Getting Started

Chapter 7: Microcontroller Interrupts and Timers

dog ar the page before closing the book. Then

e and when the call is finished and you’ve put out the fire in

ga refer to the desecrations to your book and go right back to

an interrupt causes the microcontroller to stop

sufficient data so that later it can get back to what it was

, and when

using the

r

ome particularly pernicious

ger from memory and since

opped by an

f the integer before returning control to the part

ding the integer which then gets the second byte of the

ger l be wrong because it will be made half from the pre-

rrupt value and half from the post-interrupt value. The crazy making

is that the interrupt can happen at any time, maybe only very

ly d p and then locks up

kind of bug in your pacemaker. You

ven g interrupts before reading variables that can be

nged by interrupts then enabling them after you’ve got the correct number.

g some fairly intense code based on the Butterfly

ick. If you compare the software used in this

you might think I stole some of it. And you’d be

rect. That is one of the central principles of software engineering: if it ain’t

if it is nailed down, get a crowbar and rip it up. It’s

e stupid to reinvent the wheel by trying to

you have perfectly good code already

ilable. There are only two reasons to write stuff you can steal, one is that you

s to avoid a lawsuit - if the software doesn’t

can be used, then it is copyrighted. Hopefully, I won’t get

to the line you were reading and -e
you a
our

nswer the phon
y rage, you can
where you left off your reading.

From the hardware perspective
what it is doing, store
doing, look to see which interrupt happened, run the interrupt code
finished restore the machine to its state before the interrupt occurred
previously sto ed data.

Interrupts are great, but they provide an avenue for s
bugs. For example when your code is reading an inte
an integer is made of two bytes it gets the first byte, then is st
interrupt that changes the value o
o ode that was rea

. The integer wil

f the c
inte
inte
debugging problem
rare uring the integer read. Your system can run like a cham
for no apparent reason. You don’t want this
pre t this bug by disablin
cha

We’ll study interrupts by usin
software used to read the joyst
example to the Butterfly software
cor
nailed down - steal it. Heck,
also called ‘code reuse’ and you’d b
write something from scratch when
ava
want to learn by doing, and the other i
specifically state that it
sued.