I²C rise time

What it checks

For nets declared as an I²C class, computes the RC rise time from the actual pull-up values and estimated bus capacitance against the mode's specified limit — and tells you the pull-up value that would pass.

Why it matters

I²C edges are made by the pull-ups alone. Too-weak pull-ups into too much capacitance means edges that never reach threshold in time: a bus that drops bits as you add devices or wire length, which everyone first blames on firmware.

How to fix it

Lower the pull-up value (the message computes the target), shorten the bus, or drop to a slower I²C mode. One pair of pull-ups per bus — every added device brought its own, and that's a different bug.

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