Testing embedded data buses and analog signals
Instrument makers help designers measure the bewildering array of analog and digital signals embedded processors, FPGAs, and application-specific custom and standard ICs can generate.
Rick Nelson, Chief Editor -- EDN, June 23, 2010
At A Glance
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Sidebar: Opportunity at the edge |
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Embedded computers are finding
their way into products ranging
from automobiles and aircraft to
mobile devices and tabletop consumer
appliances. Designers working in the
embedded market face many challenges
in selecting the right processor or microcontroller
and software. They must then
demonstrate that the product they design
works. If it doesn’t work, they need to pinpoint
the cause of failure and provide a fix.
To help designers accomplish that goal,
test-and-measurement companies are offering
a variety of instruments, including
oscilloscopes, logic analyzers, and protocol
analyzers. In addition, software companies
are making test-software suites that can
put a product through its paces and ensure
that it will meet customer expectations.The ESC (Embedded Systems Conference) Silicon Valley, which took place in San Jose, CA, in April, provided test-and-measurement companies an opportunity to highlight their offerings for the embeddedsystem market. Test-related products on display ranged from traditional oscilloscopes through logic analyzers, protocol analyzers, and software as vendors tried to attract customers who are designing processors, FPGAs, and other components into their embedded systems.
Tektronix showcased mixed-signal oscilloscopes at
ESC, presenting the results of a time-and-motion study
it sponsored that demonstrated how long it takes engineers
to find runts and glitches when debugging designs.
According to the study, users perform typical debugging
tasks 53% faster when using Tektronix scopes,
such as the MSO4000 mixed-signal oscilloscope (Figure 1), than with competitors’ versions.
Serial and parallel buses
“We know from our own research that 60% of oscilloscope users are working with serial buses today and 50% are working with parallel buses,” says Gina Maria Bonini, technical-marketing manager at Tektronix. With users’ emphasis on digital debugging, Tektronix wanted to know how efficiently its scopes could support customers compared with competitors’ scopes selling for $19,000 to $21,000, she adds. Toward that end, Tektronix commissioned Hansa GCR to conduct in-person interviews with 47 experienced oscilloscope users, asking them to complete the same debugging task.
“This directional research indicated that users were able to find runts and glitches in a signal twice as fast with the Tektronix oscilloscope compared to the Agilent and LeCroy scopes,” says Andrea Eaker, senior research consultant at Hansa GCR. “Users also found the automated search feature and available triggers particularly useful in completing these tasks, and Tektronix received the highest satisfaction ratings overall.”
The study asked the participants to set up each oscilloscope to monitor for glitches and runts, set up a trigger and capture a runt, and search the waveform to locate all runt instances. According to Bonini, the ability to quickly perform those steps helps users pinpoint signalintegrity problems that relate to timing errors, bus-contention issues, metastability, setup-and-hold violations, and various physical-layer issues involving termination and other problems.
Bonini attributes the Tektronix scopes’ performance in the study to the company’s digital-phosphor technology, which enables the capture of 50,000 waveforms/ sec. “With the digital-phosphor technology, we overlay waveform after waveform to try to duplicate the analogscope experience so that users can see when there are anomalies in a signal,” she says. The MSO4000 also has an automated- search feature that is useful for long-record oscilloscopes that can perform 10 million-point acquisitions, representing 10,000 screens of data. With the MSO4000, a user can set up a runt trigger and leave the oscilloscope running overnight or over a weekend, looking for metastability or other problems.
Embedded-test tools
Dan Monopoli and William Driver, product-marketing managers at LeCroy, describe the types of instruments and capabilities embedded-system designers—versus designers in other areas—are looking for. LeCroy customers are in two broad camps: those who attend ESC and those who attend DesignCon. Although both Monopoli and Driver attended ESC, the show tends to be the domain of Monopoli, who is primarily responsible for products that operate as fast as 1 GHz. DesignCon, on the other hand, is more the domain of Driver, who is primarily responsible for products in the 1- to 6-GHz range.
According to Monopoli, customers at ESC are looking for instruments that can handle decoding for I2C (inter-integrated- circuit), SPI (serial-peripheral- interface), and UART (universalasynchronous- transmitter/receiver) signals. In contrast, DesignCon attendees are looking for high-bandwidth scopes that can help investigate signal-integrity issues on high-speed buses, such as USB 3 and PCIe Generation 3. Design- Con attendees are early adopters who are bringing up new silicon or perhaps don’t even have silicon yet but are preparing to make measurements when it does arrive.
LeCroy exhibited 6- and 30-GHz scopes at ESC to demonstrate the company’s broad product lineup, but Driver says that he answered more questions about Monopoli’s product lineup than about his own. Having high-end instruments at ESC gave the company the chance to demonstrate the consistent options, capabilities, and interfaces across the full lineup of instruments, Driver explains.
