Dynamic USB configuration

PiKVM emulates a number of USB devices to ensure normal operation: keyboards, mouse and mass storage drive. Also an additional relative mouse may be present (like on PiKVM V4 by default), or a user configured USB Ethernet or Serial port.

In rare cases, the host BIOS/UEFI may not understand such a large number of emulated devices on single USB port, so some of them may need to be disabled. USB reconfiguration usually requires a reboot, but it is possible to temporarily disable already configured existing emulated devices.

Warning

This feature is experimental. Due to the imperfections of the kernel modules, rarely a dynamic configuration change can lead to a kernel panic and reboot.

For PiKVM V3 and V4 this is considered more secure because they have two independent watchdog systems that can bring devices back to life after a timeout of a few minutes.

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Command-line utility

The kvmd-otgconf utility allows you to view and modify the USB configuration on the fly. It requires root permission and can be used for example from a web terminal.

View the config:

# kvmd-otgconf
+ hid.usb0  # Keyboard
+ hid.usb1  # Absolute Mouse
+ hid.usb2  # Relative Mouse
+ mass_storage.usb0  # Mass Storage Drive

Each line represents a device (function). First comes plus or minus sign (the device on or off), then the name of the device and its description.

Disabling the device:

[root@pikvm ~]# kvmd-otgconf --disable-function mass_storage.usb0
+ hid.usb0  # Keyboard
+ hid.usb1  # Absolute Mouse
+ hid.usb2  # Relative Mouse
- mass_storage.usb0  # Mass Storage Drive

Enabling the device:

[root@pikvm ~]# kvmd-otgconf --enable-function mass_storage.usb0
+ hid.usb0  # Keyboard
+ hid.usb1  # Absolute Mouse
+ hid.usb2  # Relative Mouse
+ mass_storage.usb0  # Mass Storage Drive

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Web UI menu

Using the pseudo-GPIO driver, you can also control devices via the menu in the web interface. Read about GPIO basics here.

To setup the menu, use kvmd-otgconf --make-gpio-config to generate the configuration, and merge it with your existing one in /etc/kvmd/override.yaml in a usual way.

The example of kvmd-otgconf --make-gpio-config output

# kvmd-otgconf --make-gpio-config
kvmd:
    gpio:
        drivers:
            otgconf:
                type: otgconf
        scheme:
            hid.usb0:
                driver: otgconf
                mode: output
                pin: hid.usb0
                pulse: false
            hid.usb1:
                driver: otgconf
                mode: output
                pin: hid.usb1
                pulse: false
            hid.usb2:
                driver: otgconf
                mode: output
                pin: hid.usb2
                pulse: false
            mass_storage.usb0:
                driver: otgconf
                mode: output
                pin: mass_storage.usb0
                pulse: false
        view:
            table:
                - ["#Keyboard", "#hid.usb0", hid.usb0]
                - ["#Absolute Mouse", "#hid.usb1", hid.usb1]
                - ["#Relative Mouse", "#hid.usb2", hid.usb2]
                - ["#Mass Storage Drive", "#mass_storage.usb0", mass_storage.usb0]