app-flutter/docs/ADB-IN-CAR.md

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ADB in the car

In one line: ADB over TCP on the tablet's USB-Ethernet link to the Orin, reached from halogen through one SSH port-forward via the Orin. TCP mode is armed once over a USB cable to halogen, and again after every tablet reboot.

Why USB debugging is unavailable in the car

A USB link has exactly one host and one device. The tablet's single USB-C port can be either, decided by the USB-C CC resistors at plug-in:

Plugged into	Tablet role	USB debugging
halogen	device	yes: ADB is a USB function the tablet offers as a device
the Orin (via the PD hub)	host	no: a host offers no USB functions

A data hub does not help: it adds more devices under the same host. The PD hub in the car only passes power through, so the tablet charges while it is the host.

What the link is

The Orin runs Jetson's USB device mode (l4t-usb-device-mode) and presents itself as a USB network adapter, with a DHCP server on it. The tablet's kernel binds it as NCM and Android brings it up as an ordinary Ethernet network:

tablet 192.168.55.100  ⇄  USB NCM  ⇄  Orin 192.168.55.1

The app reaches svc-gw over this network. It requests the network explicitly and binds to it, because a network without internet never becomes Android's default while WiFi or LTE is up. adbd is a system daemon and needs none of that: once it listens on TCP, it listens on every interface, this one included.

The path from halogen

halogen is not on 192.168.55.0/24; the Orin is. halogen reaches the Orin over the LAN or the tailnet (the Orin has an LTE uplink), so one SSH local forward bridges the gap:

adb (halogen) → localhost:15555 ═SSH═▶ Orin → 192.168.55.100:5555 → adbd (tablet)

Authorisation is unchanged: the tablet still checks ADB's RSA key, and halogen's key was accepted at the USB pairing. The tablet's port is reachable only from the NCM link (and from WiFi, while TCP mode is on and WiFi is up).

Steps

1. Arm, at the desk (USB cable to halogen; once per tablet boot):

adb -s 1f1530c87d84 tcpip 5555

2. In the car (tablet on the Orin, app link up):

ssh -N -o ExitOnForwardFailure=yes -o ServerAliveInterval=10 \
    -L 15555:192.168.55.100:5555 mikkeli-orin-nano &
adb connect localhost:15555
adb devices                               # → localhost:15555  device
flutter run -d localhost:15555 --dart-define=YUKART_GW=ws://192.168.55.1:7700/

The default gateway address already is ws://192.168.55.1:7700/; the define only matters if a desk build was installed last.

3. Disarm (optional): adb usb returns ADB to USB only. A reboot does the same.

Local port 15555, not 5555: halogen's adb server scans localhost 5555–5585 for emulators, and a tunnel there shows up a second time as emulator-5554.

When it does not work

Symptom	Check
connect refused or times out	From the Orin: nc -zv 192.168.55.100 5555. Refused means TCP mode is off: the tablet rebooted; re-arm over USB
No route to 192.168.55.100 from the Orin	The USB link is down: cable, PD hub, or the tablet asleep (see the initial plan, "The USB link, as measured")
unauthorized	Accept the prompt on the tablet; the halogen key was revoked or never accepted
bind: Address already in use on 15555	An old tunnel is still running: pkill -f 15555:192.168.55.100

Alternatives

• adb on the Orin itself. adb connect 192.168.55.100:5555 there, no tunnel. Needs adb installed on the Orin, and flutter run stays on halogen anyway.
• Wireless debugging (Android 11+, pairing codes) survives better, but it only runs over WiFi, so it does not use this link.

Status (2026-10-11)

Tested with the tablet on the Orin, charging through the PD hub:

• Works: adb tcpip 5555 on HyperOS, the SSH forward, adb connect, shell, input, screencap. The app retargeted to ws://192.168.55.1:7700/ showed USB link up, bound, the Orin's gateway with no mock banner, and a mark reached the recorder (answered no session, correctly, with no CAN traffic).
• Bulk transfer does not. The NCM link loses packets under load: ping loss rose from 0% at 5 packets/s to as much as 32% at 20 packets/s, mostly small packets, with no error counted on the Orin's side. TCP backs off (RTO ~10 s), and throughput collapses to ~54 kB/s. A 20 MB push took 6 minutes. The 165 MB debug APK install failed, and so will flutter run's first install. The app's own traffic (small, 5 Hz) is unaffected so far.

The PD hub causes the packet loss. With the tablet on a plain C-to-C cable straight to the Orin, ping loss is 0% at every size, even at 100 packets/s, and a raw one-way TCP transfer Orin → tablet runs at ~4.3 MB/s with 4 retransmits in 20 MB.

adb push is still slow without the hub: ~0.14 MB/s, 175 retransmits in 20 MB, against 4 for the raw transfer. Cause not found. A bulk transfer running beside a ping burst loses nothing, so it is not simply traffic in both directions.

Until both are understood, install at the desk over USB, and use the car path for logcat, shell and screenshots. The car still needs the PD hub to charge the tablet, so the hub, or its replacement, needs its own test.

A test trap: commands started from adb shell on the tablet use Android's default network (WiFi), not the USB link. nc 192.168.55.1 … from there gets no route. Only sockets bound to the Ethernet network, as the app's are, take the link.