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AR# 7555

XPLA Professional: Simulator runs for long periods of time.

Description

Keywords: XPLA, Professional, CoolRunner, fitter, simulator

Urgency: Standard

General Description: Why does the simulator occasionally run for long
periods of time?

Solution

The main reason for very long simulation times are often due to
unknown or undefined states of internal nodes during the simulation.
You must be careful using busses. The tri-state level of the bus can
easily introduce undefined states into the network. This is the same
problem you can get with the hardware. If you have tri-state inputs to
logic, the outputs can start oscillating. The output will be undefined
and the simulator will continuously calculate the new internal levels
of the network. This results in very long simulation times and very
large *.res files because every new state is written into the *.res file.

Under normal conditions, the simulator calculates until there is a
stable network condition. After this it is just waiting for the next stimuli
after a SU command in the *.scl file. The way to find out which signal
is unstable, you can use the command LIST# to detect which signals
are unstable at a certain position in the simulation. This can be after
a BUSI or BUSO command in this file.

This condition may also be caused by video board color settings which
is discussed at (Xilinx Solution 7507).
AR# 7555
Date Created 09/14/1999
Last Updated 08/31/2001
Status Archive
Type General Article