Monopoli says that this year’s ESC Silicon Valley attendees were not looking for high bandwidth or tremendous memory depth but rather extensive measurement capabilities that would enable them to handle mixed-signal circuits as well as I2C, SPI, and, increasingly, CAN (controller-area-network) buses, which are finding use beyond traditional automotive applications. Prospective customers also want all these capabilities at an attractive price that will enable them to get prompt purchase approval. A hot topic at Design-Con one year, he says, will turn out to be a hot topic at ESC a few years later as prices for new technology fall to a point at which it can serve in embedded- system applications (see sidebar “Opportunity at the edge”).
At ESC, LeCroy introduced its Arb-Studio AWGs (arbitrary-waveform generators) and LogicStudio 16 logic
analyzer. The ArbStudio AWGs (Figure 2a) generate signals as fast as 125
MHz and include PWM (pulse-widthmodulation)
capabilities. The software
interface that controls the hardware
simplifies waveform creation with a
navigation tree that allows easy access
to all channels.
The ArbStudio series includes four models: two- and four-channel versions with analog waveform capabilities plus two- and four-channel versions offering a combination of analog waveform and digital pattern-generation capabilities that Monopoli describes as the AWG versions of mixed-signal oscilloscopes. The four-channel models have an expansion port that allows you to connect as many as eight units. All models have a 125-MHz bandwidth, 1G-sample/sec maximum sample rate, 2 million-point/channel memory, and 16-bit resolution. The instruments support both true arbitrary and DDS (direct-digital-synthesis) technologies. ArbStudio software runs on an external PC. According to Monopoli, LeCroy chose ESC for the introduction because it well fits the embedded- system-test niche with an attractive less-than-$5000 price. Prices for the models range from $2490 to $4990.
LeCroy also debuted at ESC its LogicStudio
16 (Figure 2b), which brings
logic-analyzer functions to a PC, providing
16 channels with a sample rate
of 1G sample/sec and maximum input
frequency as great as 100 MHz. Logic-Studio 16 software provides a dynamic
waveform display with an intuitive
user interface. Tools for digital debugging
include timing cursors, zooming
and panning functions, a persistence
display, and a history mode that can
replay old data captures. LogicStudio
supports protocol analysis for I2C, SPI,
and UART interfaces. It can trigger on
specific bus addresses or data packets.
With a $990 price, the LogicStudio 16
is neither the most expensive nor the
least expensive USB logic analyzer in
its class, says Monopoli. A key benefit
is that LogicStudio provides a communication
link to LeCroy’s WaveJet oscilloscope,
thereby turning a PC in to a
mixed-signal debugging environment.
Web reliance
One company conspicuous in its absence from ESC was Agilent Technologies, the largest test-andmeasurement company. Joel Woodward, senior product manager for Agilent’s oscilloscope group, explains that Agilent last exhibited products a couple of years ago when it introduced the InfiniiVision 7000. However, says Woodward, who also is responsible for the midrange Infiniium models that target the embedded-system market, the company has found more costeffective ways—primarily, the Internet— to reach prospective customers. He cites the increasing tendency to build Web servers into instruments, enabling prospective customers to remotely testdrive them and get a full demonstration without attending a trade show.
If Agilent had exhibited products,
Woodward says, he would have demonstrated
the company’s logic analyzers
and oscilloscopes as they apply to three
technologies, each of which applies to
multiple markets. The company would
also have highlighted its probing technology
(Figure 3). After all, Agilent’s
instruments can’t measure signals if
there’s no way to access them on the
board under test.
Agilent would choose to highlight its technology that employs FPGAs, which have grown to a $3 billion market from the niche market they constituted in the early 1990s. Woodward says that FPGAs are often the centerpieces of embedded designs for medical, consumer, industrial, aerospace and defense, and even mobile-computing markets. Agilent serves designers of embedded systems incorporating FPGAs by offering dynamic-probe technology that lets designers incrementally peer into FPGAs, seeing additional sets of signals with a few mouse clicks.
If Agilent had attended
ESC, it would also have addressed
memory and serial-bus
technologies. “DDR memory
has really taken hold in the
embedded market, and a lot of
embedded development teams
using DDR memory have
acute needs for validating and
debugging their memory solutions,”
Woodward says. These
products include oscilloscopes
and logic analyzers for physical-
and protocol-layer analysis.
He concurs with his counterparts
at LeCroy and Tektronix
on the ubiquity of serial
buses, such as lower-speed
buses I2C and SPI. High-speed
buses are also appearing in
embedded designs (Figure 4). Agilent
also offers approximately 20 protocolanalysis
products, many in conjunction
with its oscilloscopes.
Software approaches
Not all test products on exhibit at ESC were test instruments. For example, Kozio representatives were on hand to highlight the company’s software for design validation, manufacturing test, and in-field test. The company offers a suite of software tools for embedded systems. According to Joseph Skazinski, co-founder and chief business-development officer at the company, the software provides broad datapath coverage and standardized diagnostic tests across functional areas. It also supports fast, automatic troubleshooting, giving users maximum control. Skazinski says that customers can save $100,000 in test development and debugging costs per project and achieve a three-month reduction in time to market.
