Interrupts, The Big Picture
Interrupts, The Big Picture
While many of you are already familiar with interrupts, they are so fundamental to embedded
systems that we wanted to briefly describe what they are all about.
From Wikipedia:
A hardware interrupt is an electronic alerting signal sent to the processor from an external device,
either a part of the [device, such as an internal peripheral] or an external peripheral.
In other words, the interrupt is a signal which notifies the CPU that an event has occurred. If the
interrupt is configured, the CPU will respond to it immediately – as described later in this chapter.
Polling vs Interrupts
In reality, though, there are two methods that events can be recognized by the processor. One is
called “Polling”; the other is what we just defined, “Interrupts”.
We start with a non-engineering analogy for these two methods. If you’ve ever taken a long family
vacation, you’ve probably dealt with the “Are we there yet” question. In fact, kids often ask it over-
and-over again. Eventually … the answer will be, “Yes, we’re there”. The alternative method is
when my spouse says, “Wake me up when we get there”.
Waiting for an Event: Family Vacation
Polling
Wake me up when we get there...
Interrupts
Both methods signal that we have arrived at our destination. In most cases, though, the use of
Interrupts tends to be much more efficient
. For example, in the case of the MSP430, we often
want to sleep the processor while waiting for an event. When the event happens and signals us
with an interrupt, we can wake up, handle the event and then return to sleep waiting for the next
event.
MSP430 Workshop - Interrupts 5 - 3
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