When Is the Best Time to Use Xsignal?

The Create xSignals Between Components Wizard can be run multiple times – choose a different sub-set of input pins, define classes and rules for them, then run the Wizard again. The new xSignals will appear on the xSignal Routes panel and in the PCB layout.

The xSignal Mode panel displays the xSignals in a list, with each xSignal displayed as a thin line in the design space. The middle region presents xSignal class management buttons.

1. Design Rule Support

Static analysis tools are often pre-configured to check for specific universal design rules that reflect constraints on the architecture (e.g., PMD [41] and FindBugs [69]). Extensible static analysis tools enable developers to author their own custom rules that capture project-specific decisions in a checkable format. These may be documented as AST patterns using special notations or expressed as program analysis code in general purpose programming languages.

The xSignal panel’s xSignal Classes region lists any xSignal class collections that have been defined and provides a management button to allow you to export or import a list of rule types. The Edit xSignal Class dialog allows you to set the parameters that will define the class. Managing the xSignal Class allows you to scope the Matched Length and Other Rules design rules and their requirements during tasks such as interactive length tuning.

2. Interactive Length Tuning

Creating high speed signal routing in a PCB is a time-consuming task that requires careful length tuning of all tracks and arcs. In previous Altium versions, this was done by running the Length Tuning command in the PCB Rules and Violations panel for either a single net or a differential pair of nets (depending on the mode selected).

This panel also allows you to see which xsignal products are tuned. Those that are not tuned will be highlighted in a darker color. Those that have been tuned will be highlighted in a lighter color.

A xSignal is a union of primitive track and arc segments with full control over the amplitude, gap, and corner radius (or miter). Like other group objects in the design, such as components, dimensions, and polygons, a xSignal can be exploded to reveal its constituent-free primitives, and then modified independently.

3. T-Branch & Fly-By

The T-topology routing for command, address and clock signals is ineffective at higher signal speeds. It’s replaced on DDR3 and later versions with a “Fly-by” topology which routes the command, address and clock signals in a chain from the controller to each memory device while still connecting the data lines directly. This reduces the number of stubs and increases signal integrity.

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4. Routing Rules

The Routing Rules section enables you to define the way messages are routed. Each rule has a type and a description. Types are either BLOCK or ALLOW. BLOCK means that the message will be blocked if any of its matchers is not matched while ALLOW means that the message can be relayed if all of the rule’s conditions are met.

Alternatively you can choose Process-only which does all of the same things as Route except that it doesn’t send any outbound message. This can be useful if you want to set values to a conversation for later use, like when creating a report.

There is also a dropdown to choose which action the rule should take after matching. This allows you to configure if the message should be processed, dropped or routed. The priority option allows you to specify the order in which rules are handled. This is a very useful feature to help with routing complex conversations.