Teledyne LeCroy FlexRay Trigger, Decode and Physical Layer Test - Manual (Page 8)

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FlexRay-TDP-OM-E Rev A
TECHNICAL OVERVIEW OF D, TD, AND TDP OPTIONS
LeCroy’s offering of FlexRay trigger, decode and physical layer test options utilize advanced trigger circuitry and
advanced software algorithms to provide powerful capability for serial data triggering and decoding.
FlexRay Trigger
FlexRay TDP and TD options contain advanced serial data triggering. This serial data triggering is implemented
directly within the hardware of the oscilloscope acquisition system, and contains advanced algorithms to protocol
decode, recognize, and trigger on user-defined serial data patterns. This allows a recognized serial data pattern
to be used to trigger the oscilloscope at a pre-determined time, and other signals coincident with the desired serial
data pattern can be captured simultaneously.
FlexRay Decode
FlexRay TDP, TD and D options contain powerful protocol decoding and annotation software algorithms. The
software algorithm examines the embedded clock for each message based on a default (or user set) vertical
levels. The algorithm is intelligent in that it applies a hysteresis to the rising and falling edge of the serial data
signal to minimize the chance that perturbations or ringing on the edge affect the decoding. The default levels are
set to 30% and 70% and are determined from a measurement of peak amplitude of the signals acquired by the
oscilloscope. It can also be set to (absolute) voltage levels, if desired. The algorithm then performs an analysis of
the serial data message to determine the nominal bit width.
After determining bit width, a different algorithm performs a decoding of the serial data message into binary format
after separation of the underlying data into logical groups (TSS, FSS, Frame Qualifiers, ID, Payload Length, CRC,
Payload Length Code, Data, BSS, Data Length Codes, Data, FES, etc.). Finally, another algorithm provides the
appropriate color coding of the message, and displays the protocol message data on the screen, as desired,
overlaid on the source trace. Various compaction schemes are utilized to show the data during a long acquisition
(many hundreds or thousands of serial data messages) or a short acquisition (one FlexRay frame acquisition). In
the case of the longest acquisition, only the most important information is highlighted. In the case of the shortest
acquisition, all information is displayed with additional highlighting of the complete message frame.
Note: Although the decoding algorithm is based on a clock extraction software algorithm using vertical levels, the results returned are the
same as those from a traditional protocol analyzer using sampling point-based decode. In addition, the clock extraction technique allows
partial decoding of messages in the event of physical layer noise, in many cases, whereas a protocol analyzer usually cannot. This is a
significant advantage for the LeCroy software algorithm.
If the sampling rate (SR) is insufficient to resolve the signal adequately based on the bit rate (BR) setup, then the
protocol decoding is turned OFF to protect the operator from incorrect data. The minimum SR:BR ratio required is
4:1. It is suggested to use a slightly higher SR:BR ratio if possible, and significantly higher SR:BR ratios if you
also want to view perturbations or other anomalies on your serial data analog signal.
FlexRay Physical Layer
FlexRay TDP contains a software algorithm which creates eye diagrams, performs mask testing and measures
timing parameters as defined in the FlexRay specification. The algorithm creates eye diagrams by slicing up all
the bits transmitted in the FlexRay signal and superimposing each bit on to an eye diagram. The signal is sliced
based on measurements taken at the falling edge of the first Bytes Start Sequence (BSS) and the time between
consecutive BSS symbols. These measurements allow the algorithm to compute the rate of the embedded clock
and slice the FlexRay waveform in to sub-waveforms that are one bit in length. The clock uses a constant bitrate
specified by the user and is resynchronized on every BSS. These sub-waveforms are then scaled to fill 8
horizontal divisions on the oscilloscope and represent 1 Unit Interval (UI) in the eye diagram and superimposed
on top of each other.
Mask testing can be performed on the eye diagram with masks defined at TP1 and TP4. The mask is aligned
horizontally by computing the time for a single UI and centering it on the display. The mask is centered vertically
around 0V.
Along with eye diagrams and mask testing the TDP option adds 4 FlexRay specific measurements to the
oscilloscope. These measurements are Propagation Delay, Asymmetric Delay, Truncation, and Jitter. They
are measured as defined in the FlexRay specification. These measurements characterize timing properties of the
propagation of signals along the communication channel.