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Loopless / low power examples.
A set of examples that demonstrate basic use of timers, interrupts, and tasks. Based on and tested on the nRF52840, but also compiles on the nRF52832 -- although you'll need an external button there.
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Diff for: ‎libraries/Bluefruit52Lib/examples/LowPower/Blink2_loopless/Blink2_loopless.ino

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/*
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Blink_loopless
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Created 2019-05-03
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by Pol Van Aubel
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Turns on an LED on for one second, then off for one second, repeatedly.
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This example is based on the original Blink sketch. The Adafruit nRF52* boards
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are more advanced than "normal" Arduinos, however, and come with freeRTOS
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and proper task management. This blink sketch demonstrates the use of two
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SoftwareTimers to perform two repetitive delayed tasks at different frequencies
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without using the energy that a continuously running loop() function has.
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AdaFruit's nRF-boards have multiple on-board LEDs you can control. These are
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addressable using the LED_RED, LED_BLUE, LED_BUILTIN and LED_CONN definitions.
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These take care to use the correct LED pin regardless of which board is used.
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If you want to know what pin the on-board LED is connected to on your model,
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check the Technical Specs of your board on https://www.adafruit.com/ or the
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board's variant.h at
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https://github.com/adafruit/Adafruit_nRF52_Arduino/tree/master/variants
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Based on the original Blink, the code of which is in the public domain.
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*/
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#include <Arduino.h>
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// Create the two SoftwareTimers we're going to use.
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SoftwareTimer bluetimer, redtimer;
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void setup()
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{
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// LED_RED & LED_BLUE are already initialized as outputs.
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// Initialize the timers at .75 seconds for blue, and 1 second for red.
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bluetimer.begin(750, bluetoggle);
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redtimer.begin(1000, redtoggle);
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bluetimer.start();
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redtimer.start();
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suspendLoop();
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}
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void loop(void) { }
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/**
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* Toggle led1 every 1 second
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*/
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void redtoggle(TimerHandle_t _handle)
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{
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digitalToggle(LED_RED); // Toggle LED
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}
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/**
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* Toggle led1 every 0.5 second
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*/
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void bluetoggle(TimerHandle_t _handle)
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{
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digitalToggle(LED_BLUE); // Toggle LED
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}

Diff for: ‎libraries/Bluefruit52Lib/examples/LowPower/Blink_loopless/Blink_loopless.ino

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/*
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Blink_loopless
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Created 2019-05-03
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by Pol Van Aubel
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Turns on an LED on for one second, then off for one second, repeatedly.
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This example is based on the original Blink sketch. The Adafruit nRF52* boards
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are more advanced than "normal" Arduinos, however, and come with freeRTOS
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and proper task management. This blink sketch demonstrates the use of
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SoftwareTimer to perform a repetitive delayed task without using the energy
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that a continuously running loop() function has.
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AdaFruit's nRF-boards have multiple on-board LEDs you can control. These are
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addressable using the LED_RED, LED_BLUE, LED_BUILTIN and LED_CONN definitions.
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These take care to use the correct LED pin regardless of which board is used.
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If you want to know what pin the on-board LED is connected to on your model,
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check the Technical Specs of your board on https://www.adafruit.com/ or the
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board's variant.h at
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https://github.com/adafruit/Adafruit_nRF52_Arduino/tree/master/variants
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Based on the original Blink, the code of which is in the public domain.
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*/
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// Create a SoftwareTimer that will drive our LED.
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SoftwareTimer led_timer;
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// the setup function runs once when you press reset or power the board
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void setup(void) {
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// initialize digital pin LED_BUILTIN as an output.
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pinMode(LED_RED, OUTPUT);
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// Set up a repeating timer that fires every half second (500ms) to toggle the LED.
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led_timer.begin(500, timer_callback);
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led_timer.start();
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// Since loop() is empty, suspend its task so that the system never runs it
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// and can go to sleep properly.
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suspendLoop();
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}
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void timer_callback(TimerHandle_t _handle) {
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digitalToggle(LED_RED); // toggle the red LED
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}
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// the loop function is empty and should never run.
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void loop(void) { }

