USB Passthrough does not work

[Michael Reichenbach]

Hi @ all,
I passed a Primux USB II (ISDN) adapter to the virtual machine via USB, the adapter is also recognized correctly and I was able to install the software and drivers. The fax software does not work because when I call the fax number, the "clean" fax tones do not come in, but it rustles and crackles, etc. The Primux adapter works perfectly on a physical PC. I assume that the adapter is not passed cleanly to the virtual host.

Does anyone know how to fix this error or has anyone had experience with it?

Thanks in advance.

 

[Stefan_R]

The bandwidth of pure USB passthrough is limited, since QEMU has to pass the data through userspace first. This is also noticable with high-fidelity audio gear, where USB passthrough of DACs often leads to crackling noises.

You can try to enable USB3 emulation for the device (checkbox in the GUI), this might help even if the device is 2.0 only since it uses a different QEMU code path.

Alternatively, use PCIe passthrough to assign a PCIe USB card to the VM, and plug the adapter into a slot of the card. Sometimes even on-board USB adapters can be used for this, but that heavily depends on the motherboard. PCIe passthrough features almost native latency and throughput, so the adapter should work fine in this scenario.