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FlexRay Measurements

May 2007Page 1

FlexRay Presents New Challenges forFlexRay Presents New Challenges for

Oscilloscope MeasurementsOscilloscope Measurements

Presented by: Johnnie Hancock, Agilent Technologies

FlexRay Presents New Challenges for Oscilloscope Measurements

With the rapid adoption of the FlexRay communication bus in automobiles, embedded

hardware designers need to perform signal integrity measurements of their FlexRay-based

designs. The primary tool to verify proper signal fidelity and timing of signals is an

oscilloscope. Unfortunately, most oscilloscopes lack the required triggering and decoding

capabilities that the FlexRay protocol presents. The FlexRay protocol, which is a

deterministic bus based on a time-triggered technology presents new measurement

challenges not only for FlexRay designers, but also for oscilloscope vendors.

Since FlexRay will be employed into many safety-critical systems in the near future, such as

brake-by-wire, steer-by-wire, and collision-avoidance systems, it is critical that hardware

designers verify proper timing of transmitted frames relative to the specified FlexRay timing

schedule. In addition, unlike CAN technology where it is common for error frames to occur

due to arbitration, FlexRay designers must insure that their FlexRay systems are error-free.

Although low bit-error-ratios can be tolerated in todays computer systems, errors in safety-

critical automotive systems cant be tolerated for obvious reasons.

This paper will share some of the key learnings that Agilent Technologies and DependableComputer Systems GmbH (DECOMSYS) discovered during the investigation of a new

FlexRay oscilloscope measurement system, and how difficult FlexRay measurement

challenges were overcome. This paper includes several FlexRay measurement examples

showing how proper FlexRay signal integrity and timing can be verified.


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May 2007Page 2

What is FlexRay?What is FlexRay?

FlexRay technology is currently in an early

adoption phase and is expected to gain rapid

adoption in the next five years.

FlexRay technology is currently in an early

adoption phase and is expected to gain rapid

adoption in the next five years.

FlexRay is the next generation higher-performance, time-triggered/deterministic serial bus used in higher-end automobiles for

safety-critical x-by-wire systems.

Time-triggered means that serial communications are based on a

global time schedule.

X-by-wire could mean brake-by-wire, steer-by-wire,navigation/collision avoidance-by-wire. Faults/errors canNOTbe

tolerated in these safety-critical automotive applications.

What is FlexRay?

FlexRay is the next generation higher-performance, time-triggering/deterministic serial bus

used in higher-end automobiles for safety-critical x-by-wire systems.

This new time-triggered/deterministic serial bus for automotive applications simply means

that digital packets of information are always transmitted within a particular time-slotaccording to a FlexRay system global timing schedule. This eliminates the possibility of

communication collisions and arbitration common with the current CAN bus technology, and

makes this new technology an attractive alternative for some of tomorrows safety-critical

automotive applications.

Many of these safety-critical applications are referred to as x-by-wire systems, such as

steer-by-wire, brake-by-wire, navigation/collision-avoidance-by-wire. These types of

automotive systems which you will see in future automobiles must be error-free. Although

todays computers can tolerate low bit-error-ratios, safety-critical automotive systems must

induce zero errors for obvious reasons. This is why this new deterministic serial bus

architecture has been selected for these types of applications.

In addition to safety and reliability issues, x-by-wire technology will enable automotive

manufacturers to eliminate bulky mechanical linkages throughout the automobile, such as

the steering column. Not only will this reduce weight and improve efficiency, but this opens

up a myriad of future possibilities for applying new state-of-the-art electronic systems in the

automobile such as navigation, entertainment, comfort controls.


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May 2007Page 3

Verify signal integri ty of di fferential FlexRay signals.

Measure jitter and signal amplitudes using eye-diagrams.

Verify timing o f the FlexRay schedule relative to signals.

Find and debug errors quickly.

Detect static frame drop-outs.

Time-correlate mixed-signals (ECU, sensors, FlexRay signals).

Filter/trigger acquis itions on cycle-multiplexed data fields.

Electrical testing at extreme environment conditions.

Facilitate remote/in-car testing.

