37
votes
Accepted
How do interrupts work on the Arduino Uno and similar boards?
TL;DR :
When writing an Interrupt Service Routine (ISR):
Keep it short
Don't use delay ()
Don't do serial prints
Make variables shared with the main code volatile
Variables shared with main code may ...
- 37.9k
20
votes
Accepted
Using millis() and micros() inside an interrupt routine
The other answers are very good, but I want to elaborate on how micros() works. It always reads the current hardware timer (possibly TCNT0) which is constantly being updated by the hardware (in fact, ...
- 37.9k
14
votes
Why the need to use the volatile keyword on global variables when handling interrupts in Arduino?
First, it's volatile not Volatile. I cover these concepts in my page about Interrupts however to avoid giving a link-only answer I'll repeat the relevant bits.
What are "volatile" variables?
...
- 37.9k
12
votes
Attach the Arduino ISR function to the class member
Interrupt Service Routine (ISR) outside a class
Let's consider a simple use of interrupts:
volatile bool switchChanged;
void switchPressed ()
{
switchChanged = true;
} // end of switchPressed
...
- 37.9k
9
votes
Accepted
How to properly use volatile variables in Arduino?
You need to learn about critical sections.
What is probably happening is that the variables are being changed by the interrupt routines mid-way through the calculations. Your 'fix' reduces the time ...
- 105k
9
votes
Using millis() and micros() inside an interrupt routine
It is not wrong to use millis() or micros() within an interrupt routine.
It is wrong to use them incorrectly.
The main thing here is that while you are in an interrupt routine "the clock isn't ...
- 105k
9
votes
Calling I2C functions inside an ISR
Here is an analogy for you to help you understand why using the IRQ is a good idea.
Imagine you are at a conference. There's hundreds of you in the audience, and you are in a question and answer ...
- 105k
9
votes
Accepted
What is the right way to query an I2C device from an interrupt service routine?
Just because a pin is called "interrupt" doesn't mean that you have to read it using an interrupt input. The INTx pins of the ADXL345 are simple "level" outputs. All the time there is an "interrupt" ...
- 105k
9
votes
Accepted
Alternative to polling interrupt flag from main loop?
If the task is pretty short and time sensitive, your best option is to
put it in the interrupt handler.
If the task is big and not too urgent (like: it could well wait for a
millisecond or so), your ...
- 42.2k
8
votes
Accepted
Sending serial data in an interrupt
You cannot use Serial inside an interrupt. Transmitting Serial relies on interrupts being available, and from inside an interrupt they aren't.
All Serial communication must be done from loop().
So ...
- 105k
8
votes
How to generate hardware interrupt in mpu6050 to wakeup arduino from SLEEP_MODE_PWR_DOWN mode?
Well, this code worked. In this code, MPU's INT PIN is Active Low so generates Ground on motion which is than connected to INT0 or arduino UNO pin 2 which generates interrupt and wakes UP the MCU
#...
- 307
7
votes
IR Receiver interrupt and arduino sleep mode
This is what I have managed to achieve ...
Library
IRLib - GitHub
Version 1.51 March 2015
Copyright 2013-2015 by Chris Young http://tech.cyborg5.com/irlib/
This library is a major rewrite ...
- 37.9k
7
votes
interrupting an interrupt
the timer will set the Timer Interrupt Flag (TIFR0 register)
The ISR will be called, and the flag will be cleared
you do some long calculations or something
the timer will match OCR0A, and set the ...
- 11.3k
7
votes
Accepted
Debouncing a button with interrupt
So, I grabbed a Mega and several pushbutton switches (one of which turned out to be a push-on, push-off, much to my bemusement), and ginned up a small Arduino program to illustrate an interrupt-driven ...
- 734
7
votes
Accepted
Pin Change Interrupt Flag timing on 1284P
When it is entered. The wording is slightly vague but I think "when the interrupt routine is executed" means the commencement of execution. Otherwise multiple pin-change interrupts could be ...
- 37.9k
6
votes
Using millis() and micros() inside an interrupt routine
The quoted phrase is not a warning, it is merely a statement about how things work.
There's nothing intrinsically wrong with using millis() or micros() within a properly-written interrupt routine.
...
- 8,830
6
votes
Accepted
Critical sections in Arduino, interrupt consuming data
Warning: I am not familiar with the ESP8266 hardware, and some of my
answers below may be only valid on the AVR architecture.
The simplest way to synchronize your main code with your interrupt
...
- 42.2k
6
votes
Accepted
Using a lot of interrupts on a single Arduino
On a Uno, all of the digital and analog pins can trigger a pin-change interrupt. That gives you 20 inputs straight away. The Mega also has pin change interrupts but not on all its pins. The pins that ...
- 37.9k
6
votes
Accepted
Arduino Interrupt example not working
I think you misunderstood this example: it is not expected to automatically blink!
The LED is suposed to change state at every change of level on pin 2. This supposes that you wired something (e.g. a ...
- 9,112
6
votes
Accepted
Which Arduinos support ATOMIC_BLOCK?
This answer covers: Which Arduinos support ATOMIC_BLOCK? And how can I duplicate this concept in C with __attribute__((__cleanup__(func_to_call_when_x_exits_scope))) and in C++ with class constructors ...
- 1,359
6
votes
Accepted
ATTiny13 Interrupt Issue
You would want your bool LED_STATE = false; to be volatile qualified like volatile bool LED_STATE = false; otherwise the compiler's optimizer may assume that the value cannot be changing between loads ...
- 5,008
6
votes
Accepted
Using interrupts as flags/latches without any ISR
The answer to your question is: yes, you can use an interrupt flag even
if the interrupt itself is disabled. The flag is raised whenever the
peripheral detects the relevant event. You can check it at ...
- 42.2k
5
votes
Accepted
Read RC receiver channels using Interrupt instead of PulseIn
Regarding the question, “Does PinChangeInt only work on digital pins?”, note that PCI's work on all the digital pins of an ATmega328, and on the first six analog pins. (32-pin '328s have eight analog ...
- 8,830
5
votes
Accepted
AVR timer overflow interrupt not working
You are misunderstanding what an overflow interrupt is. That is called when the timer overflows (ie. it reaches TOP which in the case of an 8-bit timer is 255). Since you are counting to 124 that will ...
- 37.9k
5
votes
Accepted
Managing 2 ultrasonic sensors without blocking the other
I strongly advice you to use interrupts and make sure the sensors are in a cylindrical cone in order to prevent interference to each others as much as possible.
Here is code snippet which can give ...
- 394
5
votes
Accepted
How to set the sampling frequency in Arduino without using a delay
Use the concept of blink without delay.
Instead of using delay() to set the timeout you use a timestamp and check micros() against that to see whether your interval has passed:
const unsigned long ...
- 3,267
5
votes
Constant ADC sampling rate on ESP8266 or ESP32
You have several options for controlling the sampling rate.
Software only
This is the simplest, and the previous answer got it almost right. Here
is my take:
const SAMPLE_INTERVAL = 500; // 500 ...
- 42.2k
5
votes
What is the right way to query an I2C device from an interrupt service routine?
Majenko's answer is useful — you can simply forego the use of interrupts for this and poll the pin directly in your main loop. Especially on AVR where the external pins are exposed as registers which ...
- 234
Only top scored, non community-wiki answers of a minimum length are eligible