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AR# 14898

6.1i CPLD TAEngine - The fitter renames and rewrites OFFSET timing constraints as FROM:TO constraints

Description

General Description: 

When I run a design that contains OFFSET constraints, the constraints are renamed and rewritten in the form of FROM:TO constraints.  

 

For example

 

Given the following UCF file: 

 

NET "clk" TNM_NET = "clk"; 

TIMESPEC "TS_clk" = PERIOD "clk" 10 ns HIGH 50 %; 

OFFSET = IN 10 ns BEFORE "clk"; 

OFFSET = OUT 10 ns AFTER "clk"; 

 

The timing report (.tim) shows: 

 

TS_clk=PERIOD:clk:10.00: Met 

OFFSET=IN : 10.00: N/A 

OFFSET=OUT : 10.00: N/A 

TS2001=FROM:INT_CLK_clk:TO:INT_TNM_OFFSET_OPAD:10.0: Met 

TS2002=FROM:INT_TNM_OFFSET_IPAD:TO:INT_REG_clk:11.1: Met

Solution

The OFFSET IN and OFFSET OUT constraints have been renamed: TS2001 is the OFFSET OUT and TS2002 is the OFFSET IN. In both cases, the constraints are renamed and rewritten as FROM:TO constraints. The new constraints are correct. 

 

- The OFFSET OUT constraint, written as a FROM:TO constraint, should subtract the clock propagation delay (Tgck). This is corrected in 6.1i Service Pack 2. 

 

- The OFFSET IN constraint, written as a FROM:TO constraint, might be confusing because the offset value has changed from 10 ns to 11.1 ns. The extra delay added to the FROM:TO constraint is due to the addition of clock propagation delay (Tgck). When this is taken into consideration, the new FROM:TO constraint is equivalent to the original constraint. 

 

This issue is fixed in the 6.1i software release.

AR# 14898
Date Created 08/29/2007
Last Updated 05/08/2014
Status Archive
Type General Article