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AR# 42701

13.3 Timing Analyzer/TRCE - OFFSET hold path analysis is incorrect when no VALID value is specified

Description

The hold path offset calculation in the timing report is as followingwhen no valid value is specified in the OFFSETIN constraint:

Offset (hold paths): -1.863ns (data path - clock path + uncertainty)
Source: LVDS_TL_DAT0_P (PAD)
Destination: AD9970_TL/DOUT0_A_IDDR (FF)
Destination Clock: lvds_tl_clk rising at 0.000ns
Data Path Delay: 1.970ns (Levels of Logic = 2)
Clock Path Delay: 3.858ns (Levels of Logic = 2)
Clock Uncertainty: 0.025ns

The OFFSET(hold paths) calculation (data path - clock path + uncertainty) is not a hold time calculation, butrather, it is a setup time calculation.

What is the problem here?

Solution

When no valid value is specified in the OFFSET IN constraint, the hold time check is not performed.What is being reported instead is actually the fast path setup calculation (at the slow corner), not a hold calculation. So, here the report header [Offset (hold analysis)] does not match the calculation. The correct report header should be [OFFSET (fast setup paths)].

When a valid value is specified in theOFFSETIN constraint, the hold slack calculation is correct in the timing report.

(requirement - (clock path + clock arrival + uncertainty - data path))

To resolve this problem, specify theVALID value in the OFFSET IN constraint so thata valid hold check can be performed.

AR# 42701
Date Created 10/10/2011
Last Updated 12/15/2012
Status Active
Type General Article
Tools
  • ISE Design Suite - 13.1
  • ISE Design Suite - 13.2
  • ISE Design Suite - 13.3