# XH-HK4401 4-port HDMI USB KVM Switch

<img src="xh-hk4401.jpg" alt="drawing" width="300"/>

This KVM is [sold](https://www.aliexpress.com/item/4000849336545.html) under many names, and comes in two versions.
The only way these two versions differ is that one has one of its USB ports replaced with a PS/2 port. The
identifying feature is that they come with a small external control unit with 4 buttons. This controller is
connected to the main KVM via a micro USB cable, however this is **NOT** as USB connection.

!!! warning
    Audio was not tested, it is assumed to be non-functional


## Connections

1. Connect the USB-A cable from the Raspberry Pi OTG port to to any of the USB ports on the XH-HK4401 switch. All 3/4 USB ports work exactly the same, internally they are just connected to a USB HUB.

2. Connect the HDMI out from the XH-HK4401 switch to the Raspberry Pi CSI-2 to HDMI input.

3. Connect host USB and HDMI cables from the XH-HK4401 switch to the machines to be managed per the switch instructions.

4. Finally see below for details about connecting to the control micro USB port. **This it not a normal USB micro port.**

!!! warning
    There is a limitation in the underlying PiKVM software related to plugging video cables from a host which is already powered and connected to a monitor to a Raspberry Pi HDMI-CSI bridge. These limitations apply equally when using the XH-HK4401 KVM switch. If video is not present in PiKVM, try keeping all host machines off and connecting them directly to the XH-HK4401 switch before powering the hosts on.


## RS-232 control cable

The control unit communicates to the KVM using the RS-232 protocol (at 5v) not USB, and one of the following
solutions must be used.

### Inverting USB UART adapter (FT-232) - The easy way

Some USB UART adapters have the rare feature to invert the logic level of the RX/TX signals. For example the FTDI FT232 can
be configured via the FTDI configuration GUI to do this. With such an adapter, the circuit above is not required. All you
need is to connect it to a micro-USB connector.

!!! warning
    These options will only work on UART adapters with **genuine** FTDI chips. There are a lot of cheap fakes on the
    market that either lack this option, or will prevent you from changing the settings. To avoid getting a fake
    ensure you always purchase from a reputable store and brand (Adafruit, Sparkfun, etc.), Amazon **is not** a
    reputable store.

### Linux Instructions

??? note "References I used to get my FTDIs working:"
    * https://waterpigs.co.uk/articles/ftdi-configure-mac-linux/
    * https://manpages.debian.org/testing/ftdi-eeprom/ftdi_eeprom.1.en.html
    * https://manpages.ubuntu.com/manpages/bionic/man1/ftdi_eeprom.1.html
    * http://developer.intra2net.com/git/?p=libftdi;a=blob;f=src/ftdi.h
    * http://developer.intra2net.com/git/?p=libftdi;a=blob;f=src/ftdi.c
    * http://developer.intra2net.com/git/?p=libftdi;a=tree;f=ftdi_eeprom
    * http://developer.intra2net.com/git/?p=libftdi;a=blob;f=ftdi_eeprom/example.conf
    * http://developer.intra2net.com/git/?p=libftdi;a=blob;f=ftdi_eeprom/main.c

!!! warning
    Steps were performed on Debian-like installation (Pop!_OS 21.10)

This workflow has worked for a self-described NON-genuine FTDI FT232RL chip. The other MAY be genuine, but it is also working.

Neither of the following FTDI UART adapters are recommended. Purchasing both chips was an error (only 1 intended). However, having two (potentially non-genuine) FTDI UART adapters helped to create these instructions.

- [Possibly genuine, but working regardless, (DSD TECH) FTDI](https://amazon.com/dp/B07BBPX8B8)

- [Not genuine (HiLetGo) FTDI](https://amazon.com/dp/B00IJXZQ7C)

!!! warning 
    The HiLetGo UART adapter comes with a USB MINI female connector and necessitates another adapter/cable for interfacing with the Pi.

