System Level Test

Why not use boundary scan throughout the entire system?

System_Test_Whitepaper.pdf  System Level Test article  Print this page Contact us Tip a colleague about this page

Boundary scan (IEEE 1149.1/JTAG) can be embedded into practically any system to enhance reliability while reducing operating and maintenance costs. The versatility of JTAG is especially important in mission-critical and high-performance applications in the telecom, server, and military/aerospace industries where high availability – “five 9s” or 99.999% availability or greater – is essential.


    For these and many other applications, boundary scan can be used to:
  • Remotely run structural diagnostics on boards, systems and backplanes
  • While the system is running, program complex programmable logic devices (CPLDs), field programmable gate arrays (FPGAs) and serial programmable read-only memories (PROMs) in the field
  • Reconfigure FPGAs for at-speed functional diagnostics in the field
  • Track firmware versions, serial numbers and other board characteristics
Reducing NFF
“Reliability often depends on imperfections that are not quite faults. For example, when ‘voids’ exceed 5% of the volume of a solder joint, when a whisker of conductive material extends more than 50% of the way across a gap between traces or when a spot is more than 13% out of true alignment, there is a high probability of failure after the product is in-service and subjected to thermal cycling or mechanical stresses.” - Test & Measurement World, April 2005.

NFF is a huge problem. It drives up warranty and out-of-warranty return costs, and its effects on the cost of field operations can be enormous. When a circuit board intermittently fails or it has a fault that functional diagnostics cannot detect, it will often be swapped and returned to the depot for repair. After re-certification testing, the board may be deployed again and again, causing additional failures and outages and deteriorating customer satisfaction.

Because boundary scan can test the structural integrity of a system in the field as part of initial installation or as an out-of-service troubleshooting test, it frequently spots problems that can not be detected by any other means.

Improving Reliability and Customer Satisfaction
Embedded JTAG can act as a secondary maintenance bus for remote systems. The device access of boundary scan can be used to remotely re-program CPLDs in the field, eliminating board swapping or dispatching a technician to connect a cable to the system to upgrade firmware. In effect, many on-site field repair trips can be completely eliminated. This can be a huge cost saving. And because boundary scan can still function even though a board’s processor is offline, it can be used to measure and report on voltages, temperature, and other parameters; retrieve and store firmware versions to hold all boards in a system to the same revision level, reducing possible system conflicts; and reconfigure an FPGA as a BIST controller to test peripherals at-speed and validate operating system and functional diagnostics performance.

Eliminating Costs for Manual Field Upgrades
System designers for “dark office” or “lights-out” equipment need to provide as much remote maintenance capability into these systems as possible. Whether in a data center or a remote installation in the desert, such systems must provide for intelligent self-healing diagnostics and firmware updating to reduce the technician’s time “behind the windshield” driving to the remote site for repair or upgrades. Consider that for a product that has 5,000 units deployed in the field, one upgrade may require four or more hours per unit; and if the technician’s loaded labor cost is $75/hour, this upgrade will cost $1.5 million. And that’s just one upgrade.

As device complexity goes up and product lifecycle costs become even more important, OEMs who adopt embedded boundary scan methodologies will continue to enjoy a competitive advantage. Over time virtually all complex hardware systems will employ this approach.