( ESNUG 280 Item 1 ) ------------------------------------------------ [2/12/98]

From: "Anders Nordstrom" <andersn@nortel.ca>
Subject: Subtle Alignment Problems In ECO Compiler With Scanned Designs

John,

I have been working with Synopsys new ECO compiler for a while and I found
some strange behaviour by the tool.  I am doing an ECO to a scan inserted
netlist and the eco_align_design command fails sometimes.  The same number
of registers exists in both designs so that is not the problem.

When runnign eco_align_design it reports:

  NOTHING TO REPORT!
  ALIGNMENT COMPLETE!!

This to me indicates that it worked fine but, oh no, it is followed by:

  Error: Alignment not complete. Must use eco_align_design command. (ECO-95)
  Error: Complete alignment of all ports & registers not satisfied. (ECO-83)

The problem turned out to be that two registers called TTR_CS_reg[4] and
TTR_CS_reg[5] were using the same type of flip flop but with different
drive strength.  As far as I know this is only a problem when working with
scannable flip flops.

Solution: manually align the two registers with the commands:

    set_eco_align cell TTR_CS_reg[4] TTR_CS_reg[4]
    set_eco_align cell TTR_CS_reg[5] TTR_CS_reg[5]

  - Anders Nordstrom
    Northern Telecom Ltd.        Ottawa, Canada