FlexRay Scope Measurement NeedsFlexRay Scope Measurement Needs

FlexRay Scope Measurement Needs

Agilent Technologies and DECOMSYS GmbH jointly conducted market research during2006 to better understand oscilloscope measurement needs of FlexRay system andcomponent designers.

The number one reason to use an oscilloscope on FlexRay signals is to determine amplitude

and timing margins of FlexRay signals. This is typically referred to as signal integritymeasurements. But measuring signal integrity of FlexRay signals requires a myriad ofspecialized oscilloscope tools/applications. The following are the primary oscilloscopemeasurement requirements that FlexRay designers from various leading automotivecompanies shared with Agilent and DECOMSYS during this investigation:

Measure jitter and signal amplitude margins using eye-diagrams

Verify timing of the FlexRay schedule relative to transmitted signals

Time-correlated error analysis

Detection of static frame drop-outs

Mixed-signal time-correlation of various automotive system signals

Filtered/triggered acquisitions on cycle-multiplexed frames

Testing at extreme environmental conditions

In-car testing capability

This presentation will address each of these issues with some tips & tricks on how toperform some of these required FlexRay measurements.


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May 2007Page 4

Why are FlexRay Signal IntegrityWhy are FlexRay Signal Integrity

Measurements Important?Measurements Important?

Differential

FlexRay signal

with glitch

FlexRay Decode

Shows HCRC

Error

Why are FlexRay Signal Integr ity Measurements Impor tant?

Only an oscilloscope can show the quality of digital signals. Although FlexRay is a digital

bus, todays higher speed digital signals still have analog characteristics especially when

systems have signal integrity problems. This screen image shows a classic example of an

aggressor signal coupling into a differential FlexRay signal producing a header CRC error.

Although a FlexRay protocol analyzer could also capture and display the error condition, it

could not give you any indication of what might have caused it. The oscilloscope providesadditional insight into signal integrity issues.


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May 2007Page 5

Switching Power Supply Noise CausesSwitching Power Supply Noise Causes

Signal Integrity ProblemSignal Integrity Problem

60 kHz Switching

Power Supply

Noise

FlexRay Decode

Shows HCRC

Error

Switching Power Supply Noise Causes Signal Integrity Problem

The cause of this particular signal integrity problem was quickly discovered using an

oscilloscope. When the scopes time base was re-scaled to show multiple FlexRay frames,

we could see that signal interference was occurring at a fixed 60 kHz rate. This was exactly

the frequency of this nodes switching power supply.


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May 2007Page 6

Oscil loscope EyeOscil loscope Eye--Diagram MeasurementsDiagram Measurements

Vertically cl osing eye due to noise

and/or insufficient signal level

Horizontally cl osing eye due to

ji tter and/o r si gnal timing errors

Eye-diagrams display worst-case jitter,vertical noise, & signal anomalies

Repetitive eye-diagrams

measurements require a reference

clock signal for oscil loscope triggering

FlexRay signals dont supply an

explicit reference clock signal

Triggering on the FlexRay signal itself

eliminates most jitter components

Oscilloscope Eye-Diagram Measurements

To evaluate jitter and timing errors on serial data communication signals, engineers

frequently use an oscilloscope to view overlaid bit intervals in an eye diagram display. But

creating a repetitive eye diagram on an oscilloscopes display requires a reference trigger

signal such as a clock. However, in many of todays serial communication protocols such as

FlexRay, the reference clock is not explicit it is embedded in the serial data signal. So

how can FlexRay hardware designers create eye diagrams on their scopes without an

explicit clock signal for reference?

First we will discuss a common but flawed technique that is currently being used by

some FlexRay engineers. Then we will explore two new recommended measurement

techniques that more reliably show worst-case FlexRay jitter and signal amplitude variations.


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May 2007Page 7

FlexRay EyeFlexRay Eye--Diagram Measurement TechniquesDiagram Measurement Techniques

Repetit ive Cycle-to-Cycle Eye

Repetit ive BSS Eye

Real-time Eye

FlexRay Eye-Diagram Measurement Techniques

A technique that some FlexRay designers are using today involves triggering on either edge

of the differential FlexRay signal. We call this type of FlexRay eye measurement a repetitive

cycle-to-cycle eye. There are some fundamental problems with type of eye measurement

which we discuss in more depth.

