From 5b2ae2507173d58399293ea62cbf4102d41d8ead Mon Sep 17 00:00:00 2001 From: mikkeli Date: Fri, 9 Oct 2026 00:43:37 +0900 Subject: [PATCH] USB report: the long outages were Android sleep, not the link Idle on battery, the tablet suspends ~60 s after screen-off and only answers at its DHCP-renewal wakeups while the USB link stays up. Kept awake with a video, a PD unplug costs 3.1 s and then nothing. The earlier replug silences were the tablet waking from sleep. Co-Authored-By: Claude Opus 5.5 --- docs/impl/reports/USB-TABLET-LINK.md | 14 ++++++++++++++ 1 file changed, 14 insertions(+) diff --git a/docs/impl/reports/USB-TABLET-LINK.md b/docs/impl/reports/USB-TABLET-LINK.md index 87b1002..4c3b5dd 100644 --- a/docs/impl/reports/USB-TABLET-LINK.md +++ b/docs/impl/reports/USB-TABLET-LINK.md @@ -111,6 +111,20 @@ Three PD unplug/replug cycles while pinging the tablet every 0.5 s: - Exact replug time isn't known; the first failed ping is used as its marker. - Repeat (plug-in at ~00:27:12): the tablet was silent for 7.8 s with the Orin's link up, then one gadget reconnect (00:27:25.1–27.0) and a fresh `DHCPDISCOVER`; about **15 s** to stable. Replug consistently costs more than unplug (3.5 s). +#### The "silence" is Android sleeping, not the link + +| Test (2026-10-09) | Tablet state after PD unplug | Result | +|---|---|---| +| Idle, 3 min window | screen times out | Clean for ~60 s, then pings answered only in brief bursts right at its 30 s DHCP renewals, then silent. **No kernel link events**: USB stayed up throughout | +| Video playing, 150 s window | kept awake | 3.1 s outage at the unplug, then **zero loss for 2 min+** | + +- Off charger and idle, Android suspends about 60 s after the screen times out ("keep awake on charge" no longer applies). The USB gadget link + stays electrically up, but the tablet only wakes for timers (DHCP renewal every ~30 s). +- The earlier "replug silence" was the same thing. Those windows started with the tablet already asleep, so plugging power in woke it, and the + 5–8 s was wake-up plus re-creating its USB network. +- So the hub's PD change costs **~3.5 s** (the unplug detach). Everything beyond that came from tablet sleep. +- To the Orin, a sleeping tablet is indistinguishable from a dead link, except by heartbeat. + - At ignition, accessory power drops during cranking, so a start is likely to produce both edges back to back (not tested in the car yet). Consequence: in the car, expect a link outage of up to about 12 s at every ignition change. That is a requirement for the services