Electronics > Microcontrollers

Does Arduino have software interrupts?

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I got myself an Arduino and plan to do something with it ... as soon as I can resolve a few things first.

Many decades ago I used to program 6502 in assembler and the 6502 had interrupts which were HW pins which would interrupt the program and launch a separate routine. This was useful for dealing with infrequent and irregular events like keypresses, etc.

Do modern microcontrollers, especially Arduino, have something similar?

Suppose I want to use a keyboard for input; can I use interrupts or do I have to poll the keyboard all the time?

The way I understand it is that the "sketch" has an initialization part, which runs once at startup, and a main part which runs and repeats endlessly after that.

If there exist interrupts, where would the code go?

For ATmega328:
- hardware interrupts: yes
- software interrupts: no
Interrupts are handled by ISRs (function tied to a specific interrupt source).

Arduino is not a specific thing - it is an ecosystem of things. When it comes to hardware, there are multiple boards with very different MCUs, so you have to be specific.

Their sketch solution is based on two callbacks that are called from the initialization code added by the framework. You can implement other methods that you then call and if you want to implement an ISR, you will need to implement that in a separate function.

Now, the bigger question is why you want software interrupts in your Arduino code. I fail to see the point of using such things in that ecosystem.

OK, thanks. I have the Elegoo UNO R3 which I understand is an exact clone of the Arduino Uno and totally compatible.

ELEGOO UNO R3 Board ATmega328P with USB Cable(Arduino-Compatible) for Arduino

and also
ELEGOO Nano Board CH 340/ATmega+328P Without USB Cable, Compatible with Arduino Nano V3.0 (Nano x 3 Without Cable)

I gather the answer is that it does have HW interrupts but I guess my question is more about where the interrupt handling routine goes.

We have the main loop repeating over and over so we do not want to put the interrupt routine there. Or is it that I finish the main program by placing a jump to the beginning and after that I place the interrupt routine(s)? that way the interrupt routine(s) would never execute in the normal flow of the program.

How is the Interrupt routine identified as such?

Sorry but I am just not familiar with how the sketch program is structured.

A good start would be the datasheet for the microcontroller that whatever type of Arduino hardware you're using has.

When using the Arduinio IDE its a runtime thing that will use up a few resources (like timer0, and by default the USART on the Arduino uno - Atmega328).  But you can still just write bare-metal C in the IDE, and using the interrupts as you would in any other GCC application.  I often do kind of half in half - use the IDE, the bootloader, and a few built-in functions, but for the most part just write my own drivers for other hardware.  For just testing things or one-shot set ups, the built-in libraries are very handy - albeit can be unoptimised and buggy - but they are free so if it doesn't do something you want, write you're own, or fork then make a pull request to the libraries git.

There are of course many libraries that can help, but that all sits ontop of GCC so you don't have to use nay of the built-in libraries if you don't want to. 


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