Improve global router for asap7/ethmac_lvt where it fails with a single DRC error

[oharboe]

Description

In The-OpenROAD-Project/OpenROAD-flow-scripts#2694 asap7/ethmac_lvt fails global route with a single DRC error after 100 iterations.

To reproduce untar and run https://drive.google.com/file/d/1XCfVGa0DHAz5MO_pJwR_VE8qOhZ1oqoO/view?usp=sharing

No luck in whittling down the problem with deltaDebug.

Suggested Solution

Improve global router.

Additional Context

No response

[maliberty]

The IO pin placement is totally different than master which has few pins on the e/w edges.

[oharboe]

The IO pin placement is totally different than master which has few pins on the e/w edges.

This is unsurprising to me: a completely different optimal solution can be found with tiny differences in initial conditions.

So what does this mean practically?

• Pin ppl chooses a pin placements that is never going to work in global routing and it should have done better, so fix ppl?
• There's nothing wrong here with ppl, nor grt, just lock down pin placement in ORFS test cases in git to avoid random changes breaking master?
• Wait for initial conditions to change again slightly, then merge synth: nudge .rtlil towards cleaner and more canonical OpenROAD-flow-scripts#2694 ?

I ran out of imagination w.r.t. suggesting alternatives :-)

[maliberty]

I think it is worth a bit of digging to see if this is just the flap of the butterfly's wings or something more interesting.

[oharboe]

I think it is worth a bit of digging to see if this is just the flap of the butterfly's wings or something more interesting.

I suppose the test case is somewhat interesting independent of The-OpenROAD-Project/OpenROAD-flow-scripts#2694