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AR# 14518

5.1i CORE Generator - Asynchronous FIFO outputs RD_COUNT and WR_COUNT do not increment/decrement properly in simulation


General Description:

When I run the simulation (behavioral and timing) process, the RD_COUNT and WR_COUNT outputs do not increment or decrement properly. This behavior occurs in simulation (behavioral and timing) as well as in the device.


This failure is more apparent when the RD_CLK and WR_CLK are running asynchronously and when read and write operations are being performed simultaneously.

This issue occurs because of the asynchronous nature of the core. This is not a bug in the Asynchronous FIFO core, but is rather a limitation of asynchronous cores.

The WR_COUNT and RD_COUNT values should NOT be used to obtain the accurate data count of the Asynchronous FIFO, as the value may be off by a few counts at any given time. The WR_COUNT and RD_COUNT should be used as a gauge to determine the FIFO status. Although the outputs of the RD_COUNT and WR_COUNT values appear to be incorrect, the basic functionality of the Asynchronous FIFO is not affected, and it will continue to read and write properly.

AR# 14518
Date Created 08/29/2007
Last Updated 12/15/2012
Status Active
Type General Article