A better technique (in the opinion of the author of this paper) to measure all jitter not just

cycle-to-cycle jitter is a repetitive eye measurement based/triggered on Byte Start

Sequence (BSS) events.

Lastly, a rather new eye measurement technique known as the real-time eye will be

discussed. This technique uses software to recover a clock and create a folded eye-

diagram from a single-shot acquisition using a scopes deep acquisition memory.


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May 2007Page 8

FlexRay Repetitive CycleFlexRay Repetitive Cycle--toto--Cycle EyeCycle Eye--DiagramDiagram

Trigger Point

Trigger Condition = Either edge, hold-off = FlexRay cycle time

FlexRay Repetitive Cycle-to-Cycle Eye-Diagram

In the absence of an explicit reference clock signal to use as an oscilloscope trigger source

to create a repetitive eye diagram display, you might be tempted to set up your scope to

trigger on both rising and falling edges of the FlexRay differential signal. In an attempt to

insure triggering on all edges successively, you also might set the scopes trigger hold-off

time to exactly the FlexRay schedule cycle time. For instance, with an ideal cycle time of 5

ms, if the scopes trigger hold-off time is set to exactly 5 ms, then under ideal conditions the

scope will trigger once every cycle while stepping through the serial data stream triggering

on each edge of the signal successively. But because of differences in the stability of each

FlexRay nodes timebase relative to the accuracy of the scopes timebase, it is unlikely you

will achieve this ideal triggering condition. In most instances, the scope will not step through

the signal triggering on every edge successively, but will randomly trigger on most edges.

However, this method of creating FlexRay eye diagrams has other inherent problems.


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May 2007Page 9

Limitations of the Repetitive CycleLimitations of the Repetitive Cycle--toto--Cycle Eye TestCycle Eye Test

Only shows cycle-to-cycle jitter.

Only shows single bit-width signals.

Idle signal will be captured with in eye.

Susceptible to triggering on noise.

FlexRay Mask does not p rovide a idle

dead zone.

Limi tations o f the Repetitive Cycle-to-Cycle Eye Test

The biggest problem with this eye-diagram measurement technique is that when we triggeron the differential FlexRay signal itself, most measured jitter is eliminated. The only jittercomponent remaining in the measurement is cycle-to-cycle jitter. In addition, only bits of asingle bit-width are testing using this method. So this eliminates the ability to test for inter-symbol interference (ISI), or serial pattern dependent timing errors.

Secondly, with the scopes trigger level set near the 50% threshold level of the differentialFlexRay signal, which is necessary to create a vertically balanced eye-diagram, the scopewill occasionally trigger on overshoot or ringing of the frame end sequence (FES) pulse. Thissets up a situation where the idle time between frames may be captured and displayedwithin the eye. If you are performing a pass/fail mask test on this eye, then the FlexRaymask must include a dead-zone around the base-line (idle level) of the signal. In addition,in the naturally harsh and noisy environment of automobiles, the scope may trigger onrandom noise or interference riding on the base-line signal between frames. If a trigger eventcaused by base-line occurs just before a signal edge, then a signal edge will appear in themiddle of eye, indicating a severe FlexRay timing problem that may not actually exist.

Lastly, FlexRay masks currently defined in the FlexRay physical layer specification dont

provide a dead-zone in order to ignore the idle/base-line signal running through the middleof the eye. It would be desirable for a scope to automatically detect eye failures, but withoutthe complex dead-zone mask, scopes will indicate failures when the idle signal is captured.In addition, the FlexRay physical specification also position the left-most point of the maskexactly at the trigger reference point. Scopes with automatic mask failure detection willimmediately indicate a failing condition using this mask position.


