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AR# 5747

12.1 Timing/Constraint - Can I place higher priorities on certain constraints in the User Constraints File (UCF)?

Description

Can I place higher priorities on certain constraints in the UCF file?

解决方案

Yes. On path constraints, such as FROM:TO or FROM:THRU:TO, the keyword "PRIORITY" should be used to distinguish between two constraints covering the same path.

For example:

TIMESPEC TS_01= FROM A TO B 10ns;
TIMESPEC TS_02= FROM A TO B 20ns PRIORITY 1;

For more information on the PRIORITY keyword, see the Constraints Guide:
http://www.xilinx.com/support/software_manuals.htm

Different constraints also have different priority levels. The following constraints are listed in order from the highest priority to the lowest priority:

Highest
................0. Timing Ignores (TIGs)
................1. FROM:THRU:TO specifications
................2. FROM:TO specifications
................3. Specific OFFSET constraints (specific data IOB)
................4. Group OFFSET constraints (time group of data IOB)
................5. Global OFFSET constraints (for all data IOBs)
................6. ALLPATHS constraints (such as PERIOD)
Lowest

For more details on timing constraints, please see the Timing Constraints User Guide: http://www.xilinx.com/support/documentation/sw_manuals/xilinx12_1/ug612.pdf

AR# 5747
创建日期 08/21/2007
Last Updated 06/03/2010
状态 Active
Type 综合文章