usbip client emulation

[pixel4696]

Can esp32 be used as a usbip client emulator (instead of server) which allow user to plug a device into a host?

I would like to use a pair of esp32 to make a wireless USB cable. This would be useful if usbipd server is not compatible with the client device

[yunsmall]

I think the roles are flipped here — in USB/IP, the host machine (the one using the device) is always the client. The client side is the vhci driver: Linux has it built-in (vhci-hcd, driven by the usbip attach command), Windows has it in usbip-win/usbipd. So your host doesn't need an ESP32 to "emulate a client" — it already is one out of the box.

For the wireless-USB-cable use case, the ESP32 should be the server:

1. Plug the physical device into the ESP32's USB-host port
2. Run this project (usbipdcpp_esp32) on the ESP32 — it enumerates the device via libusb and exports it over USB/IP
3. On the host (Linux or Windows), just run usbip attach -r <esp32-ip> -b <busid> — the device appears as if plugged in locally, with no extra software on the host

As for the "usbipd not compatible" pain point: if the reason is a usbipd-win-specific limitation, a server implemented on the ESP32 may be able to export the device where usbipd-win can't — worth testing on your specific device.

[pixel4696]

Thanks for the reply.

Do you happen to know any esp32 usbip client project that I can try?

[yunsmall]

Hi @pixel4696,

I did a quick survey of GitHub for ESP32 usbip client projects. Short answer: I couldn't find any public ESP32 client-side implementation — every ESP32 USB/IP project out there is a server that exports locally attached devices:

• chegewara/esp32-usbip-poc (ESP32-S2/S3 PoC)
• DatanoiseTV/usbip-esp32p4 (ESP32-P4 + OTG)
• huynle/usbip_esp32 (S2/S3 PoC)
• gautam-dev-maker/esp32_usb_repeater (ESP32-S2)
• adafruit/esp-usbip-bridge (P4/S3, control EP0 only so far)

Client implementations only exist on platforms that can run a real USB stack with a virtual host controller: Linux (vhci-hcd), Android (trevd/android_external_usbip), Windows (usbip-win2, the successor of the now outdated usbip-win).

Why is that? A usbip client is essentially a virtual host controller (vhci) — it presents remote devices as if they were on a local USB bus. On ESP-IDF, the USB Host stack is built around a single physical HCD (the DWC OTG controller): the HCD interface is a private header (components/usb/private_include/hcd.h) with no registration mechanism, so there is no supported plug-in point for a virtual HCD today.

That said, with the help of Claude Code I dug into the IDF v5.5 USB stack source and the abstraction is clean enough that a vhci is implementable: the host stack (usb_host.c / usbh.c / hub.c) only talks to the HCD through that device-agnostic interface (port state machine, pipes, URB queues), and you can swap the DWC implementation out via a project-level components/usb override (project components take precedence over IDF built-ins, no IDF source changes needed). The main work is simulating port timing (reset/enumeration) and mapping URBs to USB/IP CMD_SUBMIT / RET_SUBMIT over TCP. Device speed is available from the OP_REP_IMPORT response, so the vhci port speed can be reported correctly.

So: if you just want the wireless-USB-cable effect, this very project (usbipdcpp_esp32) is a server — run it on the ESP32 and usbip attach on your host, no extra client software needed. If you specifically need the ESP32 to attach to a remote device, there's no ready-made project, but it is implementable with the approach above.