USB 2.0 Development and Testing

Host validation

dmesg -w
lsusb -t
cat /sys/kernel/debug/usb/devices
mount | grep -E 'sd[a-z]|usb'

lsusb -t shows whether a device runs at 1.5M, 12M, or 480M. When a high-speed device falls back to full-speed, inspect D+/D- routing, PHY configuration, power, and cable quality first.

Device / Gadget

With UDC and ConfigFS enabled, functions such as ADB, MTP, Mass Storage, RNDIS, ACM, HID, UAC, and UVC can be combined. Android usually manages the gadget through init/vendor scripts; do not manually create a duplicate gadget while those services are active.

ls /sys/class/udc
ls /config/usb_gadget 2>/dev/null
getprop sys.usb.config
setprop sys.usb.config adb

OTG

OTG depends on controller mode, ID/VBUS or Type-C detection, VBUS power, and the role-switch state machine. Changing only dr_mode or usb_port_type is normally insufficient for a complete hardware role switch.

Performance tests

For Mass Storage, distinguish cache effects from real media performance by using sync, sufficiently large files, and both read and write tests. Test RNDIS/NCM throughput with iperf3 while monitoring CPU load.

Common build and flash workflow

cd <ANDROID_TOP>/longan
./build.sh kernel
./build.sh pack

After flashing, confirm the kernel/DTB build timestamp and version so that new changes are not evaluated on an old image.