Skip to Main Content
Programming Embedded Systems, 2nd Edition
book

Programming Embedded Systems, 2nd Edition

by Michael Barr, Anthony Massa
October 2006
Intermediate to advanced content levelIntermediate to advanced
336 pages
9h 13m
English
O'Reilly Media, Inc.
Content preview from Programming Embedded Systems, 2nd Edition

Interrupt Service Routine

Let’s take a closer look at the ISR. The ISR is the function called when a particular interrupt occurs. Its central purpose is to process the interrupt and then return control to the main program. Typically, ISR functions have no arguments passed into them; they can never return a value.

In order to keep the impact of interrupts on the execution of the main program to a minimum, it is important to keep interrupt routines short. If additional processing is necessary for a particular interrupt, it is better to do this outside of the ISR. Keeping ISRs short also aids in ISR debug, which can be difficult. When it is done by a specific function, completion of the interrupt handling outside the ISR is called a deferred service routine (DSR).

Regardless of the specific processing required by the ISR, the ISR is responsible for doing the following things:

Saving the processor context

Because the ISR and main program use the same processor registers, it is the responsibility of the ISR to save the processor’s registers before beginning any processing of the interrupt. The processor context consists of the instruction pointer, registers, and any flags. Some processors perform this step automatically.

Acknowledging the interrupt

The ISR must clear the existing interrupt, which is done either in the peripheral that generated the interrupt, in the interrupt controller, or both.

Restoring the processor context

After interrupt processing, in order to resume the main program, ...

Become an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month,
and much more.
Start your free trial

You might also like

Programming with STM32: Getting Started with the Nucleo Board and C/C++

Programming with STM32: Getting Started with the Nucleo Board and C/C++

Donald Norris

Publisher Resources

ISBN: 0596009836Supplemental ContentErrata Page