feature: support RTL2GDS flow for no clock design

[Emin017]

Self checks

• I have searched existing issues, including closed issues.
• I have read the documentation and development guide.
• This is a feature request, not a bug report or usage question.
• I have described the workflow need before proposing a solution.

Affected area

Flow/runtime

Problem or workflow need

ECC should support RTL2GDS flow for no clock design.

Proposed solution

• Add sdc for non-clock design
• Skip CTS stage in RTL2GDS flow

Alternatives considered

No response

Examples, command sketches, or references

No response

Are you willing to contribute this feature?

Yes, I can submit a PR.

Additional context

No response

[plitenh]

I'd like to propose a concrete modification strategy for no-clock RTL2GDS support, and I'll keep the PR focused on flow-level changes (skip CTS, accept minimal SDC, adjust checklists/signoff, and add regression coverage) while leaving placement/routing/core algorithm changes out of scope.

[plitenh]

To visualize the program flow for no-clock support, I've sketched a diagram that covers the key decision points

[Emin017]

@plitenh Hi, welcome and thanks for the PR contribution!

However, could you add support based on the more complex SDC in this PR? The current SDC support on the ecc main branch is a bit too basic — we need to be able to set I/O delays and a range of other constraints.

[plitenh]

@plitenh Hi, welcome and thanks for the PR contribution!

However, could you add support based on the more complex SDC in this PR? The current SDC support on the ecc main branch is a bit too basic — we need to be able to set I/O delays and a range of other constraints.

In a follow-up PR I’ll land a minimal scaffold that (1) documents test-layer boundaries against this repo’s existing practices (pytest, coverage, and Z3 formal under test/formal/),
and (2) stubs any missing pieces we discussed (e.g. smoke). Formal/Z3 work will extend the current harness, not replace it; fuller smoke/coverage policy and more invariants can
come after. The layer we discussed are useful and are already reflected in that plan.