intent/strap-address-collision

Remedy ¶

Re-strap one of the two devices to a free address, taking the address map from each part’s datasheet rather than from the schematic.

What it checks ¶

It reports two declared strap groups on the same bus that encode the same number, meaning two devices answering to one address.

For hardware engineers ¶

Of all the checks, this one most needs to be a rule rather than a reviewer.

Each strap is individually correct. Every resistor is the right value, on the right net, pulling the right way. Nothing on either page of the schematic looks wrong, because the fault lies in the relationship between two parts that are drawn separately and reviewed separately.

On the bench it does not present as a strap problem either. Two devices drive the bus whenever either is addressed, so it reads as noise, marginal timing, or an intermittent peripheral. People chase signal integrity for a long time before they suspect an address.

Undecidable groups are excluded, deliberately ¶

When a group’s encoded value could not be read, the rule never decodes it with its missing bits assumed. Every pair it belongs to reports not-considered, naming the half that could not be read and why.

Without that guard, an invented address could invent a collision. A report could then confidently claim that two innocent parts clash. That is worse than saying nothing, because it sends someone to re-spin straps that were correct. Those groups are already reported inconclusive by their own strap-group rule, so the gap is visible rather than silent.

When a group is undecidable, declare its default level so the value can be read. That also clears the inconclusive.

When this rule exists at all ¶

It is compiled only when at least two declared groups share a bus. Below that a collision is not expressible. A rule that could never fail would let a review item bound to it read pass with nothing tested.

Fixing a finding ¶

One of the two devices needs a different address. Check both parts’ strap tables before moving a resistor. Each part can usually take only a constrained set of addresses, and sometimes only one of the two has any freedom.