Diff for: ‎libraries/Bluefruit52Lib/examples/LowPower/Button_interrupt/Button_interrupt.ino

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/*
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Button_interrupt
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Created 2019-05-04
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by Pol Van Aubel
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Uses an interrupt to listen for a button input. On the nRF52840, it can listen
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on pin 7 to the UserSW. On other boards, an external switch needs to be provided.
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The Adafruit nRF52* boards are more advanced than "normal" Arduinos and come
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with freeRTOS, interrupts available on every pin, and proper task management.
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This button sketch demonstrates the use of interrupts to act on an input such
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as a switch, without having to poll it in a continuously scanning loop() function.
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Even though human button presses are slow, and therefore unlikely to be missed
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using a scanning loop, the interrupt technique allows the board to go into sleep
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mode while waiting for an input, thereby saving a lot of energy.
17+
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AdaFruit's nRF-boards have multiple on-board LEDs you can control. These are
19+
addressable using the LED_RED, LED_BLUE, LED_BUILTIN and LED_CONN definitions.
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These take care to use the correct LED pin regardless of which board is used.
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If you want to know what pin the on-board LED is connected to on your model,
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check the Technical Specs of your board on https://www.adafruit.com/ or the
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board's variant.h at
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https://github.com/adafruit/Adafruit_nRF52_Arduino/tree/master/variants
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This code is licensed under CC0, effectively putting it in the Public Domain
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where possible.
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*/
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// On the nRF52840, pin 7 is the UserSW/DFU switch.
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int interruptPin = 7;
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// the setup function runs once when you press reset or power the board
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void setup(void) {
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pinMode(LED_RED, OUTPUT);
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pinMode(interruptPin, INPUT_PULLUP); // Configure the switch pin as an input with internal pull-up register enabled.
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// Configure it to call switch_callback if the switch pin transitions from HIGH to LOW, i.e. when it is pressed.
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// On the nRF52840, RISING and CHANGE are also valid options. Depending on your platform, LOW may also be available.
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attachInterrupt(interruptPin, switch_callback, FALLING);
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// Since loop() is empty, suspend its task so that the system never runs it
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// and can go to sleep properly.
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suspendLoop();
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}
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// the loop function is empty and should never run.
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void loop(void) { }
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// The switch_callback function is the function we attached to the interrupt on line 42.
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// This is known as an Interrupt Service Routine, or ISR.
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// It gets run every time the interrupt fires, in the interrupt context. Nothing else
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// happens while this is running. Therefore, it should be fast and simple.
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// In particular, it should never block, nor do Serial communication or use the Bluefruit API.
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// There are a few freeRTOS functions specifically designed to be run from an ISR.
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// If you need a longer ISR, other examples show how to do this.
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void switch_callback(void) {
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digitalToggle(LED_RED); // toggle the red LED
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// You may notice that the LED does not reliably turn on on one press of the switch,
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// then off on the next. This is likely due to a phenomenon physical switches exhibit called "bounce".
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// Effectively this means that the pin goes through multiple transitions of HIGH to LOW,
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// back to HIGH, to LOW again, for a single press of the button.
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// Some debouncing techniques using interrupts are shown in another example.
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}

Diff for: ‎libraries/Bluefruit52Lib/examples/LowPower/Button_interrupt_ada_callback/Button_interrupt_ada_callback.ino

