Agilent Measurement Journal - Issue 5 - 2008 - (Page 60)

Rather than the approaches outlined above, what’s required is a measurement tool that combines a number of key capabilities. The tool must, for example, use thresholds from the FlexRay speciﬁcation to detect all bit transitions and have the ability to synchronize constantly on the byte-start sequence (BSS) of the FlexRay signal. This latter capability will help avoid problems associated with different clocks. The optimal tool should also be able to detect all bit transitions without any dead time. Additionally, the tool must use the appropriate multiple of the bit time — including the tolerance — to check for correctness at consecutive sequences of ones and zeros. As previously mentioned, such a measurement tool is currently not yet available. However, corresponding developments and tests are currently underway that should enable the industry to soon create this type of measurement device. The description of the quality requirements for the protocol layer of a speciﬁc FlexRay network must be created by the network developer or in accordance with the speciﬁcations and requirements document. Because the typical controller used for FlexRay networks suppresses or ﬁlters out most error situations, developers need different measurement tools to identify these errors. The common tool of choice for such measurements is the protocol analyzer. For this task, the ideal protocol analyzer must be capable of decoding and displaying the signals within a FlexRay network. Powerful triggering capabilities are also critical because these enable the developer to check for protocol errors and relevant events. To extract the necessary signal decoding, the protocol analyzer must support the latest FlexRay speciﬁcation as well as common ﬁle formats such as Fibex ﬁles. The ideal protocol analyzer must also be capable of handling issues speciﬁc to FlexRay networks. For example, to support a higher update rate for speciﬁc signals, the FlexRay speciﬁcation allows multiplexing of signals in several static slots. This alleviates the need to reduce the entire cycle time just to fulﬁll the need of one signal. As a result, the protocol analyzer must be able to detect such a situation and correctly display dependent signal values which have been evaluated for consistency across multiple slot boundaries. Working at the protocol layer There is no commonly agreed-to solution for the FlexRay protocol layer. This is due primarily to the layer’s complexity. Deﬁning a clear quality measure depends heavily on the application as well as the nature of the transmitted signals. Further complicating matters, errors in the protocol layer are often very broad and diverse. In general, they relate to the following questions: • How often are signal updates expected? • What is the maximum change rate of this signal? • How well can missing packets (e.g., ZeroFrames) be tolerated? • How are timing violations (e.g., slot violations in the static segment) checked? • Is it possible to use, as an example, running counters as part of the payload to detect packet loss? If so, how are such errors detected and caught? Figure 3. An example of an eye diagram in which a random timing violation occurred. 60 Agilent Measurement Journal

Table of Contents Feed for the Digital Edition of Agilent Measurement Journal - Issue 5 - 2008

Agilent Measurement Journal Issue 5 Finding a New Path when Assumptions Break Down Contents Testing MIPI D-PHY Protocols Oscilloscope Firmware Update DNA Replication Joining the LTE/SAE Trial Initiative Testing Proteins Praise for DC Power Analyzer Scripting Features for AMDS Testing Hybrid PCBA Systems Improving the Gene Expression System Workflow Turning a “Good Enough” Test Strategy into One That’s Reliable, Repeatable and Traceable Understanding the Effects of Limited-Bandwidth Channels on Digital Data Signals Introducing the 3GPP LTE Downlink Validating the 26 Validating the Physical and Protocol Layers in DDR Memory Interfaces Understanding Total Jitter Measurements of Low Probabilities Using Behavioral-Model Simulation to Accurately Predict First-Order PLL Performance Creating Synchronous High-Frequency Sampling across Multiple Digitizers Overcoming the Challenges of Testing FlexRay Networks Understanding Operating Life and Repeatability of Electromechanical Switches and their Effect on Total Cost of Ownership Implementing Micro and Nano LC/MS Techniques for High Sensitivity Lipidomics Analysis

Agilent Measurement Journal - Issue 5 - 2008

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