1. ??? note "Get info from FTDI"
    * Plug the FTDI into a USB port on your Linux device and run `lsusb` to verify that the device is found
        ```
        lsusb
        ```
    * Ensure the device is recognized as FTDI
        ```
        sudo lshw | grep -B 10 ftdi
        ```
    * Record hardware information (not sure if needed, but was saved to prevent overwriting critical data in the EEPROM)

2. ??? note "Blacklist ftdi_sio kernel module"
    * The kernel module ==ftdi_sio== is currently enabled (and how you saw the device in the previous step). We need to disable this module to read/write to the EEPROM.
    * The following command creates a file to blacklist the ==ftdi_sio== module.
        ```
        echo "blacklist ftdi_sio" | sudo tee /etc/modprobe.d/bl-ftdi.conf > /dev/null
        ```

3. ??? note "Reboot machine"
    * We need to reboot into an environment without ftdi_sio active.
        ```
        shutdown -r 0
        ```

4. ??? note "Install ftdi_eeprom if not already installed"
    * Install ==ftdi_eeprom== with the following command.
        ```
        sudo apt install ftdi_eeprom
        ```

5. ??? note "Make a folder to work from and change it to our working directory"
    ```
    mkdir ./ftdi_config
    cd ./ftdi_config
    ```

6. ??? note "Create a valid FTDI configuration file for ftdi_eeprom consumption"
    * The below command (copy/paste all lines) will create a valid configuration file. Change parameters as required.
        ```
        tee ./ftdi.conf > /dev/null <<EOF
        filename=eeprom.bin
        vendor_id=0x0403
        product_id=0x6001
        manufacturer="FTDI"
        product="FT232 Serial (UART)"
        serial="SERIAL"
        use_serial=true
        max_power=500
        self_powered=false
        invert_txd=true
        invert_rxd=true
        cha_type="UART"
        EOF
        ```
    * This configuration is trimmed from the example due to size of the EEPROM on the FTDIs used.
    * The example configuration at ==/usr/share/doc/ftdi-eeprom/example.conf== describes possible configuration options for the FTDI and is well-documented.
    * The above configuration worked for the mentioned devices. The ==filename==, ==vendor_id==, ==product_id==, ==invert_txd==, and ==invert_rxd== variables are required. The others might not be, but seemed applicable.
    * If you're using a different FTDI chip than used here, please update that in the above configuration. Ensure that vendor_id and product_id are what was obtained from the output of the initial `lsusb` command.
    * ==max_power==, ==serial==, and ==product== were updated to reflect the output of the initial `lshw`. These updates may not be required and were done to avoid overwriting anything important. ==cha_type== was updated to ==UART== where both of the devices were originally designated as FIFO.

7. ??? note "Test the configuration and read the eeprom initially before flashing"
    * Read the EEPROM with the following command
        ```
        sudo ftdi_eeprom --read-eeprom ./ftdi.conf
        ```
    * If you get an error here, there's something wrong with your configuration. Check that the device is properly identified and try again.

8. ??? note "Rename/preserve and review the contents of the binary read from the EEPROM"
    * First, rename the output binary file so we don't overwrite it when we flash (flashing writes the flashed binary to the ==filename== path)
        ```
        mv ./eeprom.bin ./original_eeprom.bin
        ```
    * Then, display the outputs of the binary
        ```
        hexdump -C original_eeprom.bin
        ```
    * You can rename the binary in the configuration file by editing the ==filename== variable. If you can't be bothered to edit the file, rename it as detailed above.

9. ??? note "Flash the configuration"
    * Run the following command to flash the EEPROM of the FTDI
        ```
        sudo ftdi_eeprom --flash-eeprom ./ftdi.conf
        ```
    * Optional: compare the flashed configuration to the initial configuration with the below command. If there is no output, the files are the same. You will likely need to re-flash.
        ```
        diff <(xxd original_eeprom.bin) <(xxd eeprom.bin)
        ```
    * Alternatively, you can manually compare the files by running `hexdump -C original_eeprom.bin` and `hexdump -C eeprom.bin`

10. ??? success "Your FTDI should be flashed and working to control the KVM!"
    - Plug it into one of the Pi's USB slots (if not already), and it's good to go.
    - The KVM will sink power from the FTDI (Pi) if Vcc is connected. If Vcc is disconnected, ensure that grounds between the Pi and KVM are tied.