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/*
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Button_interrupt_ada_callback
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Created 2019-05-04
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by Pol Van Aubel
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Uses an interrupt to listen for a button input. On the nRF52840, it can listen
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on pin 7 to the UserSW. On other boards, an external switch needs to be provided.
9+
10+
The Adafruit nRF52* boards are more advanced than "normal" Arduinos and come
11+
with freeRTOS, interrupts available on every pin, and proper task management.
12+
This button sketch demonstrates the use of interrupts to act on an input such
13+
as a switch, without having to poll it in a continuously scanning loop() function.
14+
Even though human button presses are slow, and therefore unlikely to be missed
15+
using a scanning loop, the interrupt technique allows the board to go into sleep
16+
mode while waiting for an input, thereby saving a lot of energy.
17+
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However, because interrupts need to be fast, you must not do Serial communication
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or long tasks directly in an ISR. This is where deferred ISRs come in. However,
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deferred ISRs cannot have a single time-critical component. By using
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ada_callback_fromISR, you can run a fast time-critical component in a normal
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ISR, and then queue up a callback to process the rest.
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AdaFruit's nRF-boards have multiple on-board LEDs you can control. These are
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addressable using the LED_RED, LED_BLUE, LED_BUILTIN and LED_CONN definitions.
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These take care to use the correct LED pin regardless of which board is used.
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If you want to know what pin the on-board LED is connected to on your model,
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check the Technical Specs of your board on https://www.adafruit.com/ or the
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board's variant.h at
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https://github.com/adafruit/Adafruit_nRF52_Arduino/tree/master/variants
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This code is licensed under CC0, effectively putting it in the Public Domain
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where possible.
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*/
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// On the nRF52840, pin 7 is the UserSW/DFU switch.
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int interruptPin = 7;
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// Because this variable is modified inside a non-deferred ISR, and used outside it,
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// it must be declared volatile to ensure that the most recently written value is
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// always used.
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volatile int numinterrupts;
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// the setup function runs once when you press reset or power the board
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void setup(void) {
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Serial.begin(115200); // Not required on the nRF52840 with native USB.
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while (!Serial) { // Stalls the nRF52840 until the USB serial console has been opened on the host PC.
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delay(10);
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}
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Serial.println("Press the button!");
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Serial.flush(); // Because this sketch does nothing else, it will go to sleep rather than send the
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// entire Serial buffer to the host PC. So, use Serial.flush() to make sure it does that
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// before allowing it to sleep.
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pinMode(LED_RED, OUTPUT);
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pinMode(interruptPin, INPUT_PULLUP); // Configure the switch pin as an input with internal pull-up register enabled.
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// Configure it to call switch_callback if the switch pin transitions from HIGH to LOW, i.e. when it is pressed.
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// On the nRF52840, RISING and CHANGE are also valid options. Depending on your platform, LOW may also be available.
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attachInterrupt(interruptPin, switch_isr, FALLING);
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// Since loop() is empty, suspend its task so that the system never runs it
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// and can go to sleep properly.
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suspendLoop();
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}
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// the loop function is empty and should never run.
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void loop(void) { }
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// The switch_isr function is the function we attached to the interrupt on line 63.
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// This is known as an Interrupt Service Routine, or ISR.
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// It gets run every time the interrupt fires, in the interrupt context. Nothing else
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// happens while this is running. Therefore, it should be fast and simple.
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// In particular, it should never block, nor do Serial communication or use the Bluefruit API.
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// There are a few freeRTOS functions specifically designed to be run from an ISR.
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void switch_isr(void) {
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// Do short time-critical processing (setting flags, queueing up tasks, etc) here.
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digitalToggle(LED_RED);
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++numinterrupts;
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ada_callback_fromISR(NULL, 0, switch_isr_callback); // Queue up a task with no extra variables and no arguments.
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// Every single interrupt is serviced, because internally, a
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// queue is used.
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}
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// The switch_isr_callback function is the function we set up as the ada_callback on line 84.
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// It gets run once for every interrupt that switch_isr ran for, but with no guarantees about
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// when that happens. However, the advantage is you have the full range of Serial, Bluefruit,
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// and freeRTOS API to use now.
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// Bear in mind, however, that if this function takes longer to run than the average time between
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// interrupts, at some point your ada_callback_queue will overflow. For that scenario, consider
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// batch-processing interrupts by using direct-to-task notifications.
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void switch_isr_callback(void) {
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Serial.println("Interrupt serviced!");
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Serial.print("The number of interrupts received at this point was ");
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Serial.println(numinterrupts);
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Serial.flush(); // Because this sketch does nothing else, it will go to sleep rather than send the
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// entire Serial buffer to the host PC. However, here, Serial.flush() doesn't seem
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// to work either. Maybe something to do with the task context?
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}

