Interrupts

Question 1

What is the defintion of a task?

Answer 1

A distinct activity that is required to be performed

Question 2

What is an event triggered task?

Answer 2

This is a task that can occur at unpredictable times

Question 3

What is polling?

Answer 3

This is when you repeatedly check the status of an input to see if it changes

Question 4

What is the issue with polling?

Answer 4

It wastefully consumes power

Question 5

What is an edge triggered interrupt?

Answer 5

The interrupt is configured to detect a changing input (from HIGH to LOW or from LOW to HIGH).
Main execution is halted and only when the interrupt is triggered, a side execution is started and then when that is done the microcontroller halts and sleeps again.

Question 6

What is a hybrid aproach to get button input whilst sleeping the microcontroller?

Answer 6

> Combining interrupts and polling
The microcontroller halts and sleeps and the interrupt is triggered which changes a flag variable
After the flag variable is triggered the microcontroller wakes and resumes and then sees that the flag has changed and execute the required code before sleeping again

Question 7

What is a time triggered task?

Answer 7

This is when a timer triggers the interrupt

Question 8

What are the two types of time triggered interrupts?

Answer 8

Ticker = Triggers periodically
Timeout = To trigger once

Question 9

What are the two sleep modes? What is the difference?

Answer 9

sleep()
> System clock is stopped
> Saves dynamic power
> Peripherals continue on working and can generate interrupts
> Woken with timers, serial or external pin interrupt
deepsleep()
> System clock is stopped
> Peripherals and clocks power down
> Only woken using external pin interrupt

Question 10

How do you declare an event triggered interrupt in c++?

Answer 10

InterruptIn buttonA(PTC7);

Question 11

How do you structure an event triggered interrupt function and variable?

Answer 11

volitile int g_buttonA_flag = 0;
void buttonA_isr();

Question 12

How do you set a falling edge interrupt?

Answer 12

buttonA.fall(&buttonA_isr);

Question 13

What is the event triggered interrupt function?

Answer 13

void buttonA_isr()
{
    g_buttonA_flag = 1;
}

Question 14

How do you declare a ticker?

Answer 14

Ticker ticker;

just like an object

Question 15

How do you structure a ticker interrupt function and variable?

Answer 15

volitile int g_timer_flag = 0;
void timer_isr();

Question 16

How do you start a ticker?

Answer 16

ticker.attach(&timer_isr, 0.5);

Question 17

What is part of the ticker function?

Answer 17

void timer_isr()
{
    g_timer_flag = 1;
}

Question 18

How do you stop the ticker?

Answer 18

ticker.detach();