lowRISC / lowRISC/ibex

Consider clear-dominant fetch FIFO payload updates

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SystemVerilog
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Description

Local synthesis identifies fetch FIFO payload/error updates on the
taken-branch redirect path. Qualifying their enables with `!clear_i`
improves arrival time from 2.89 ns to 2.77 ns at a measured 0.44% area
cost.

The change has passed directed clear/push/pop testing, Ibex hello_test,
and a standalone SymbiYosys/Z3 proof.

Would this timing/area tradeoff and implementation-level payload
stability behavior be considered appropriate for an upstream RTL change?

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  3. Fork the repository and make your change on a branch.
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Research direction

No RTL file is named. Start by locating the fetch FIFO payload and error updates on the taken-branch redirect path, then review the directed clear/push/pop tests, Ibex hello_test, and the standalone SymbiYosys/Z3 proof. Done means the proposed enable qualification is evaluated for timing, area, payload stability, and upstream suitability.

Written by the indexing model from the issue text.

Assessment

Domain
embedded-iot, performance
Issue type
Feature
Difficulty
4/5
Estimated time
3-5 days
Activity status
Active
Clarity
Mostly clear
Newbie friendliness
48/100

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