QEMU: Passing USB Devices Running Fullspeed to VM with EHCI USB Controller Running Lowspeed

QEMU is a powerful virtualization tool that allows you to run virtual machines on your computer. One common use case is to pass USB devices to a virtual machine so that it can interact with them directly. However, there can be compatibility issues when passing USB devices running at fullspeed to a virtual machine with an EHCI USB controller running at lowspeed. In this article, we will explore how to overcome this challenge and successfully pass USB devices to your virtual machine using QEMU.

Before we dive into the solution, let's first understand the problem. USB devices can operate at different speeds, such as lowspeed (1.5 Mbps), fullspeed (12 Mbps), or highspeed (480 Mbps). The EHCI (Enhanced Host Controller Interface) USB controller is designed to handle highspeed devices efficiently. However, when you pass a fullspeed USB device to a virtual machine with an EHCI USB controller running at lowspeed, the device may not function properly or may not be recognized at all.

To overcome this issue, we can use a combination of QEMU's USB redirection and the UHCI (Universal Host Controller Interface) USB controller. The UHCI controller is an older USB controller that supports lowspeed and fullspeed devices.

Here's how you can pass a USB device running at fullspeed to a virtual machine with an EHCI USB controller running at lowspeed:

1. Make sure you have QEMU installed on your computer. You can download it from the official QEMU website.
2. Connect your USB device to your computer.
3. Open a terminal or command prompt and navigate to the directory where QEMU is installed.
4. Run the following command to list the available USB devices:

Replace usb_bus_number and usb_device_address with the appropriate values for your USB device. You can find these values by running the command lsusb in a terminal or command prompt.

Once you run the command, QEMU will start a virtual machine with a UHCI USB controller and pass the USB device to it. The virtual machine will be able to communicate with the USB device even if it is running at fullspeed, while the EHCI USB controller on your host machine will continue to operate at lowspeed.

It's important to note that not all USB devices may be compatible with this setup. Some devices may require specific drivers or may not work at all in a virtualized environment. Additionally, the performance of the USB device may be affected when using a UHCI USB controller instead of an EHCI controller. Therefore, it's recommended to test the setup with your specific USB device to ensure compatibility and performance.

In conclusion, passing USB devices running at fullspeed to a virtual machine with an EHCI USB controller running at lowspeed can be challenging. However, by using QEMU's USB redirection and the UHCI USB controller, you can overcome this issue and successfully use your USB devices in a virtualized environment.