The Kozio suite helps PCB (printedcircuit- board) designers contend with increasingly complex boards. Skazinski cites Mentor Graphics figures showing that average board sizes have decreased over the last 15 years from 101 to 75 in.2. Component counts, however, have increased from 649 to 3399, component pins have increased from 4214 to 13,505, and the number of pin-to-pin connections has increased 5190 to 10,960. Meanwhile, designers are contending with tight schedules, limited resources, design and manufacturing silos, and the need to deal with remote teams.
For design validation, the tools support interactive hardware debugging, fault isolation, characterization, and regression testing. For manufacturing test, they support parallel test and IP (intellectual- property) protection, and contract manufacturers can adapt them. In the field, the tools support built-in selftest and diagnostics. The tools provide coverage of memory, data buses, user interfaces, displays, and cameras, as well as audio, networking, and wireless functions.
Kozio’s recent product introductions include an expansion of its Diagnostics Design Suite in-system diagnostics software to support the PowerPC 460GTx and 460 SX storage processors from Applied Micro Circuits. Kozio’s tool provides at-speed functional tests with interactive and automated interfaces. This year, the company announced support for the new OMAP (Open Multimedia Applications Platform) 4 from Texas Instruments.
If you are looking to embed
instrument capability into your
systems, you might consider the
line of board-level backplanes
that National Instruments introduced at ESC (Figure 5). The new
backplanes, previously available only as
part of NI’s PXI (PCI extensions for instrumentation)/CompactPCI (Peripheral
Component Interconnect) and PXIe
(PXI Express) chassis, allow OEMs to
create their own custom, rugged enclosures
that can accommodate PXI, PXIe,
CompactPCI, and CompactPCIe (PCI
Express) modules.
The more than 10 new 3U and 6U backplanes offer four to 18 slots. Engineers can design custom installations and enclosures around the backplanes and integrate more than 1500 PXI modules, including data-acquisition cards; FPGA-based I/O modules; highend instruments, such as signal generators and RF-signal analyzers; and a variety of bus-interface modules, including serial, MIL-STD (military-standard)-1553, IEEE 1588, Profibus, and DeviceNet versions.
Designers can use the NI LabView graphical-system-design platform to design, prototype, and deploy all aspects of their systems, in keeping with what Casey Weltzin, LabView real-time product manager at NI, describes as a focus on letting domain experts in robotics, medical, and energy industries, for example, take a large role in embedded-system designs.
Embedded test’s future
You can expect instrumentation offerings to continue to evolve as vendors develop strategies to help their customers contend with embedded-system designs, but don’t expect the demise of any instruments or the emergence of drastically new ones. The industry has seen the decline of some classes of instrumentation. Agilent’s Woodward points out that board-level emulators, for example, have declined because you can get the functionality of a $30 emulator board for a nickel’s worth of onprocessor silicon.
The emergence of MSOs (mixed-signal oscilloscopes) might suggest that they will put logic analyzers on a path to follow board-level emulators, but vendors of both classes of instruments don’t expect that scenario to happen. Tektronix’s Bonini says that the logic analyzer will remain the tool of choice for logic designers who need to dig deep into protocol layers to troubleshoot designs with multiple buses. For logic-analyzer users who need to look at analog effects, Tektronix offers a multiplexer within its logic analyzers that can route signals to an oscilloscope without the inconvenience and loading effects of trying to attach two probes to a circuit node of interest.
Access to serial buses and instruments that can decode the bus protocols will become increasingly important to embedded- system test as circuitry becomes ever more complex. “As the many design blocks in embedded systems continue to get integrated into ever-moredense ICs, such as FPGAs, ASICs, and ASSPs [application-specific standard products], our experience has been that the serial-communications buses between blocks don’t disappear,” says Woodward. “Often, they are the only means of access for a design team to get information on what’s happening in its design.”
Increasingly, those buses will be highspeed, and you can expect a decrease in the time delay between when a bus represents a hot topic at DesignCon and when it’s a hot topic at ESC, as Monopoli describes. Woodward notes that the cost of high-seed serial SERDES (serializer/deserializer) buses isn’t that daunting. If you buy a modern FPGA, it is essentially free.
“People in the medical industry have embraced high-speed serial buses,” says Woodward. “In MRI [magnetic-resonance imaging], the buses can move large amounts of graphics data from one subsystem in a design to another subsystem. A lot of times, we think of embedded as a lagging industry, but embedded has wholeheartedly embraced the adoption of high-speed serial links. I think FPGAs are driving a big part of that. You’ll also find a number of ASSPs that have begun incorporating these high-speed transceivers that are also priced so that they work in the embedded market. The wonderful thing about the computer industry is it will drive the price of advanced technology down so it becomes feasible for embedded teams to implement them in their designs.”
You can reach Editor-in-Chief Rick Nelson at richard.nelson@cancom.com.
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