11. ??? note "Clean up the ftdi blacklist to reenable the ftdi_sio module"
    * Comment out the line but leave the file with the following command:
        ```
        sudo sed -i 's/blacklist ftdi_sio/#blacklist ftdi_sio/g' /etc/modprobe.d/bl-ftdi.conf
        ```
    * If you'd need to read/flash FTDI EEPROM in the future, you can use the following command (followed by a reboot) to blacklist the ==ftdi_sio== module again.
        ```
        sudo sed -i 's/#blacklist ftdi_sio/blacklist ftdi_sio/g' /etc/modprobe.d/bl-ftdi.conf
        ```
    * If you want to wash your hands of FTDI flashing, then delete the blacklist file with the following command:
        ```
        sudo rm /etc/modprobe.d/bl-ftdi.conf
        ```

12. ??? note "Reboot the machine to reset to initial state (with ftdi_sio loaded)"
    * ==ftdi_sio== should reload as the driver, and the FTDI should be able to be seen with `lshw` / `dmesg` once again. If you tried to run either command while ==ftdi_sio== was blacklisted, you probably would have come up empty.

### Windows Instructions

In order to invert the RX/TX signals, you can use [ft_prog](https://ftdichip.com/utilities/#ft_prog) and set the 
following settings:

<img src="ft232_config.png" />

Once the UART is configured, please fully disconnect it and connect it back to the computer. Relaunch `ft_prog` and ensure the settings are still set. If they are not, you have a *fake* FTDI chip.

### FTDI Terminal Configuration

Finally, you will need to connect it to the micro USB port (**This it not a normal USB micro port.**)
like so:

| Signal | Colour | FT232 Pin                                           |
| ------ | ------ | --------------------------------------------------- |
| Vbus   | Red    | 5v (if you want to power the KVM from the Pi's USB) |
| D-     | White  | RX                                                  |
| D+     | Green  | TX                                                  |
| Gnd    | Black  | GND                                                 |


### An inverter circuit - The cheap way

For this you will need:

* 1x 74HC14
* 1x USB A socket, or sacrificial micro USB cable
* Optional 1x Diode - If you want to power the KVM from the Raspberry Pi
* 1x 5-pin header
* 5x Female - Female jumper cables

<img src="xh-hk4401_circuit.png" />

!!! note
    Please search online for USB pinouts to ensure you connect it properly.

## Adding UI elements to control the KVM switch

The UI can be updated to add buttons to switch between KVM inputs and indicators for which input is currently selected.  The instructions below will make these available in the PiKVM UI after clicking the "GPIO" menu button in the KVM view.

1. SSH into PiKVM

2. Enable read-write mode on the sd card via `rw`

3. Edit the `/etc/kvmd/override.yaml` file and include the following. 

   | Method   | Device         |
   |----------|----------------|
   | FT-232   | `/dev/ttyUSB0` |
   | Inverter | `/dev/ttyAMA0` |

   ```yaml
   kvmd:
       gpio:
           drivers:
               hk:
                   type: xh_hk4401
                   device: /dev/ttyUSB0
           scheme:
               ch0_led:
                   driver: hk
                   pin: 0
                   mode: input
               ch1_led:
                   driver: hk
                   pin: 1
                   mode: input
               ch2_led:
                   driver: hk
                   pin: 2
                   mode: input
               ch3_led:
                   driver: hk
                   pin: 3
                   mode: input
               ch0_button:
                   driver: hk
                   pin: 0
                   mode: output
                   switch: false
               ch1_button:
                   driver: hk
                   pin: 1
                   mode: output
                   switch: false
               ch2_button:
                   driver: hk
                   pin: 2
                   mode: output
                   switch: false
               ch3_button:
                   driver: hk
                   pin: 3
                   mode: output
                   switch: false
           view:
               table:
                   - ["#Input 1", ch0_led, ch0_button]
                   - ["#Input 2", ch1_led, ch1_button]
                   - ["#Input 3", ch2_led, ch2_button]
                   - ["#Input 4", ch3_led, ch3_button]
   ```

4. Return to read-only mode for the sd card via `ro`

5. Restart the kvmd service: `systemctl restart kvmd`


## Switching between hosts in the UI

To switch between hosts, enter the KVM UI and click the "GPIO" menu. You should see 4 inputs, one of which will have a green circle indicating it is currently selected. Click the other inputs to change the selected host.
