IRJET- FPGA Implementation of an Improved Watchdog Timer for Safety-Critical Applications

International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056
Volume: 06 Issue: 03 | Mar 2019 www.irjet.net p-ISSN: 2395-0072
© 2019, IRJET | Impact Factor value: 7.211 | ISO 9001:2008 Certified Journal | Page 2218
FPGA Implementation of an Improved Watchdog Timer for
Safety-Critical Applications
A. Trephena Patricia1, E. Abinaya2, S. Harika3, P. Jasmine Florence Hebciba4, C. Sumathi5
1Professor, Dept. of ECE, Panimalar Engineering College, Poonamalle, TamilNadu, India.
2,3,4,5UG students, Dept. of ECE, Panimalar Engineering College, Poonamalle, TamilNadu, India.
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Abstract - Embedded systems that are employed in safety
critical applications require highest reliability. External
watchdog timers are used in such systems to automatically
handle and recover from operation time related failures.
Most of the available external watchdog timers use
additional circuitry to adjust their timeout periods and
provide only limited features in terms of their functionality.
This paper describes the architecture and design of an
improved configurable watchdog timer that can be
employed in safety-critical applications. Several fault
detection mechanisms are built into the watchdog, which
adds to its robustness. The functionality and operations are
rather general and it can be used to monitor the operations
of any processor based real-time system. This paper also
discusses the implementation of the proposed watchdog
timer in a Field Programmable Gate Array (FPGA). This
allows the design to be easily adaptable to different
applications, while reducing the overall system cost. The
effectiveness of the proposed watchdog timer to detect and
respond to faults is first studied by analyzing the simulation
results. Thus after designing the watchdog it is implemented
in ATM and verified. The design is validated in a real-time
hardware by injecting faults through the software while the
processor is executing.
1. INTRODUCTION
A watchdog timer is an electronic timer that is
used to detect and recover from computer malfunctions.
Watchdog timers are commonly found in embedded
systems and other computer-controlled equipment where
humans cannot easily access the equipment or would be
unable to react to faults in a timely manner. Watchdog
timers may also be used when running un-trusted code in
a sandbox, to limit the CPU time available to the code and
thus prevent some types of denial-of-service attacks.
During ordinary operation, the computer automatically
resets the watchdog timer to prevent it from timing out.
The timeout signal is used to represent corrective action
or actions.
1.1 EXISTING WATCHDOG TIMER:
In the existing system, a watchdog timer with no
windowed watchdog is executed. The input is directly sent
into the memory, from the memory instructions are
processed into the processor, this watchdog will not detect
the fault immediately. If there is any error occurrence in
between them, it will sequentially wait for its time to
trigger the CPU that error has occurred. It is totally
dependent on the CPU. Then after CPU, getting the error
information it will reset the whole process. It is stated as
slow watchdog fault mechanism. The time it takes to reach
the error mechanism to rectify is more than the proposed
system. Since it is not clock independent, this sequential
watchdog is a failure to embedded system. It is rectified
during this proposed system.
2. PROPOSED SYSTEM:
An effective watchdog should be able to detect all
abnormal software modes and bring the system back to a
known state. It should have its own clock and should be
capable of providing a hardware reset on timeout to all the
peripherals. The watchdog timer proposed in this paper
operates independently of the processor and uses a
dedicated clock for its functions. A fail flag is raised when
the watchdog timer expires and after a fixed amount of
time from raising the flag, a reset is triggered. The time in-
between can be used by the software to store valuable
debugging information to a non-volatile medium.