Diff for: ‎libraries/Bluefruit52Lib/examples/LowPower/Button_interrupt_deferred/Button_interrupt_deferred.ino

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/*
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Button_interrupt_deferred
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Created 2019-05-04
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by Pol Van Aubel
6+
7+
Uses an interrupt to listen for a button input. On the nRF52840, it can listen
8+
on pin 7 to the UserSW. On other boards, an external switch needs to be provided.
9+
10+
The Adafruit nRF52* boards are more advanced than "normal" Arduinos and come
11+
with freeRTOS, interrupts available on every pin, and proper task management.
12+
This button sketch demonstrates the use of interrupts to act on an input such
13+
as a switch, without having to poll it in a continuously scanning loop() function.
14+
Even though human button presses are slow, and therefore unlikely to be missed
15+
using a scanning loop, the interrupt technique allows the board to go into sleep
16+
mode while waiting for an input, thereby saving a lot of energy.
17+
18+
However, because interrupts need to be fast, you must not do Serial communication
19+
or long tasks directly in an ISR. This is where deferred ISRs come in.
20+
21+
AdaFruit's nRF-boards have multiple on-board LEDs you can control. These are
22+
addressable using the LED_RED, LED_BLUE, LED_BUILTIN and LED_CONN definitions.
23+
These take care to use the correct LED pin regardless of which board is used.
24+
If you want to know what pin the on-board LED is connected to on your model,
25+
check the Technical Specs of your board on https://www.adafruit.com/ or the
26+
board's variant.h at
27+
https://github.com/adafruit/Adafruit_nRF52_Arduino/tree/master/variants
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This code is licensed under CC0, effectively putting it in the Public Domain
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where possible.
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*/
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// On the nRF52840, pin 7 is the UserSW/DFU switch.
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int interruptPin = 7;
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// the setup function runs once when you press reset or power the board
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void setup(void) {
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Serial.begin(115200); // Not required on the nRF52840 with native USB.
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while (!Serial) { // Stalls the nRF52840 until the USB serial console has been opened on the host PC.
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delay(10);
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}
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Serial.println("Press the button!");
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pinMode(LED_RED, OUTPUT);
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pinMode(interruptPin, INPUT_PULLUP); // Configure the switch pin as an input with internal pull-up register enabled.
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// Configure it to call switch_callback if the switch pin transitions from HIGH to LOW, i.e. when it is pressed.
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// On the nRF52840, RISING and CHANGE are also valid options. Depending on your platform, LOW may also be available.
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// The ISR_DEFERRED flag ensures that the interrupt is serviced by a scheduled operating system task.
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// What this means is that the ISR is allowed to perform slow functionality, including Serial communication,
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// using the Bluefruit API, and the entire freeRTOS API rather than just the *FromISR functions.
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// Use this if your interrupt servicing is not time-critical.
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attachInterrupt(interruptPin, switch_deferred, ISR_DEFERRED | FALLING);
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// Since loop() is empty, suspend its task so that the system never runs it
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// and can go to sleep properly.
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suspendLoop();
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}
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// the loop function is empty and should never run.
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void loop(void) { }
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// The switch_deferred function is the function we attached to the interrupt on line 56.
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// This is known as an Interrupt Service Routine, or ISR.
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// Because it is a deferred ISR, it is not guaranteed to run immediately after the interrupt
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// happens. However, the advantage is you have the full range of Serial, Bluefruit,
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// and freeRTOS API to use now.
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void switch_deferred(void) {
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digitalToggle(LED_RED);
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Serial.println("Interrupt serviced!");
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Serial.flush(); // Because this sketch does nothing else, it will go to sleep rather than send the
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// entire Serial buffer to the host PC. So, use Serial.flush() to make sure it does that
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// before allowing it to sleep.
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// You may notice that you receive multiple messages per press of the switch,
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// This is likely due to a phenomenon physical switches exhibit called "bounce".
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// Effectively this means that the pin goes through multiple transitions of HIGH to LOW,
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// back to HIGH, to LOW again, for a single press of the button.
82+
// Some debouncing techniques using interrupts are shown in another example.
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}

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