2026-09-06 16:08 UTC
Late last night, I found out one of the issues with my DisplayPort source. It turns out that the 300 µs timeout in the spec is a bit of a... guideline.
The display I'm connected to responded in 307 µs for native writes. My AUX link layer was retrying repeatedly after 300 µs timeouts, and then failing after 7 retries.
The real discovery was that if your firmware writes 0 to the timeout control register, then your AUX link will just retry immediately! Such unexpected behavior 😝
Replies (1)
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@tom_verbeure@mastodon.social 2026-09-06 17:09
@craigjb@fosstodon.org Which tool created those waveforms? (And yes, you can't assume that all DP sources and sinks rigorously conform to that kind of stuff. The HDMI cert requirements are much stricter.)