In “Watchdogs redux,” columnist Jack Ganssle continues his longstanding campaign for the use of watch dog timers (WDTs) to safeguard the reliability of increasingly complex embedded systems. According to Jack: “a WDT is the last line of defense against product failure. Designed correctly, the system is guaranteed to recover from a crash; anything else may result in a ticked-off customer. Or loss of an expensive mission. Or, for the unfortunate users, injury and death.”
Witness to their importance in embedded systems, a search of Embedded.com’s online archive of articles results in several dozen contributions in which WDTs played a role similar to that of a nail in a horseshoe, the lack of which Shakespeare’s King Richard blamed for the loss of his kingdom.
Included here below are links to about a dozen of these articles on Embedded.com which reflect the range of systems in which WDTs are used. Of these some of my favorite Editor’s Top Picks include:
Introduction to Watchdog Timers
Need a watchdog for improved system fault tolerance?
Insulin pumps: design basics and tradeoffs
Embedding an IPMI platform management subsystem
I have also included a number of Jack’s previous columns on WDTs, including: “Watchdogs,” “Born to fail,” and “Li’l Bow Wow.”
Unfortunately, despite their ubiquity and importance in guaranteeing embedded system reliabile operation, it is Jack’s assessment that many WDTs were – and still are – poorly designed, to wit: “Many vendors are putting more thought into their WDT designs; some are doing a pretty good job. But we have a long way to go, and the wise developer will apply sound engineering practices to this often-neglected part of the system.“
What is your experience with watchdogs? How are you using them in your designs? What alternatives are you investigating? (Embedded.com Editor Bernard Cole, , 928-525-9087 )
Design How Tos
Introductionto Watchdog Timers
For those embedded systems that can't be constantly watchedby a human, watchdog timers may be the solution.
Needa watchdog for improved system fault tolerance?
Need a watchdog? This article outlines the requirements fora robust Watchdog and guidelines to be considered while designing this faulttolerant system monitor. Methods for refreshing a watchdog, write protectionmechanism, early detection of code runaway, and a self-test of the watchdogare described.
Howto get the most out of a single timer on an MCU
This article suggests a method to incorporate the functionalityof both an RTC and a PWM in a microcontroller equipped with only a singletimer.
Thecase for stand-alone reset timers in mobile devices
Stand-alone reset timers offer the most reliable resolutionto the 'white screen of death' problem in mobile devices.
Usingrequirements planning: Part 3 – Defining system timing
In this six part tutorial, Keith Curtis takes you step by stepthrough development of an embedded systems design requirements document fora seven digit electronic alarm clock. Part 3: Defining system timing requirement.
SafeguardMCU outputs against faults and errors
The reliable management of errors and faults is a priority fordesigners of automotive electronics.
Tipson building & debugging embedded designs
In a two part series, Jack Ganssle, editor of “Embedded Systems:World Class Designs,” passes on some tips about embedded systems design gainedfrom his experiences as both a designer and a manager of hardware and softwareprojects.
EMCBasics #2: Resets as critical circuits
Understand the EMC vulnerability of this ubiquitous circuitfunction, and what to do about it
Low-costcooperative multitasking, Part 2 – Building an MP3 Player
In the second part in a series, Ganesh Krishna looks at themethodologies for building the software for an MP3 player including designingtasks, inter task communication, prioritizing, etc. and how to build a systemthat integrates USB, a file system, LCD and capacitive touch sensing.
Insulinpumps: design basics and tradeoffs
This case study looks at the interplay between design goals,up-to-date components, subsystem issues, and regulatory requirements.
FaultMonitoring in Less-Than-Perfect Battery Management Systems
Understand the requirements for reliability and redundancy incritical battery-operated applications, and a how specific IC is designedto meet them
Embeddingan IPMI subsystem to monitor server system health
AMD’s James Edwards describes the implementation of an FPGA-basedopen source Intelligent Platform Management Interface subsystem to monitorthe health of server systems.
Multi-voltagesystems need tough supervisors
The original voltage supervisors met a simple need: monitorthe voltage that powered the system logic, and reset the processor followingpower-up or a low-voltage condition.
PSR/SSRmixed PWM controller keeps standby power under 10mW for portable device chargers
Fairchild Semiconductor developed the FAN302HL PWM controller forlow standby power charger applications. Incorporating mWSaver technology,the device features patented technologies that allow the FAN302HL to minimizestandby input power consumption to <10mW@230VAC, exceeding ENERGY STARProgram Requirements for Computers Version 5.0 efficiency standards.
WindRiver On-Board Program now enables hardware partners to create unique EmbeddedDevelopment Kits
Wind River's On-Board Program has been expanded to provide participatingcommercial off-the-shelf (COTS) processor board vendors with software tools,documentation and training to develop, test and validate their own uniqueEmbedded Development Kits.
STMicroelectronicslaunches STM32L ulra-low-power ARM Cortex-M3 MCU Series for Energy-Lite apps
STMicroelectronics has announced the extension of its 32-bit STM32Lseries of microcontrollers to include devices with memory densities of 256and 384 Kbytes, offering a Flash memory range from 32 up to 384 Kbytes forembedded applications.
News & Analysis
Calxeda gives a peek into its ARM server SoC
Calxeda is developing a quad-core Cortex A9 server SoC that consumes 5W including DRAM and embeds an interconnect supporting 120 SoCs in a 2U-sized chassis.
Analyst: Intel may miss Q1 sales target
Intel is in danger of missing the midpoint of its first quarter sales target range due to multiple signs of weak PC demand from the PC supply chain, according to a Wall Street analyst.