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Link drops: PD change costs ~3.5 s; app must keep the tablet awake

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Further USB tests showed the 5-15 s outages were Android suspending on
battery, not the hub. Kept awake, a PD unplug costs ~3.5 s. Adds the
requirement that the app keeps the tablet awake while it is the display,
and notes a sleeping tablet is invisible to link state.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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mikkeli
2026-10-09 00:43:38 +09:00
parent 6300006859
commit 3422b084ac
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@@ -147,16 +147,21 @@ re-dialling is the client's job. Noticing the loss and redelivering is the Orin'
### Link drops are routine, not exceptional
Measured on the USB path (tablet ↔ PD hub ↔ Orin, 2026-10-09): every PD power
change resets the hub's data port. The link flaps about three times and is back
within 5–12 s, with no intervention. In the car this happens at every ignition
Measured on the USB path (tablet ↔ PD hub ↔ Orin, 2026-10-09): cutting PD power
resets the hub's data port, and the link is back within ~3.5 s with no
intervention. Longer outages measured early on were the tablet sleeping on
battery, not the link. In the car this happens at every ignition
change. Design for it as normal operation. Requirements, not yet implemented:
- **Failure detection on the Orin.** An app-level heartbeat with a timeout of a
few seconds, not TCP alone. A connection on a link that went down can stay
half-open long after the app has re-dialled. Reap dead connections and their
per-client queues promptly. Link state doesn't help either: when PD is plugged back
in, the Orin's interface stays up while the tablet goes silent for ~5 s.
per-client queues promptly. Link state doesn't help either: a tablet that has
fallen asleep on battery leaves the Orin's USB interface up while answering
nothing.
- **The app keeps the tablet awake while it is the display.** Off charger, Android
suspends about a minute after screen-off. Then the link is gone in every way that
matters. Kept awake, a PD change costs only ~3.5 s (measured).
- **Downstream (latest-wins):** unchanged. On reconnect, push current state; no
resend, since stale samples are worthless.
- **Reliable channel (TTS chunks, acknowledgements):** pending items survive a