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May 2007Page 10

FlexRay Timing DiagramFlexRay Timing Diagram

BSSTSS Byte 0 Byte 1 Byte NBSS BSS FES

FSS

Pulse width =100 ns to 900 ns

Hold-off = 950 nsConsistent

Trigger Event

Potential

Trigger Event

Potential

Trigger Event

1st BSS = 200 ns wide

2nd through Nth BSS = 100ns to 900 wide

950 ns tri gger hold-off = trigger on falling edge of BSS

Potential Trigger Event = Trigger if re-armed

Depends on acquisition/waveform update rate

FlexRay Timing Diagram

Rather than triggering on any edge of the FlexRay signal as described above, a better wayto create a valid FlexRay eye diagram is to set up the oscilloscope to trigger on a signalwithin each byte start sequence (BSS) event, which is the timing reference point for thetransmission of the following byte. But not all scopes have the required performance to makethis measurement. Triggering on a BSS pulse requires time-qualified pulse-width triggering

along with trigger hold-off. In addition, the scope must have a very fast waveform updaterate/re-arm time, and the scope should also have a pseudo-randomized start-of-acquisitionto insure triggering on most bytes.

As the timing diagram in screen image shows, for a 10 Mbps FlexRay baud rate, the width ofthe first positive pulse that contains the first BSS falling edge preceding byte number 0 is 200ns (2 bit periods). The positive pulse width of all successive pulses preceding BSS fallingedges can range from 100 ns to 900 ns. For example, if a particular byte contains all zeros,then the width of the pulse that contains the next BSS falling edge would be 100 ns (one bitperiod). But if the byte contains all ones, then the width of the pulse that contains the nextBSS falling edge would be 900 ns (eight bit periods plus the BSS pulse).

With a scopes pulse-width triggering set up to trigger on positive pulses wider than 50 ns

(which helps to avoid triggering on random noise/glitches) but narrower than 950 ns, thescope will trigger only on falling edges of the BSS pulse but only if the scopes triggerhold-off time is also set to 950 ns. This trigger hold-off setting will insure that the scope doesnot trigger on various-width data pulses within each byte. After the scope has synchronizedtriggering on the first BSS pulse of a frame, trigger hold-off will always arm the next triggerevent 50 ns before the next falling edge of the BSS event. Note that the next BSS eventshould always occur 1000 ns after the preceding BSS event.


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May 2007Page 11

BSS Pulses Captured by an OscilloscopeBSS Pulses Captured by an Oscilloscope

BSS BSS BSS BSS BSS BSS BSS BSS BSS

BSS Pulses Captured by an Oscilloscope

This oscilloscope display shows a similar timing diagram of a repetitive waveform capture of

the first nine bytes of a FlexRay frame using an oscilloscope. Note that with the scopes

timebase set to 1 s/div, we can see that the BSS events occur once every 1 s (1 division

apart).


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May 2007Page 12

Triggering on BSS Events toTriggering on BSS Events to

Show Successive 8Show Successive 8--bit Eyebit Eye--DiagramDiagram

BSS

Trigger Event

Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0BSS

&

FES

Trigger Conditi on = + Width: 50 ns to 950 ns, Hold-off = 950 ns

Triggering on BSS Events to Show Successive 8-bit Eye-Diagram

This oscilloscope display shows an example of triggering on BSS events using pulse-width

triggering and trigger hold-off. Although this may appear to be a non-standard eye-diagram

since it consists of eight waveform eyes, this is a perfectly valid technique to view the eight

individual bit fields.

Displaying a more conventional repetitive eye-diagram consisting of a single eye with all

eight bit fields overlaid on top of one another requires a few additional steps.


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May 2007Page 13

Repetitive BSS EyeRepetitive BSS Eye--Diagram of Bit #7 (MSB)Diagram of Bit #7 (MSB)

Bit #7


Timebase = 20 ns/div, Delay = 140 ns

Repetitive BSS Eye-Diagram of B it #7 (MSB)

Using the same oscilloscope triggering condition (+PW > 50 ns but < 950 ns, with hold-off =

950 ns), scale the scopes timebase to show just the first bit field (MSB), as shown in this

oscilloscope display. In this example, we have set up the time base scaling to 20 ns/div (5

divisions = 1 bit width) and the acquisition delay to 140 ns relative to center-screen. Note

that the first BSS trigger event is located 7 divisions (140 ns = 20 ns/div X 7 divisions) left of

center-screen.

Next, turn on the scopes infinite-persistence display mode to collect tens of thousands of

acquisitions of bit #7, which only requires a few seconds if the scope has a fast waveform

update rate.


