Diff: source/core/MicroBitSystemTimer.cpp

Revision:

1:8aa5cdb4ab67

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/source/core/MicroBitSystemTimer.cpp	Thu Apr 07 01:33:22 2016 +0100
@@ -0,0 +1,181 @@
+/*
+The MIT License (MIT)
+
+Copyright (c) 2016 British Broadcasting Corporation.
+This software is provided by Lancaster University by arrangement with the BBC.
+
+Permission is hereby granted, free of charge, to any person obtaining a
+copy of this software and associated documentation files (the "Software"),
+to deal in the Software without restriction, including without limitation
+the rights to use, copy, modify, merge, publish, distribute, sublicense,
+and/or sell copies of the Software, and to permit persons to whom the
+Software is furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in
+all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
+THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+DEALINGS IN THE SOFTWARE.
+*/
+
+/**
+  * Definitions for the MicroBit system timer.
+  *
+  * This module provides:
+  *
+  * 1) a concept of global system time since power up
+  * 2) a simple periodic multiplexing API for the underlying mbed implementation.
+  *
+  * The latter is useful to avoid costs associated with multiple mbed Ticker instances
+  * in microbit-dal components, as each incurs a significant additional RAM overhead (circa 80 bytes).
+  */
+#include "MicroBitConfig.h"
+#include "MicroBitSystemTimer.h"
+#include "ErrorNo.h"
+
+/*
+ * Time since power on. Measured in milliseconds.
+ * When stored as an unsigned long, this gives us approx 50 days between rollover, which is ample. :-)
+ */
+static unsigned long ticks = 0;
+static unsigned int tick_period = 0;
+
+// Array of components which are iterated during a system tick
+static MicroBitComponent* systemTickComponents[MICROBIT_SYSTEM_COMPONENTS];
+
+// Periodic callback interrupt
+static Ticker *timer = NULL;
+
+
+/**
+  * Initialises the system wide timer.
+  *
+  * This must be called before any components register to receive periodic periodic callbacks.
+  *
+  * @param timer_period The initial period between interrupts, in millseconds.
+  *
+  * @return MICROBIT_OK on success.
+  */
+int system_timer_init(int period)
+{
+    if (timer == NULL)
+        timer = new Ticker();
+
+    return system_timer_set_period(period);
+}
+
+/**
+  * Reconfigures the system wide timer to the given period in milliseconds.
+  *
+  * @param period the new period of the timer in milliseconds
+  *
+  * @return MICROBIT_OK on success. MICROBIT_INVALID_PARAMETER is returned if period < 1
+  */
+int system_timer_set_period(int period)
+{
+    if (period < 1)
+        return MICROBIT_INVALID_PARAMETER;
+
+    // If a timer is already running, ensure it is disabled before reconfiguring.
+    if (tick_period)
+        timer->detach();
+
+	// register a period callback to drive the scheduler and any other registered components.
+    tick_period = period;
+    timer->attach_us(system_timer_tick, period * 1000);
+
+    return MICROBIT_OK;
+}
+
+/**
+  * Accessor to obtain the current tick period in milliseconds
+  *
+  * @return the current tick period in milliseconds
+  */
+int system_timer_get_period()
+{
+    return tick_period;
+}
+
+/**
+  * Determines the time since the device was powered on.
+  *
+  * @return the current time since power on in milliseconds
+  */
+unsigned long system_timer_current_time()
+{
+    return ticks;
+}
+
+/**
+  * Timer callback. Called from interrupt context, once per period.
+  *
+  * Simply checks to determine if any fibers blocked on the sleep queue need to be woken up
+  * and made runnable.
+  */
+void system_timer_tick()
+{
+    // increment our real-time counter.
+    ticks += system_timer_get_period();
+
+    // Update any components registered for a callback
+    for(int i = 0; i < MICROBIT_SYSTEM_COMPONENTS; i++)
+        if(systemTickComponents[i] != NULL)
+            systemTickComponents[i]->systemTick();
+}
+
+/**
+  * Add a component to the array of system components. This component will then receive
+  * periodic callbacks, once every tick period.
+  *
+  * @param component The component to add.
+  *
+  * @return MICROBIT_OK on success. MICROBIT_NO_RESOURCES is returned if the component array is full.
+  *
+  * @note The callback will be in interrupt context.
+  */
+int system_timer_add_component(MicroBitComponent *component)
+{
+    int i = 0;
+
+    // If we haven't been initialized, bring up the timer with the default period.
+    if (timer == NULL)
+        system_timer_init(SYSTEM_TICK_PERIOD_MS);
+
+    while(systemTickComponents[i] != NULL && i < MICROBIT_SYSTEM_COMPONENTS)
+        i++;
+
+    if(i == MICROBIT_SYSTEM_COMPONENTS)
+        return MICROBIT_NO_RESOURCES;
+
+    systemTickComponents[i] = component;
+    return MICROBIT_OK;
+}
+
+/**
+  * Remove a component from the array of system components. This component will no longer receive
+  * periodic callbacks.
+  *
+  * @param component The component to remove.
+  *
+  * @return MICROBIT_OK on success. MICROBIT_INVALID_PARAMETER is returned if the given component has not been previously added.
+  */
+int system_timer_remove_component(MicroBitComponent *component)
+{
+    int i = 0;
+
+    while(systemTickComponents[i] != component && i < MICROBIT_SYSTEM_COMPONENTS)
+        i++;
+
+    if(i == MICROBIT_SYSTEM_COMPONENTS)
+        return MICROBIT_INVALID_PARAMETER;
+
+    systemTickComponents[i] = NULL;
+
+    return MICROBIT_OK;
+}