Arduino Software Interrupts

In this tutorial, we’ll discuss Arduino Software Interrupts and how to generate a software interrupt (trap) in Arduino. We’ll implement an Arduino Software Interrupt Example project to test what we’ll learn throughout this tutorial. Without further ado, let’s get right into it!

Table of Contents

1. Software Interrupts
2. Arduino Software Interrupts
3. Arduino Software Interrupt Example
4. Wrap Up

Software Interrupts

Software interrupts are interrupt signals that can be fired with specific software instructions. Some microcontrollers support native software interrupt instructions while others don’t have dedicated assembly instructions for the CPU to get an interrupt from the software.

Other techniques can be implemented to programmatically enforce an interrupt to the CPU within your software even if it doesn’t have a soft interrupt instruction. This of course requires some workarounds but it’s not that hard to do in general.

A software interrupt can be referred to as a Trap as well. Which is a technique to signal the CPU within the software to change the mode, throw an error, indicate an arithmetic error, or signal the OS.

Arduino Software Interrupts

It’s stated clearly in the Arduino UNO’s Atmega328p datasheet that it doesn’t have a dedicated assembly instruction to trigger a software-generated interrupt signal. But as we’ve stated earlier, we can still implement some workarounds to fire software-generated interrupt signals.

One technique to generate a software interrupt is clearly stated in the datasheet itself. Which is to enable any external interrupt pin (IRQ) and set it as an output pin. Writing to any pin of these will trigger an interrupt, and that’s how we get a software-generated interrupt even if it’s not supported by the microcontroller.

Arduino Software Interrupt Example

In this example project, we’ll test Arduino Software Interrupts. And here is how we’re going to do it.

First of all, we’ll use the INT0 (IO pin2) as an interrupt signal source but will trigger it from the software and will set it as an output pin. It’s not going to be connected to the push button or anything.

The push button input, however, is going to be connected to an IO pin8 that we’ll set as an input pin. Whenever the push button is pressed we’ll debounce it, once a click is confirmed, we’ll send a pulse (LOW->HIGH, RISING) to the output pin (INT0) which is going to trigger an interrupt event.

In the ISR handler for INT0 interrupt, we’ll toggle an output LED. I know, it’s not very intuitive but it’s still a valid test to verify the concept and make sure everything behaves as expected.

Wiring

Here is the wiring diagram for this example showing how to connect the LED output, and the push button to the input pin (pin8). And note that the INT0 (pin2) is set as an output pin and left unconnected.

Arduino Software Interrupt Example Code

Here is the full code listing for this Arduino Software Interrupt Example.

Code Explanation

We first need to define the IO pins to be used for the LED output & push button input (pin8). The (INT0 external interrupt pin = IO pin2) will be used in output mode to generate the software interrupt.

INT0_ISR()

This is the ISR handler function for the INT0 external interrupt in which we’ll only do a LED toggle action. For each RISING edge on the external interrupt pin, the CPU will execute this ISR function which will toggle the output LED.

The RISING edge on the INT0 pin will come from software in the loop() function, therefore the INT0_ISR handler function is the software interrupt handler.

setup()

in the setup() function, we’ll initialize the IO pins to be used as input & output using the pinMode() function to set their modes.

Then we’ll enable the external interrupt for the INT0 (pin2) using the attachInterrupt() function & set it to trigger on RISING edge events only.

loop()

in the loop() function, we’ll read the push button on the input pin8 and debounce it. Once a click is confirmed, we’ll send a LOW->HIGH pulse on the output INT0 pin to trigger an interrupt event from the software at the same moment when a button click is confirmed.

If you want to learn more about the Arduino button debouncing technique used in this example, and all other possible hardware & software button debouncing techniques, check out the tutorial below which presents everything you need to know about button debouncing in one place.

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Arduino Button Debouncing Techniques

This article will provide you with more in-depth information about Arduino button debouncing techniques both hardware & software methods. With a lot of code examples & circuit diagrams.

Wrap Up

To conclude this short tutorial, we’ll highlight the fact that Arduino Software Interrupts can be generated using other hardware interrupt sources like (external IRQ pins INTx or PCINTx). Because there are no special software interrupt instructions in the Arduino’s Atmega328p microcontroller’s instruction set. But all in all, it’s still doable and the example provided in this tutorial is basically how you can also do it.

If you’re just getting started with Arduino, you need to check out the Arduino Getting Started [Ultimate Guide] here.

And follow this Arduino Series of Tutorials to learn more about Arduino Programming.

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Getting Started With Arduino [Ultimate Guide]

This is the ultimate guide for getting started with Arduino for beginners. It’ll help you learn the Arduino fundamentals for Hardware & Software and understand the basics required to accelerate your learning journey with Arduino Programming.

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Arduino Interrupts Tutorial

This is the complete Arduino Interrupts Tutorial. It’ll provide you with more in-depth information about interrupts in general and specifically in Arduino, how it works, how to write efficient ISR handlers, and other tips & tricks.