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May 2007Page 14

Repetitive BSS EyeRepetitive BSS Eye--Diagram of Bit #6 and Bit #7Diagram of Bit #6 and Bit #7

Bits #6 & #7


Timebase = 20 ns/div, Delay = 140 ns, 240 ns

Repetitive BSS Eye-Diagram of Bi t #6 and Bit #7

After collecting a sufficient number of acquisitions of bit #7, turn off the infinite-persistence

display mode, but dont clear the infinite-persistence display of bit #7. Then change the

scopes acquisition delay time by an additional 100 ns (one bit width) to 240 ns. Next, turn on

the infinite-persistence display mode once again to collect thousands of overlaid acquisitions

of bit #6 overlaid on top of the previously captured bit # 7 waveforms, as shown in this

scope display.


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May 2007Page 15

Repetitive BSS EyeRepetitive BSS Eye--Diagram of ALL Bit Fields (#0Diagram of ALL Bit Fields (#0

through #7)through #7)

Bits # 0-7

Trigger Conditi on = + Width: 50 ns to 950ns, Hold-off = 950 ns

Timebase = 20 ns/div, Delay = 140 ns, 240 ns... 840 ns

Repetitive BSS Eye-Diagram of ALL Bit Fields (#0 through #7)

Repeat the above process with acquisition delay settings of 340 ns through 840 ns to create

a repetitive eye-diagram of all eight bit fields based on the reference BSS events, as shown

in this scope display.

For this multi-step measurement to create an overlaid eye-diagram of all eight bit fields, youneed a scope with a very fast waveform update rate and dithered repetitive acquisitions

using equivalent-time sampling in addition to precise pulse-width triggering and trigger

hold-off.

Fast waveform update rates are important for two reasons. First, you need to collect

thousands of acquisitions of all bit fields to insure statistical validity of the eye-diagram

measurement. Secondly, fast waveform update rates are required to insure that the scope

triggers on multiple bytes within each frame. If the scope updates acquisitions slowly, the

scope will always synchronize its acquisition on just the first BSS of each frame.

A dithered start-of-acquisitions is required to prevent the scope from triggering on every

Nth BSS trigger event, thereby skipping multiple bytes. Agilent scopes employ dithered start-

of-acquisitions when you are using the equivalent-time sampling mode. This dithered

technique of acquisitions was employed in Agilent scopes primarily to prevent the possibility

of synchronizing repetitive acquisitions with the signal under test. If this happens, you may

see holes in the displayed waveform. But this dithered start-of-acquisitions technique also

insures that random bytes of the FlexRay frame are triggered on, thereby improving the

statistical validity of the repetitive eye-diagram measurement.


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May 2007Page 16

Limitations of the Repetitive BSS Eye TestLimitations of the Repetitive BSS Eye Test

Currently a manual multi-step test.

Not all scopes allow PW triggering AND

trigger hold-off simultaneously.

Not all scopes allow set up changes

while using infinite-persistence.

Scope re-arm t ime (1/dead-time)

eliminates acquisition of some bytes.

Not all scopes dither start-of-

acquisitions.

Currently defined FlexRay masks only

defined for cycle-to-cycle jitter

component.

Limi tations of the Repetitive BSS Eye Test

Although the repetitive BSS eye-diagram measurement method is superior for measuringworst-case jitter and signal amplitude deviations relative to the cycle-to-cycle eye-diagrammeasurement (in the opinion of the author of this paper), this method of creating a repetitiveeye-diagram is not without its limitations.

As you just seen in this presentation, creating a single eye is a multi-step process foroverlaying individual bit fields one at a time. In addition, not all scopes on the market todayhave the required triggering and display features required for this testing method. Forinstance, some scope dont permit setting a specific trigger hold-off time while using pulsewidth triggering. And most scopes on the market dont allow the user to change setupconditions, such as delay time, while using the infinite-persistence display mode. As soon asa set up is changed, the infinite-persistence display is erased and starts over.

Although it would be desirable to capture all bytes of a FlexRay transmission, oscilloscopere-arm/waveform update rates limits which bytes are captured. Once the scope triggers onthe first BSS event in a particular frame, it is impossible for the scope to re-arm itself in timeto capture the second BSS event. This would require a waveform update rate in access of1,000,000 waveforms per second. Closely related to this issue is dithering of start-of-

acquisition process, which is not available in all scopes. Without dithering, the scope will onlycapture every Nth BSS event based on its re-arm time or waveform update rate.

