The nice thing about this is that if you change the microcontroller, e.g. In the Arduino world, you control this kind of interrupt via attachInterrupt(). For the ATmega328P, these are the interrupts INT0 and INT1. Virtually every microcontroller has interrupts that are triggered by an external event, such as a pin level change (HIGH/LOW, LOW/HIGH). Here is an overview of the interrupts of the ATmega328P (Arduino UNO, Nano, Pro Mini): Interrupts of the ATmega328P Which interrupts are available is hardware-specific. An example of this is the Timer0 overflow, which is used on AVR-based Arduino boards for the millis() function. In part, you use them without realizing it because the underlying code is implemented in libraries and macros. Microcontrollers use many different interrupts. When the trigger condition is met, the program jumps to the ISR, executes the instructions specified there, and jumps back to where it was interrupted:Īn ISR is somewhat similar to the time-out in certain ball sports, as the picture in the article is meant to suggest. But what if the program has to keep running because other tasks need to be done regularly? And what if processing these tasks takes longer than pressing the button? That’s where the interrupts are helpful.įor an interrupt, you need two things, namely a trigger and an action (Interrupt Service Routine = ISR). If a loop() pass is shorter than a button press takes, then you could insert the digitalRead() query without a blocking element.īoth may be acceptable in some circumstances.So you stop the program at this point until the button is pressed. You permanently query the button state, for example in a while loop.Whether the button was pressed could be queried with digitalRead(). ![]() Now imagine that, for example, an LED is to be switched on or off when a push button is pressed. one instruction (statement) is processed after the other. In programming, we are used to thinking sequentially, i.e. ATmega328P – Programming external interrupts on register level.Controlled suspension of interrupts with noInterrupts().Dealing with large volatile variables in ISRs.However, this has made this post quite lengthy, even in two parts.Īfter a general introduction, the first part deals with external interrupts. Maybe one or the other advanced reader will also find some new details. My motivation for writing my own contribution was to go a little deeper into some aspects. There are actually already more than enough articles about external interrupts on the net, and many of them are excellent. In addition, the programming of interrupts is quite hardware-specific. However, there are a number of stumbling blocks when using them. Interrupts can be used to elegantly overcome many challenges in programming Arduino boards or other microcontrollers.
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