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USB report: plug-in with tablet awake costs ~2.2 s

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No USB-C detach, one gadget reconnect and a fresh DHCP exchange. With
sleep ruled out, the hub's PD edges cost ~3.5 s (unplug) and ~2.2 s
(plug-in).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
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mikkeli
2026-10-09 00:46:33 +09:00
parent 5b2ae25071
commit b3f1216060
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docs/impl/reports/USB-TABLET-LINK.md
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@@ -117,12 +117,14 @@ Three PD unplug/replug cycles while pinging the tablet every 0.5 s:
|---|---|---| |---|---|---|
| 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 | | 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+** | | Video playing, 150 s window | kept awake | 3.1 s outage at the unplug, then **zero loss for 2 min+** |
| Video playing, PD off → **plugged in** (90 s window) | kept awake | No USB-C detach; one gadget reconnect (link down 0.7 s), fresh DHCP, **~2.2 s** to ping replies, then zero loss |
- 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 - 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). 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 - 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. 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. - So with the tablet awake, the hub's PD changes cost **~3.5 s on unplug** (full detach) and **~2.2 s on plug-in** (gadget reconnect only).
Everything beyond that came from tablet sleep.
- To the Orin, a sleeping tablet is indistinguishable from a dead link, except by heartbeat. - 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). - 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).