Finally, FlexRay mask standards defined in the FlexRay physical layer specification onlyapply to cycle-to-cycle eyes. Repetitive or real-time eye-diagrams created using the BSSevent as the reference timing event will typically show more jitter than whats allowed for inthe currently defined FlexRay masks.


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May 2007Page 17

FlexRay RealFlexRay Real--Time EyeTime Eye--DiagramDiagram

BSS BSS

1 1 1 1 1

000

FlexRay Signal

Folded Real-time Eye

FlexRay Real-Time Eye-Diagram

Another measurement technique to create FlexRay eye-diagrams is the real-time eye.Although automotive embedded designers may be unfamiliar with this type of measurement,this is a very common measurement used on high-speed serial buses, such as PCI-Express(2.5 Gbps). Creating a real-time eye requires a deep-memory, real-time oscilloscope with areal-time eye measurement option that recovers the buss embedded clock using a software

clock recovery algorithm. For some high-speed serial bus standards, the scopes softwareclock recovery algorithm can be quite complex, such as recovering clocks from systemsbased on spread spectrum clocking and a phase lock loop (PLL) clock recovery hardware.But for the FlexRay protocol, the software clock recovery algorithm is very simple. Thescopes software assumes a fixed 10-MHz clock synchronized to each BSS event.

For a FlexRay real-time eye, the scope should first capture multiple FlexRay frames usingdeep acquisition memory. The triggering technique is not critical typically a simple edgetrigger condition is all you need. The scope then searches through its deep memory recordto locate each BSS event. The first BSS event of each frame is the first complete fallingedge. Each successive reference BSS event will be a falling edge that occurs approximately1 s later. The scopes software precisely locates each of the events. The algorithm thenslices the bit fields of each byte into perfect 100 ns mini-records. These 100 ns mini-records are then overlaid on top of one another to recreate the real-time (or folded) eye from

a single acquisition.

Although real-time eyes are typically created using a single deep-memory acquisition thatcan capture multiple FlexRay cycles, this type of measurement can also be set up to runrepetitively to overlay multiple real-time eyes to look for long-term anomalies. If and when amask violation occurs, the last eye can be unfolded in to analyze the specific bit failure.


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May 2007Page 18

FlexRay Real-Time Eye

FlexRay Real-Time Eye

As you can see in the scope display, a real-time eye looks exactly the same as a repetitive

eye. However, real-time eyes can be created in software using a single acquisition. You can

only find real-time eye measurement capabilities in todays higher-performance, Windows-

based scopes. In addition to performing real-time eye measurements, these scopes also can

automatically perform jitter analysis, including separation of various random and

deterministic components of timing error. Although real-time eyes and jitter analysis based

on the FlexRay protocol are not currently available from any oscilloscope vendor, this

measurement capability may become available in the near future.


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May 2007Page 19

Limitations of the RealLimitations of the Real--time BSS Eye Testtime BSS Eye Test

Currently not available from any vendor.

Currently defined FlexRay masks only

defined for cycle-to-cycle jitter

component.

Will require a Windows-based, non-

battery operated scope.

Limi tations of the Real-time BSS Eye Test

Although the real-time BSS eye-diagram measurement method is probably the most reliable FlexRay

eye-diagram measurement technique, this method of measuring a FlexRay eye is not currently

available from any oscilloscope vendor. However, once this measurement capability becomes

available, FlexRay engineers will be able to create eye-diagrams based on all bits, all bytes, and all

frames of a complete FlexRay cycle, from a single acquisition using a deep memory oscilloscope. In

addition, a Windows-based scope will be able to perform statistical jitter measurements at the crossingedges using histogram measurements.

Another limitation of this measurement technique is the lack of defined FlexRay masks based a Byte

Start Sequence (BSS) eye.


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May 2007Page 20

Why is the FlexRay Timing Trace Important?Why is the FlexRay Timing Trace Important?

Verify timing of slot and segment boundaries

Why is the FlexRay timing trace important?

