Serial: legacy UART vs UEFI serial

source/hardware/bios.rst

@@ -126,7 +126,7 @@ Make note of it so you can compare it to the new version to verify everything we
 **Step 7**
 
 Go to Setup Utility --> AMD CBS --> FCH Common Options --> UART Configuration Options --> UART 0 Legacy Options.
-Make sure this setting is set to **Disabled**.
+Make sure this setting is set to **Disabled**. This is explained in :ref:`legacy_uart`.
 
 .. note::
 

source/hardware/serial_connectivity.rst

@@ -17,3 +17,17 @@ Supplied with the firewall is a mini-usb to usb cable, use this to connect the t
 next start your terminal program (Putty, screen, etc).
 
 The baudrate should be set to :code:`115200,8N1`
+
+.. _legacy_uart:
+
+**Legacy UART vs. UEFI serial**
+=====================================================================================================================
+
+Starting from OPNsense 22.1 (22.4 for the business edition), support for legacy serial UART0 communication is dropped, 
+since the upgrade to FreeBSD 13-STABLE required a switch to the UEFI serial protocol.
+Prior to this, only legacy serial UART0 was possible. Should you connect your Deciso appliance with a serial line 
+and get limited output / no output from the point of handover to the OS, it is important your BIOS settings are updated 
+to disable legacy UART.
+
+While in the BIOS, go to Setup Utility --> AMD CBS --> FCH Common Options --> UART Configuration Options --> UART 0 Legacy Options.
+and make sure this setting is set to **Disabled**.