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AR# 4415

PPR WARNING 7028: How to set Flagblk CLB_Disable_SR_Q on Flops in Xdelay

Description

Keywords: xdelay, asynchronous, set, reset, path.

Urgency: Standard

General Description:
If your design has flip-flops with asynchronous set/reset,
you might get the following warning from PPR:

*** PPR: WARNING 7028:
The design has flip-flops with asynchronous set/reset
controls (PRE/SD or CLR/RD pins). When PPR analyzes design
timing, it does not trace paths through the asynchronous
set/reset input and on through the Q output.

If you want PPR to control the delay on paths through
asynchronous set/reset pins, you must split the delay
requirement into two segments: one ending at the set/reset
input, and the other beginning at the flip-flop output.
If you want PPR not to analyze paths that lead to
asynchronousset/reset pins, attach an IGNORE specification to
the pin(s) or signal(s).

By default, XDelay reports all paths through
asynchronous set/reset pins. To prevent XDelay from showing
these paths, use FlagBlk CLB_Disable_SR_Q on the appropriate
flip-flops.

How do to set Flagblk on in XDELAY?

Solution

1- Start Xdelay.
2- Load the design_name.lca file.
3- Click on Timing Menu and select Flagblk.
4- It now lists all of the available flags. Select
CLB_Disable_SR_Q
5- It will now list all of the flops in the design.
You can select as many as you want or you can select them
all. Then close.
6- Click on Timing Menu and select Save Template. It will
prompt you for a name and click ok.
7- Then run the analysis in xdelay. To use this flag in the
future simply load the template before analyzing.

AR# 4415
Date Created 08/31/2007
Last Updated 10/05/2008
Status Archive
Type General Article