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AR# 21083

7.1i Spartan-3 PAR - Incomplete message about turning off Local Clock placement


Keywords: MAP, -timing, placer

When I run MAP with the -timing option, my design fails with the following messages regarding placement failures:

"ERROR:Place:543 - Due to placement constraints, the following 1 components
cannot be placed. The relative offsets of the components are shown in
brackets next to the component names.
FF imac/mr_top/mac_readblock/mac_rdwt2/BBD_dat_1[1] (0, 0)"

(Previous message repeated for other components)

"ERROR:Place:544 - The placement constraints may have been generated by the Local Clock placer. To allow map -timing to complete, please try running map
-timing with Local Clock placement turned OFF."

There is also a message stating that the placement failures might be due to something called "Local Clock Placer" and that I should disable it. What does this mean?


The "Local Clock Placer" is a placement algorithm that attempts to place the loads of a local clock (clock net driven by standard I/O, rather than global buffer) in such a way that they can be routed with low skew. This algorithm creates some internal area constraints that, when combined with user constraints, can make the design difficult to place successfully and results in the errors mentioned.

The Local Clock Placer can be disabled by setting the following environment variable:


Linux and Solaris:

NOTE: Prior to 7.1i SP3, the variable name was PAR_NOIORGLLOCCLKSPL. Both will work in SP3 and later versions.

When you encounter these errors, it can be useful to set the environment variable work-around to confirm that the local clock placer is involved with the placement problems. If this eliminates the errors, then the local clock routing results should be examined to determine whether the results are acceptable. If it does not eliminate the errors, the following steps might help resolve the problem:

1. Move large local clocks to global buffers.
2. Floorplan or otherwise constrain the local clock loads.
3. Relax user constraints so that the automatic placer has more freedom.

For more general information about setting ISE environment variables, see (Xilinx Answer 11630).
AR# 21083
Date 10/19/2008
Status Archive
Type General Article