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AR# 29983

XST - Why does XST generate too many DSPs and BRAM, resulting in an overmapping error?

Description

XST generates more DSPs and BRAM available (even though the DSP/BRAM utilization ratio is set to 100). This results in an overmapping error.

Why does XST utilize more DSP or BRAM than is available?

Solution

This problem can occur for one of two reasons:

- If XST property "Read Cores" is turned off and the core has a lot of BRAM or DSP block instantiated. XST has no way of accounting for the block instantiations in the core if the "Read Cores" is turned off.

- The problem related to XST's automatic resource management as the BRAM and certain types of DSP are not calculated in the total number available, resulting in over inference.

To work around the issue of too many DSP being inferred, reduce the DSP utilization ratio to < 100.

This option can be found in the XST options within Project Navigator, or it can be changed from the command line by setting the "-dsp_utilization_ratio <integer>" switch.

To work around the issue of too many BRAM being inferred, reduce the BRAM utilization ratio to < 100.

This option can be found in the XST options within Project Navigator, or it can be changed from the command line by setting the "-bram_utilization_ratio <integer>" switch.

If this does not help you resolve the problem, open a WebCase with Xilinx Technical Support at: http://www.xilinx.com/support/clearexpress/websupport.htm

AR# 29983
Date Created 03/07/2008
Last Updated 01/27/2013
Status Active
Type General Article