Knowledge Base Article
Why can't I observe any activity on the Triple Speed Ethernet MegaCore Functions RGMII_OUT signals in the SignalTap II Logic Analyzer?
Description
The RGMII_OUT registers are implemented using Alt DDIO_OUT atoms which cannot be observed using SignalTap™ as a routing path to the core is not possible. Hence it is not possible to signaltap these nodes.
In the SignalTap II Logic Analyzer, the RGMII_OUT signals are only visible by selecting “SignalTap II: pre-synthesis” as filter, however after compilation, from the Compilation Report > Analysis & Synthesis > In-System Debugging, you will find that the status of the RGMII_OUT signals are illegal and these signals are connected to GND.
If you change SignalTap II’s filter to “SignalTap II: post-fit”, you are unable to find the RGMII_OUT signals.
Resolution
The functionality of the RGMII_OUT (DDIO_OUT) block is unaffected and you are able to scope the output signal on your board.