- Factored periodic timer funcitonality out of fiber scheduler and into a new SystemTimer module module. - Enapsulated "ticks" variable within SystemTimer module, with accessor funciton. - Added accessor/mutator functions to get and set the tick period. - Added a class wrapper to permit periodic callbacks to both C and C++ functions. - Updated all references in microbit-dal to use this refactored API.master
Joe Finney
7 years ago
parent
8a06a4e3be
commit
9218e647e0
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/**
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* Definitions for the MicroBit system timer.
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*
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* This module provides:
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*
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* 1) a concept of global system time since power up
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* 2) a simple periodic multiplexing API for the underlying mbed implementation.
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*
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* The latter is useful to avoid costs associated with multiple mbed Ticker instances
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* in microbit-dal components, as each incurs a significant additional RAM overhead (circa 80 bytes).
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*/
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#ifndef MICROBIT_SYSTEM_TIMER_H
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#define MICROBIT_SYSTEM_TIMER_H
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#include "mbed.h"
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#include "MicroBitConfig.h"
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#include "MicroBitComponent.h"
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/**
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* Initialises the system wide timer.
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* This must be called before any components register to receive periodic periodic callbacks.
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*
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* @param timer_period The initial period between interrupts, in millseconds.
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* @return MICROBIT_OK on success.
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*/
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int system_timer_init(int period);
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/*
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* Reconfigures the system wide timer to the given period in milliseconds.
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*
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* @param period the new period of the timer in milliseconds
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* @return MICROBIT_OK on success. MICROBIT_INVALID_PARAMETER is returned if period < 1
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*/
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int system_timer_set_period(int period);
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/*
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* Provides the current tick period in milliseconds
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* @return the current tick period in milliseconds
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*/
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int system_timer_get_period();
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/*
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* Determines the time since the device was powered on.
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* @return the current time since poweron in milliseconds
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*/
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unsigned long system_timer_current_time();
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/**
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* Timer callback. Called from interrupt context, once per period.
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* Simply checks to determine if any fibers blocked on the sleep queue need to be woken up
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* and made runnable.
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*/
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void system_timer_tick();
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/**
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* add a component to the array of system components. This component will then receive
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* period callbacks, once every tick period.
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*
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* @param component The component to add.
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* @return MICROBIT_OK on success. MICROBIT_NO_RESOURCES is returned if further components cannot be supported.
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*/
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int system_timer_add_component(MicroBitComponent *component);
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/**
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* remove a component from the array of system components. this component will no longer receive
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* period callbacks.
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* @param component The component to remove.
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* @return MICROBIT_OK on success. MICROBIT_INVALID_PARAMETER is returned if the given component has not been previous added.
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*/
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int system_timer_remove_component(MicroBitComponent *component);
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/**
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* A simple C/C++ wrapper to allow periodic callbacks to standard C functions transparently.
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*/
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class MicroBitSystemTimerCallback : MicroBitComponent
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{
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void (*fn)(void);
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/**
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* Creates an object that receives periodic callbacks from the system timer,
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* and, in turn, calls a plain C function as provided as a parameter.
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*/
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public:
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MicroBitSystemTimerCallback(void (*function)(void))
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{
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fn = function;
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system_timer_add_component(this);
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}
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void systemTick()
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{
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fn();
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}
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};
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#endif
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@ -0,0 +1,138 @@
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/**
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* Definitions for the MicroBit system timer.
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*
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* This module provides:
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*
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* 1) a concept of global system time since power up
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* 2) a simple periodic multiplexing API for the underlying mbed implementation.
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*
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* The latter is useful to avoid costs associated with multiple mbed Ticker instances
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* in microbit-dal components, as each incurs a significant additional RAM overhead (circa 80 bytes).
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*/
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#include "MicroBit.h"
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/*
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* Time since power on. Measured in milliseconds.
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* When stored as an unsigned long, this gives us approx 50 days between rollover, which is ample. :-)
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*/
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static unsigned long ticks = 0;
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static unsigned int tick_period = 0;
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// Array of components which are iterated during a system tick
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static MicroBitComponent* systemTickComponents[MICROBIT_SYSTEM_COMPONENTS];
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// Periodic callback interrupt
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static Ticker timer;
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/**
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* Initialises the system wide timer.
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* This must be called before any components register to receive periodic periodic callbacks.
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*
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* @param timer_period The initial period between interrupts, in millseconds.
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* @return MICROBIT_OK on success, or MICROBIT_INVALID_PARAMETER if period is illegal.
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*/
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int system_timer_init(int period)
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{
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return system_timer_set_period(period);
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}
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/*
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* Reconfigures the system wide timer to the given period in milliseconds.
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*
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* @param period the new period of the timer in milliseconds
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* @return MICROBIT_OK on success. MICROBIT_INVALID_PARAMETER is returned if period < 1
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*/
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int system_timer_set_period(int period)
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{
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if (period < 1)
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return MICROBIT_INVALID_PARAMETER;
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// If a timer is already running, ensure it is disabled before reconfiguring.
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if (tick_period)
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timer.detach();
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// register a period callback to drive the scheduler and any other registered components.
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tick_period = period;
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timer.attach_us(system_timer_tick, period * 1000);
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return MICROBIT_OK;
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}
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/*
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* Provides the current tick period in milliseconds
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* @return the current tick period in milliseconds
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*/
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int system_timer_get_period()
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{
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return tick_period;
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}
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/*
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* Determines the time since the device was powered on.
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* @return the current time since poweron in milliseconds
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*/
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unsigned long system_timer_current_time()
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{
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return ticks;
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}
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/**
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* Timer callback. Called from interrupt context, once per period.
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* Simply checks to determine if any fibers blocked on the sleep queue need to be woken up
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* and made runnable.
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*/
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void system_timer_tick()
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{
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// increment our real-time counter.
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ticks += system_timer_get_period();
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// Update any components registered for a callback
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for(int i = 0; i < MICROBIT_SYSTEM_COMPONENTS; i++)
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if(systemTickComponents[i] != NULL)
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systemTickComponents[i]->systemTick();
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}
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/**
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* Add a component to the array of system components. This component will then receive
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* period callbacks, once every tick period.
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*
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* @param component The component to add.
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* @return MICROBIT_OK on success. MICROBIT_NO_RESOURCES is returned if further components cannot be supported.
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*/
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int system_timer_add_component(MicroBitComponent *component)
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{
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int i = 0;
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while(systemTickComponents[i] != NULL && i < MICROBIT_SYSTEM_COMPONENTS)
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i++;
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if(i == MICROBIT_SYSTEM_COMPONENTS)
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return MICROBIT_NO_RESOURCES;
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systemTickComponents[i] = component;
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return MICROBIT_OK;
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}
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/**
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* remove a component from the array of system components. this component will no longer receive
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* period callbacks.
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* @param component The component to remove.
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* @return MICROBIT_OK on success. MICROBIT_INVALID_PARAMETER is returned if the given component has not been previous added.
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*/
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int system_timer_remove_component(MicroBitComponent *component)
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{
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int i = 0;
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while(systemTickComponents[i] != component && i < MICROBIT_SYSTEM_COMPONENTS)
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i++;
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if(i == MICROBIT_SYSTEM_COMPONENTS)
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return MICROBIT_INVALID_PARAMETER;
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systemTickComponents[i] = NULL;
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return MICROBIT_OK;
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}
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