Has anyone noticed parasitic capacitance increased between mpw8 and the latest tools? I'm running ST...

Matt Venn

04/14/2023, 8:53 AM

Has anyone noticed parasitic capacitance increased between mpw8 and the latest tools? I'm running STA on the TinyTapeout design and traces routed on met1,2,3 between blocks has jumped from 0.03 to 0.06

Matt Venn

04/14/2023, 8:53 AM

image.png

Matt Venn

04/14/2023, 8:54 AM

tt02 layout

Matt Venn

04/14/2023, 8:54 AM

tt03 layout

Matt Venn

04/14/2023, 8:55 AM

Passing STA on TT02: https://github.com/TinyTapeout/tinytapeout-02/actions/runs/4588764460

Matt Venn

04/14/2023, 8:55 AM

failing STA on TT03: https://github.com/TinyTapeout/tinytapeout-03/actions/runs/4679824181/jobs/8290379525#step:7:643

Matt Venn

04/14/2023, 8:56 AM

My guess is that the values for capacitance have changed in the newer PDK, but I'm having a hard time testing it because I switched to the new JSON configuration for TT03 and it's making it much harder to try the old PDK and old openlane with the TT03 configuration

Kareem Farid

04/16/2023, 1:09 PM

@Matt Venn is it possible to share both full reports ?

Matt Venn

04/17/2023, 11:38 AM

@Kareem Farid the reports are linked above

Matt Venn

04/17/2023, 11:39 AM

@Jeremy Birch has been helping me with this, and his thoughts are that the parasitics for TT02 were too low

Kareem Farid

04/17/2023, 12:26 PM

@Matt Venn I am suspecting the following: There are differences in the wrapper level routing between TT02 and TT03, such as net

sw_245_clk_out

having differences in capacitances . If we take these variances and high fanout of scanchain blocks into account, they can propagate and lead to what we are seeing now. I will try to confirm this suspicion by tomorrow, as today is a National holiday in Egypt.

Matt Venn

04/17/2023, 1:05 PM

Thanks Kareem. I checked the nets and they looked very similar to me. Also, the fanout is low, as it's just one clock to the next. Max fanout is 1.

Kareem Farid

04/17/2023, 1:16 PM

The fanout of a chain's root buffer is 10. This buffer is linked to chain and perhaps more sensitive towards subtle differences in capacitances of the link between chains. Will confirm tomorrow

Matt Venn

04/18/2023, 10:48 AM

Hi Kareem, just wondering if you made any progress

Kareem Farid

04/19/2023, 3:05 PM

@Matt Venn what are the differences between tt02 and tt03 ? In terms of OpenLane version, generated files, etc ..

Kareem Farid

04/19/2023, 3:09 PM

Can you compare the length of the same net in the two layouts for example

sw_244_clk_out

Kareem Farid

04/19/2023, 3:10 PM

Also can you share the details of extraction off and on the flow?

Kareem Farid

04/19/2023, 4:13 PM

What were the versions used to generate tt02 user project wrapper spef ?

Matt Venn

04/20/2023, 8:35 AM

check the files in the signoff directory for versions of pdk and openlane

2 Views

Open in Slack

Previous Next

What is Linen?

Linen is a search-engine friendly community platform. We offer integrations with existing Slack/Discord communities and make those conversations Google-searchable.