2008
Chapter-3 L15: "Embedded Systems - " , Raj Kamal,
Publs.: McGraw-Hill Education
1
DEVICES AND COMMUNICATION
BUSES FOR DEVICES NETWORK–
Lesson-15: Watchdog Timer
2008
Chapter-3 L15: "Embedded Systems - " , Raj Kamal,
Publs.: McGraw-Hill Education
2
Watchdog timer
λ A timing device such that it is set for a
preset time interval and an event must occur
during that interval else the device will
generate the timeout signal on failure to get
that event in the watched time interval.
λ On that event, the watchdog timer is
disabled to disable generation of timeout or
reset
λ Timeout may result in processor start a
service routine or start from beginning
2008
Chapter-3 L15: "Embedded Systems - " , Raj Kamal,
Publs.: McGraw-Hill Education
3
Example
• Assume that we anticipate that a set of tasks
must finish in 100 ms interval.
• The watchdog timer is disabled and stopped
by the program instruction in case the tasks
finish within 100 ms interval.
• In case task does not finish (not disabled by
the program instruction), watchdog timer
generates
interrupts after 100 ms and
executes a routine, which is programmed to
run because there is failure of finishing the
task in anticipated interval.
2008
Chapter-3 L15: "Embedded Systems - " , Raj Kamal,
Publs.: McGraw-Hill Education
4
Watchdog timer application
• An application in mobile phone is that
display
is off
in case no GUI
interaction
takes place within a
watched time interval.
• The interval is usually set at 15 s, 20 s,
25 s, 30 s in mobile phone.
• This saves power.
2008
Chapter-3 L15: "Embedded Systems - " , Raj Kamal,
Publs.: McGraw-Hill Education
5
Watchdog timer application
• An
application
in
temperature
controller is that if controller takes no
action to switch off the current within
preset watched time interval,
t