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AR# 21531

7.1i Virtex-4 PAR - Placer has difficulty finding legal placement of block RAM driven by two BUFRs

Description

Keywords: BRAM, BLKRAM, unrouted

Urgency: Standard

General Description:
A case has been seen where a block RAM with two clocks driven by BUFRs was placed in an unroutable configuration.

BUFR clock buffers have the restriction that they can only reach clock loads in the same or vertically adjacent clock region. The placer is currently unable to handle the situation of a single component driven by two BUFR clocks where the location of both BUFRs must be accounted for. This situation is most likely to be encountered with block RAM components.

Solution

To work around this issue, lock the location of all components driven by the two BUFRs along with the BUFRs. A change is planned for version 8.1i where the placer will print an error message regarding this limitation.
AR# 21531
Date Created 09/04/2007
Last Updated 10/23/2008
Status Archive
Type General Article