Post #4249427
2026-07-30 18:35 UTC
Fun engineering challenge if anyone has ideas:
The DisplayPort auxiliary channel appears to reuse opcodes for request and completion packets, and uses generally the same framing. This means that, to a first order, if you have a single packet, or a capture that starts in the middle of a long burst of transactions and don't know if you are at an even or odd packet boundary, it is not trivially possible to unambiguously decode the traffic.
Is there a heuristic that you can apply to the first few packets in a capture to determine which one is a request vs a completion and correctly phase the capture?
Replies (1)
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@azonenberg@ioc.exchange 2026-07-30 18:38
Right now the decode in ngscopeclient simply assumes the first packet in a waveform is a request, the next is a completion, and so on. But if you are capturing in the middle of a large burst of activity, this is going to be wrong and give nonsense 50% of the time on average.