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Embedded Programming and Robotics

Learn about Arduino interrupts, a hardware event that can make your program far more responsive. Understand the overview, available interrupts, interrupt service routines, and how to write a sample program using interrupts.

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Embedded Programming and Robotics

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  1. Embedded Programming and Robotics Lesson 11 Arduino Interrupts Arduino Interrupts

  2. Interrupts Overview • An interrupt is a hardware event • The processor stops what it was doing and calls the code at a specific location, determined by the type of interrupt • Further interrupts are disabled • The Interrupt Service Routine (ISR) must save state, then restore it upon return (Arduino does this for you) • Timing is critical; ISRs must execute very quickly Arduino Interrupts

  3. Interrupts Overview • Most Arduino programs poll various sensors, and the Arduino can do this quickly • This is costly because the program must read the device whether data is present or not • Interrupts can make your program far more responsive Arduino Interrupts

  4. Available Interrupts • On the Arduino Uno we’re using, only pins 2 and 3 can cause interrupts • Thus you can have two different service routines for two different sensors • The Mega has six available interrupts Arduino Interrupts

  5. Interrupt Service Routines • Use the following function to link a service routine to an interrupt: attachInterrupt(interrupt, ISR, mode) • Interrupt is either 0 or 1, which is pin 2 or 3 on the Uno • ISR is the name of the interrupt service routine • Mode is one of the following: • LOW to trigger the interrupt whenever the pin is low, • CHANGE to trigger the interrupt whenever the pin changes value • RISING to trigger when the pin goes from low to high, • FALLING for when the pin goes from high to low. Arduino Interrupts

  6. Interrupt Service Routines • ISRs take no parameters and return no values • Variables modified by ISRs should be declared as volatile volatile intmscount; attachInterrupt(0, increment, RISING); Arduino Interrupts

  7. Interrupt Service Routines void increment() { mscount++; } Arduino Interrupts

  8. Sample Program • People can perceive events that take longer than a specific duration • Write a program that turns on an LED for a variable number of milliseconds, then off for 2 seconds. Start at 1 millisecond • Write an interrupt service routine that, when a switch is pressed, increments the number of milliseconds by 1 • Press the switch until you notice that the LED blinks • If you have time, connect the LCD panel to show the “on” time so you don’t have to count button presses Arduino Interrupts

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