Breaking New Ground in Chip Reliability

It seems like only yesterday LANs were a niche technology used exclusively in large, technology-oriented organizations. Today, they are just about everywhere - in offices, schools, and even homes. Several things are responsible for this widespread acceptance but none so influential as the advances made in VLSI components (or chips). The heart of every LAN, chips are now small and cheap, and can contain vast amounts of intelligence.

Designing and manufacturing VLSI components is a complicated task.

"QNX reduced our development time by close to 30 percent"

Typically used in high-performance systems, these chips demand extreme reliability. Consequently, before they can be commercially released, they require rigorous testing in various real-life situations.

Digital Semiconductor built an aggressively high-performance environment for this type of testing - in record time. A QNX-based system, it allowed us to introduce the DECchip 21440 to the market as the first of its class and, as a result, grab considerable marketshare. In fact, the number of ports reached the one million mark within months of its release.

Chip basics
The DECchip 21440 is the first chip in a family of multiport VLSI components specially designed for networking hubs. It features eight intelligent ports that can each function within a hub. It contains advanced logic for communicating with an external CPU and advanced bus-control logic. It also provides a variety of information about network behavior.

The design of the 21440 was first outlined in sketches by a team of architects and then defined in detailed diagrams of the chip's blocks by engineers. The resulting model was subjected to several months of testing, modifications, and bug fixes. Once the model stabilized and no new problems were found, a small number of prototypes were manufactured. These prototypes were then tested through system validation (SV).

Critical challenges
Because VLSI components are typically used in high-performance systems, an effective SV environment is critical to test a prototype and, perhaps more importantly, to provide the necessary information to debug it. Over and above the typical challenges - including tight deadlines and a conservative budget - we were faced with creating an SV environment that would:

• generate complex traffic patterns similar to those found in real networks
• process high-speed LAN data
• support automatic testing so that a small number of people could check a large number of tests
• test a maximum number of the chip's features

The final criterion was our biggest worry. An undetected bug could cause a lot of damage to us, our customers, and eventually the end user.

Reliability required
In order to meet our system design requirements, we decided on several basic criteria. First and foremost, we needed a high-performance operating system that would produce and monitor high-speed traffic. Second, we needed a platform that would readily support distributed processing since the SV environment demanded several closely synchronized systems. Third, we needed support for hardware-software interfaces. And finally, we needed reliability - implementing a critical test in an unreliable environment made little sense.

Choice OS
We debated long and hard about the design of our SV environment with much emphasis on which OS to choose. We decided on QNX for the above reasons and several more:

• modular OS design
• easy programmability - especially of hardware devices
• built-in connectivity
• standards compliance and Unix-like look and feel

We liked the fact that we could place high-performance modules where needed without compromising existing OS components and that we didn't have to use components we didn't need. We also appreciated the way the transparent connectivity of QNX made it unnecessary to build special layers for communicating between different machines. And, of course, we liked the short learning curve with a POSIX-compliant and Unix-like API.

Well-connected
Our QNX-based system validation environment consisted of several PCs linked together and a dedicated test board to house the 21440. The test board was connected to a test control machine - the controller - through a local PCI bus.

The environment required two networks. The first, a control network that used low-speed Ethernet, connected the controller to all other machines - or stations - using a DECchip 21040-based adapter with standard QNX drivers and built-in transparent QNX networking. The second, a test network that used Ethernet or Fast Ethernet, connected the test board to all stations using DECchip 21140-based adapters. The standard QNX networking stack was removed and specially designed drivers were implemented to control local adapters.The controller defined scripts and descriptions, distributed information to all stations, and set the 21440 in the desired mode of operation. It then synchronized the system and gave the start signal. The stations simulated real-life network traffic patterns and checked the 21440's behavior. At the end of each test, the stations processed the data (typically tens of megabytes) through the distributed network.

SV success story
The SV environment was implemented over the course of several months and was quickly put to work in actual testing. Although it was complex and high-performing, it took a relatively short time to stabilize. By all accounts, the SV environment was a success. The performance and realtime capabilities of QNX made it possible to achieve an extremely high-performance environment, which, in turn, made it possible to thoroughly test the 21440 before releasing it to market. What's more, the modular design and built-in components of QNX reduced our development time by close to 30 percent. We not only met a tight schedule, we did so with limited HR and financial resources at our disposal.

Because we were able to significantly reduce our time to market, the 21440 was the first of its class to be commercially available and achieved considerable marketshare as a result.

The sweet hereafter
Although the 21440 is already being sold, our QNX-based system validation environment is still used whenever new versions are introduced or problems creep up. In fact, it is now being modified and adapted to test the other new members of our family of multiport VLSI components. And, since the growth rate of the networking industry in the last several years has exceeded that of the PC industry, we know our QNX-based SV environment will serve us well for years to come.