So, I'm getting a bunch of slew rate warnings from...
# openlaneo
Olof Kindgren
12/28/2021, 7:01 PMSo, I'm getting a bunch of slew rate warnings from the finished build, like
Copy code
Pin Limit Slew Slack
------------------------------------------------------------
_20535_/A 1.50 2.21 -0.71 (VIOLATED)
_20164_/A 1.50 2.21 -0.71 (VIOLATED)
_20901_/A 1.50 2.21 -0.71 (VIOLATED)
_21281_/A 1.50 2.20 -0.70 (VIOLATED)
_23513_/A 1.50 2.20 -0.70 (VIOLATED)
_23143_/A 1.50 2.20 -0.70 (VIOLATED)
_21649_/A 1.50 2.20 -0.70 (VIOLATED)
ANTENNA_372/DIODE 1.50 2.20 -0.70 (VIOLATED)
_22759_/A 1.50 2.20 -0.70 (VIOLATED)
_22020_/A 1.50 2.20 -0.70 (VIOLATED)Matt Venn
12/28/2021, 7:10 PMThis is all I know about it
o
Olof Kindgren
12/28/2021, 7:14 PMMy first guess would be a slow slew rate being caused by a high fanout, which could potentially be fixed on the design side with an RTL change or forced buffer insertion. But I still have no clue where this is
Olof Kindgren
12/28/2021, 7:15 PMI know where pretty much every FF is in the design so I'm right now considering to follow the synthesized netlist to see where it starts to look familiar
Olof Kindgren
12/28/2021, 7:17 PMOnce again cursing the lack of a decent FOSSi netlist viewer
m
Matt Venn
12/28/2021, 7:19 PMYou should be able to find it with klayout, magic or openroad gui
Matt Venn
12/28/2021, 7:19 PMBut I couldn't tell you how
o
Olof Kindgren
12/28/2021, 7:19 PMOh, I thought those only had layout viewers
m
Matt Venn
12/28/2021, 7:19 PMBut they know the names of the nets
k
Kunal
12/28/2021, 7:19 PMYou can print "net", "fanout" and "load" values in this report. This will report which is the exact net where you see huge load capaitance
Once you get that, view that net using klayout or magic. May be it's a long net with no high fanout synthesis done
Kunal
12/28/2021, 7:21 PMcommand should be report_checks -through <cellname>/A -fields {.....}
Something similar, where in "-fields" switch, you should be able to put "nets", "fanout", etc....
o
Olof Kindgren
12/28/2021, 7:23 PMThanks @User
m
Maximo Balestrini
12/28/2021, 11:13 PMI definitely recommend using OpenROAD gui to debug this things (you'll have to download OpenROAD and compile it).
You can search nets & instances by name and then follow their inputs/outputs
I've also created a repo with some openroad scripts to help with loading openlane or caravel results (including the timing reports). They are a bit messy but they do their job:
https://github.com/mbalestrini/openroad_useful_scripts
o
Olof Kindgren
12/28/2021, 11:21 PMThanks @User That does sound very useful.