Re: [avr-chat] newbie question

[Vincent Trouilliez]

On Wed, 29 Apr 2009 11:27:06 -0400
"King, Mike" <address@hidden> wrote:

> What problems will be solved by a watchdog circuit?

It recovers a system, by putting it a knonw state after it has gone out
of control, whatever the cause of the loss of control... For example,


> will it only protect against rare software bugs.

be it designer/software induced problems like bugs...


> Do CPU glitch?

... or hardware problems. Yes the CPU can misbehave, it's hardware and
sometimes they have design flaws, it designed by human beings after
all. But usually this is rare and well documented. Like the floating
point problems in the old Pentium, causing incorrect calculation in some
cases, which can of course cause the software, in turn, to misbehave.
I don't know if the AVR CPU's have known bugs, though... but the
experienced on this list will chime in I am sure ;-)

Another, more likely source of problems that could cause the
hardware (CPU or whatever peripheral on the chip) is interferences from
the environment. Like electronics used in satellites, which are
sensitive to the sun's activity. When the sun sends a burst of
radiation, the satellites must be tilted/turned around, to protect the
electronics.

So a watchdog timer can help recover the system by resetting it to a
known state, from mostly software bugs (designer's fault), or
environemental "aggressions" so to speak (not the designers
fault, assuming said interferences could not be foreseen from the
specified use cases of the products).

--
Vince