Lesson Learn
Tweaker Timing Derate Setting
Sample: HLB 13
Project: TPK
1 - Phenomenon
Path Reg to RAMs, check hold timing.
- Abnormal number of HOLD_insertion buffers which are automatically
added by TWK to fix hold violations.
- Delay incr from these buffers are ~400ps (500ps->900ps) -> These delay
incr will affect to setup timing, setup violation pops up after run 1 twk
iteration.
SLACK VIOLATED: -0.009
Data Arrival Time: 987ps.
Data Required Time: 149ns.
Library Hold Time: 148ns.
Slack violated only: -0.009ps.
Comments:
- We found that many hold paths got small violations (<10ps)
- These path are thru/to/from RAMs/ROMs -> Abnormal library
hold/setup time. The diff of Arrival/Required time is very significant,
however, slack violation is very small.
1 - Phenomenon
Abnormal library setup/hold time
Report in tweaker.log file.
Keyword: ^Inconsistency
• Library hold time is increasing significantly. We
can only see in tweaker.log file or TWK GUI.
• In TWK, there are slk_pba_offset which will be
added to re-calculate the slack in report -> small
violation.
Slack after
applied
slk_pba_offset
Slack before
applied
slk_pba_offset
slk_pba_offset
(generated by
TWK tool)
• Tweaker will automatically adding a lot of
DELD/DELF buffers by default setting to fix hold
violations.
1 - Phenomenon
- The POCV (Parametric On Chip Variation) Incremental
Derate were in tweaker environment by SNI’s side.
-> Wrong setting cause to big hold/library setup time.
- Conclusion:
• This issues could be critical if engineer did not
check ECO card which are generated by TWK tool
carefully.
• Adding many hold_insertion buffers which are not
correct function by TWK could lead to roll-back
many eco iterations -> affect to TOP’s result and
the whole progress.
SNI will release setting for
rams/roms separately