 00154 return MICROBIT_NO_RESOURCES; 00155 00156 systemTickComponents[i] = component; 00157 return MICROBIT_OK; 00158 } 00159 00160 /** 00161 * Remove a component from the array of system components. This component will no longer receive 00162 * periodic callbacks. 00163 * 00164 * @param component The component to remove. 00165 * 00166 * @return MICROBIT_OK on success. MICROBIT_INVALID_PARAMETER is returned if the given component has not been previously added. 00167 */ 00168 int system_timer_remove_component(MicroBitComponent *component) 00169 { 00170 int i = 0; 00171 00172 while(systemTickComponents[i] != component && i < MICROBIT_SYSTEM_COMPONENTS) 00173 i++; 00174 00175 if(i == MICROBIT_SYSTEM_COMPONENTS) 00176 return MICROBIT_INVALID_PARAMETER; 00177 00178 systemTickComponents[i] = NULL; 00179 00180 return MICROBIT_OK; 00181 }
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