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AR# 16044

5.1isp2 XPower - "WARNING:Power:525 - Register output signal "cnt<1>" has not had its activity set" (The VCD file does not set the frequency of register outputs.)


Keywords: output, VCD, counter, XPower, frequency, activity

Urgency: Standard

General Description:
After I load a VCD file into XPower, the frequency of the register outputs is not being set. The following warning is reported:

"WARNING:Power:525 - Register output signal "cnt<1>" has not had its activity set."

What problem does this warning indicate?


This issue is fixed in the 5.2i release.

A bug in the tools prevents the outputs of registers from being set in certain situations. To work around this issue, you must manually set the frequency.

The register outputs are not set when a signal from a register is used as feedback to the same register. The signal must pass through the LUT as a route-through, and it must be the only input signal to the LUT. (This is typically seen in counters.)

NOTE: The bug is not the only cause of this warning; this message is also reported if the signal in question does not toggle in the VCD file.

You can use one of the following methods to verify whether or not the signal frequency should be set automatically by the VCD file:

Method 1
1. Open the VCD file and search for the signal name. In the above case, the following line indicates that the signal is being monitored in the VCD file:
$var wire 1 O! cnt [1] $end
2. Search for the identifier "O!" in the file:

The above information indicates a transition, which should be picked up by XPower.

Method 2
The second way to determine whether the frequency should be set is to look at ModelSim. To do this, you must know exactly what signals you are adding to the VCD file, and then inspect them in the wave window to ensure that they are being toggled.

For example, if you type the VCD add command as follows, this will typically only add the testbench signals:

vcd add /*

The correct syntax is as follows:

vcd add testbench/uut/*
AR# 16044
Date Created 10/31/2002
Last Updated 11/03/2004
Status Archive
Type General Article