Part of the deterministic nature of the FlexRay protocol is that it is based on a time-triggered

architecture. This means that FlexRay signal transmissions must occur within a specified

window of time. Verifying timing of physical layer FlexRay signals to the systems specified

timing schedule (usually specified within a FIBEX file) is very important to FlexRay designers

in order to eliminate possible timing errors in their designs.


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May 2007Page 21

Why is hardwareWhy is hardware--based decoding impor tant?based decoding important?

1. Fast waveform/decode

update rates enhance

usability2. Enhances probability of

capturing and decoding

infrequent errors

Infrequent Header CRC Error

Why is hardware-based decoding important?

Waveform and FlexRay decode update rates are important for two reasons. First of all, fast

waveform/decode update rates provides for responsive measurements making the

oscilloscope easier to use. Secondly, and probably most important, real-time decode update

rates enhance the probability of the scope to capture random and infrequent error conditions.

Most oscilloscopes on the market today utilize software decoding techniques. This means

that waveform and decode update rates can take seconds especially when using deep

memory to capture multiple packets of FlexRay transmissions. If random errors occur, they

will probably occur during the scopes data-processing dead-time.

Hardware-based FlexRay decoding provides real-time responsiveness and enhanced error

detection.


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May 2007Page 22

Why is robust FlexRay error analysis required?Why is robust FlexRay error analysis required?

Eliminating errors in safety-critical

automotive systems is CRITICAL!

Header CRC Error Message

Why is robust FlexRay error analysis required?

For safety-critical FlexRay systems, it is extremely important to eliminate all possible errors.

After all, when we turn the steering wheel to avoid a collision, dont we want the electronic

steering system to respond immediately? Identifying errors goes beyond just detecting CRC

errors. What about possible timing errors such as slot boundary violations? A robust set of

error messaging and oscilloscope triggering enables FlexRay designers to debug their

systems before they reach the customer.


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May 2007Page 23

Why is Static Slot DropWhy is Static Slot Drop--out Detection Important?out Detection Important?

Static Frame Drop-out

Why is Static Slot Drop-out Detection Important?

Although transmitting frames during the dynamic segment is optional, if an ECU/node is

assigned a particular static slot to communicate in, it must transmit a frame of a fixed length,

even if it has nothing to say. If it has nothing to say, then a null frame should be transmitted.

In this example, we show a static frame (ID:39) that occasionally drops-out, which is aviolation of the FlexRay protocol.


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May 2007Page 24

Triggering on Empty (but assigned) Static SlotsTriggering on Empty (but assigned) Static Slots

Empty Slot

Triggering on Empty (but assigned) Static Slots

By setting up to the scope to trigger on Slot-Type: Empty, the scope will only trigger and

capture waveforms if specified slot (#39) is empty. This type of FlexRay oscilloscope

triggering can be especially useful when looking for very infrequent drop-out conditions, in

which case the scope could be setup to trigger on this condition for an overnight test.


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May 2007Page 25

Why are MixedWhy are Mixed--Signal Measurements Important?Signal Measurements Important?

Vehicle analogsensor inputs

Differential

FlexRay signal

ECU digital

control signals

FlexRay timing &frame decode

traces

Time-correlate:

+

+

+

Why are mixed-signal measurements important?

Automotive electronic systems are by definition mixed-signal systems consisting of multiple

analog, digital, and serial signals. As stated earlier, FlexRay designers indicated that they

needed the ability to correlate multiple mixed-signal activity within their automotive systems.

A mixed signal oscilloscope (MSO) is a natural fit for these types of measurements. With an

MSO, designers can easily view and time-correlate their analog sensor inputs, their

differential serial signals, such as FlexRay, and their digital control and I/O signals within

their ECUs using a single instrument. And with advanced FlexRay triggering and decoding,

they can also correlate all of the mixed-signals to the FlexRay bus.


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May 2007Page 26

Why is FlexRay CycleWhy is FlexRay Cycle--Filter Triggering Important?Filter Triggering Important?

Unfiltered (All) Cycle Triggering

Cycle-multiplexed data

Why is FlexRay Cycle-Filter Triggering Important?