2.1 WATCHDOG TIMER IMPLEMENTATION IN FPGA:
The design is clocked by its SYSCLK input, which is
independent of the processor clock. The possible sets of
window lengths are arrived based on the application and
hard-coded in the design. These values can be selected by
writing to the appropriate bits in the configuration
register - SWLEN for the service window and FWLEN for
the frame window - after power-on. In order to change the
window lengths, the software will have to perform two
successive writes to this register with data 0xAAAA and
0x5555. Subsequent to writing the first pattern the second
one must be written within 10 μs, after which the software
gets a 10 μs period to modify the length configuration
fields. If these timings are not strictly met, writes to these
bits will remain disabled. The service window is started
when a high-to-low transition is detected on the INIT
signal. The service window uses a derived clock (SWCLK)
that is much slower than the SYSCLK. The slower clock
helps in reducing the number of comparators required,
thus minimizing the resource utilization in FPGA. The
service window has an offset up/down counter that are
clocked by the SYSCLK, and a main counter that runs at
SWCLK. When the watchdog is correctly serviced, the
counters in the service window stop immediately and the
frame window starts. The frame window also uses a
derived slower clock (FWCLK) for its operations. It has an
offset up/down counter and a main counter with
functionalities similar to that of the service window. The
offset up counter here finds the offset between the
termination of the service window and the next rising
edge FWCLK. The frame window counters reset when a
watchdog service operation occurs within the next service
window duration, before the frame window expires
2.2 PROPOSED BLOCK DIAGRAM WITH FAULT
INJECTION BLOCK
The random numbers generated are injected into the
program counter at random periods of time. A random
pulse is driven from a second PN sequence generator. This
pulse controls a multiplexer whose output is connected to
the Program counter. The inputs are either an incrementer
or the random generator. At all times the incrementer is
selected as this is the normal operation of the system.
Simultaneously the watchdog timer is running and a
counter records the number of times the watchdog is able
to detect the injected faults.
3. IMPLEMENTATION OF WATCHDOG IN SPACE
LAUNCH VEHICLE
The Space Launch System (SLS) is an American
Space Shuttle-derived super heavy-lift expendable launch
vehicle. It is part of NASA's deep space exploration plans
including a crewed mission to Mars. SLS follows the
cancellation of the Constellation program, and is to replace
the retired Space Shuttle. The NASA Authorization Act of
2010 envisions the transformation of the Constellation
program's Ares I and Ares V vehicle designs into a single
launch vehicle usable for both crew and cargo, similar to
the Ares IV concept.
Maintaining of space launch vehicle is the most
important parameter to be fixed .if there is any parameter
not checked or not built; it leads to large loss of money and
time. Thus our watchdog timers will do this job in a
perfect way.
In our existing system, all the parameters are
checked all at a time and if there is any fault in checking of
temperature, pressure and heat explosion, then these
parameters are made with some terminal value, checked
with the parameters pre-recorded, thus leading to
watchdog fault if there is an overflow value range.
Similarly in our proposed system, we find an efficient
way to check our parameters individually, thus leading to
windowed watchdog timer. Each window goes on
checking with each parameter, thus leading to wdfail in
each stage.

3.1 EXISTING SYSTEM
3.2 PROPOSED SYSTEM
OUTPUT
FAULT INJECTION BLOCK WATCHDOG TIMMER
If input and the program counter values updated in
register goes to service window then there is a fault. Thus
wdfail=1, rstout=1.
EXISTING SYSTEM APPLICATION IMPLEMENTATION
If parameter of temperature, pressure and heat values
does not exceed the limit so there is no error in watchdog.
Thus wdfail=0.

PROPOSED SYSTEM APPLICATION IMPLEMENTATION
If rstout, it goes back to the original initial value of space
launch vehicle.
FPGA OUTPUT
CONCLUSION
A good watchdog mechanism requires careful
consideration of both software and hardware. It also
requires careful consideration of what action to take when
the failure is detected. When you design with watchdog
hardware, make sure you decide early on exactly how you
intend to make best use of it, and you will reap the intend
benefits of a more robust system.
ACKNOWLEDGEMENT
We would like to express our special thanks of
gratitude to all my teachers as well as our principal who
gave us the golden opportunity to do this wonderful
project on this topic.
REFERENCES
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[2] V. B. Prasad, “Fault tolerant digital systems,” IEEE
Potentials, vol. 8, no. 1, pp. 17–21, Feb. 1989.
[3] J. Beningo, “A review of watchdog architectures and
their application to Cubesats,” Apr. 2010.
[4] A. Mahmood and E. J. McCluskey, “Concurrent error
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[5] B. Straka, “Implementing a microcontroller watchdog
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[6] J. Ganssle, “Great watchdogs,” V-1.2, The Ganssle
Group, updated January 2004, 2004.
[7] E. Schlaepfer, “Comparison of internal and external
watchdog timers application note,” Maxim Integrated
Products, 2008.
[8] P. Garcia, K. Compton, M. Schulte, E. Blem, and W. Fu,
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[9] G. C. Giaconia, A. Di Stefano, and G. Capponi, “FPGA-
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[10] A. M. El-Attar and G. Fahmy, “An improved watchdog
timer to enhance imaging system reliability in the
presence of soft errors,” in Signal Processing and
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