Because of the multiplexed communication possibilities that the FlexRay protocol allows,

FlexRay designers want to be able to trigger oscilloscope acquisitions on particular

communication cycles not just cycle number, but triggering based on cycle-repetitive rate

and cycle- base number.

This scope display shows an example of capturing repetitive acquisitions while triggering a

particular FlexRay frame (ID: 38). This frame includes a multiplexed data field, which we can

observe when triggering on all cycles. Perhaps this frame transmits various engine

diagnostic parameters. Capturing just cycles that apply to specific parameters, such as oil

pressure or temperature requires cycle-filter triggering.


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May 2007Page 27

FlexRay CycleFlexRay Cycle--Filter Triggering: BaseFilter Triggering: Base--RepRep

Cycle/trigger filtering: Repetition = 4, Base = 0

Engine diagnostics parameter #1

FlexRay Cycle-Filter Trigger: Base-Rep

With cycle base-rep triggering, the scope can filter its triggering on a repeating pattern of

cycles. In this example we show that with a cycle repetitive of 4 and base of 0, the scope

only captures cycles 0, 4, 8, 12, 16... (0, 0+4, 0+4+4, etc.). Perhaps the engine diagnostic

ECU (frame ID:38) transmit engine temperature during these particular cycles.


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May 2007Page 28

FlexRay CycleFlexRay Cycle--Filter Triggering: BaseFilter Triggering: Base--RepRep

Cycle/trigger filtering: Repetition = 4, Base = 1

Engine diagnostics parameter #2

FlexRay Cycle-Filter Trigger: Base-Rep

If we change the cycle-base number to 1, the scope now triggers on and captures just

cycles 1, 5, 9, 13, 17... (1, 1+4, 1+4+4, etc.). Perhaps the engine diagnostic ECU (frame

ID:38) transmit engine oil pressure during these particular cycles.


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Remote inRemote in--car testing requires battery operationcar testing requires battery operation

Remote in-car testing requires battery operation

Although FlexRay systems should be thoroughly tested on the bench and under simulated

environmental conditions, they should also be tested under real-world conditions. This

requires in-car testing under various extreme driving conditions. Evaluating signal fidelity

with an un-tethered oscilloscope requires a scope that performs FlexRay measurements

under battery operation.


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Testing Automotive Systems in ExtremeTesting Automotive Systems in Extreme

Environment ConditionsEnvironment Conditions

Precision Gore extension cables compatible with Agilents InfiniiMax active probes allowdifferential active probing within environmental chambers at extreme temperatures.

Testing in extreme environmental condi tions

Signal integrity measurements on automotive differential signals such as the physical layer

of the FlexRay serial bus requires differential active probing. In addition, FlexRay designers

must often test their embedded designs under very extreme conditions in environmental

chambers. These extreme conditions may include testing ECUs and differential serial buses

at temperatures exceeding 100 degrees Celsius. Unfortunately, the active circuitry in todays

typical active probes cannot tolerate temperatures exceeding 55 degrees C. However, with

the unique electrical and physical architecture of the 1130 Series InfiniiMax active probes,

SMP microwave extension cables from Gore (Gore part number PRP042105-01) can be

used to extend and displace the probes active amplifier to be outside of an environmental

chamber. With this configuration, InfiniiMax passive probe heads can be connected to test

points within the chamber with temperatures exceeding 100 degrees C.


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FlexRay Presents New Challenges forFlexRay Presents New Challenges for

Oscilloscope MeasurementsOscilloscope Measurements

Summary FlexRay signal integrity measurements

require an oscilloscope.

FlexRay eye measurements should be

referenced to Byte Start Sequence

events.

Debugging FlexRay systems requires

sophist icated FlexRay real-time pro tocol

triggering and decoding.

Summary

The fundamental tool to perform signal integrity measurements is an oscilloscope. A test

often used to check for valid signal fidelity is the eye diagram. Creating a repetitive eye-

diagram requires establishing scope triggering on Byte Start Sequence events. Alternatively,

a real-time eye can be created using a custom clock recovery algorithm that slices a deep

memory acquisition into bit intervals and then overlays the bits.

Debugging FlexRay systems can be greatly enhanced using an oscilloscope with FlexRay

triggering and decoding, including error analysis.


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