Update Ubuntu.md

Signed-off-by: Robin Davies <rerdavies@gmail.com>

docs/Ubuntu.md

@@ -5,15 +5,11 @@ icon_float: left
 ---
 ## PiPedal support for Ubuntu
 
+{% include pageIconL.html %}
+
 PiPedal will run on Ubunut 24.x (both aarch64 and amd64/x64) as well as Raspberry Pi OS. We recommend using Ubuntu Desktop, but Raspberry Pi OS will also run on an Ubuntu Server install. Ubuntu Studio would also be a fine choice. 
 
-To get the best possible audio latency, you should run your Ubuntu computer headless. GPU activity interferes with low-latency audio. Drawing to the screen (or even moving the mouse) can cause audio underruns. This does not mean that you cannot use a desktop install; but it does mean that you should not be using the desktop when using PiPedal. Use a browser on a remote machine, or use a phone or tablet to control PiPedal. It is not entirely clear why GPUs don't play well with realtime low-latency audio. It's probably not caused by interrupts, but may be caused by contention for system memory and various system buses. If you are running a very powerful PC with a GPU that doesn't share system memory, you may be able to run a desktop while using PiPedal; but if you are not getting the latency you think you should, try going back to headless operation. 
-
-Headless, in this context means: nothing is using the GPU. On a Raspberry Pi, it is sufficient to just disconnect the HDMI cables, and not be using a remote desktop connection. It is unknown whether Ubuntu will stop using the GPU if there is an active desktop that is (for example) updating status indicators on the status bar. If in doubt, try disabling automatic login. The system will then stop at the login screen, which does not do any drawing until you start typing credentials. Configuring your Ubuntu desktop to use a text-mode interface instead of a graphical interface would, of course, be perfect; but it seems unnecessarily inconvenient. On an Ubuntu server install, there is no graphical desktop, so this is not a problem. But see the following section about configuring Ubuntu Server before you choose a Server install of Ubuntu.
-
-You might want to consider purchasing a tiny N95, N100 or N150 micro-pc on which to run PiPedal. They are cheap, provide plenty of CPU power, and are exactly the sort of hardware you need to run PiPedal on at a gig, or away from home where you don't have access to a wi-fi network, or a monitor, or a keyboard. N100-series micro-pcs are in many ways preferrable to a Raspberry Pi 5. They provide significantly more compute power, and cost only slightly more.
-
-## Selecting a real-time-kernel kernel on Ubuntu 24.x 
+## Configuring a preempt=full Kernel on Ubuntu 24.x 
 
 By default, Ubuntu installs a PREEMT_DYNAMIC kernel, configured to run with volutary preemption. PREEMPT_DYNAMIC/preempt=voluntary kernels are not capable of supporting real-time audio. To run low-latency realtime audio on Ubuntu, you must reconfigure Ubuntu to use a PREEMPT_DYNAMIC/preempt=full kernel. The PiPedal installer includes a convenient command-line utility that allows you to make the change without having to do painful editing of intimidating system files. Although this is a relatively harmless change, it seemed inappropriate to reconfigure the kernel in the Pipedal package installer. Run the following command-line command after you have installed PiPedal:
 
@@ -43,3 +39,14 @@ To reconfigure Ubuntu Server to use the Network Manager network stack (and there
     sudo apt install network-manager
 
 PiPedal runs perfectly well with the netplan network stack; but the auto-hotspot will be disabled (and actually won't even show up in the UI).
+
+## Running Headless
+
+To get the best possible audio latency, you should run your Ubuntu computer headless. GPU activity interferes with low-latency audio. Drawing to the screen (or even moving the mouse) can cause audio underruns. This does not mean that you cannot use a desktop install; but it does mean that you should not be using the desktop when using PiPedal. Use a browser on a remote machine, or use a phone or tablet to control PiPedal. 
+
+It is not entirely clear why GPUs don't play well with realtime low-latency audio. It's probably not caused by interrupts, but may be caused by contention for system memory and various system buses. If you are running a very powerful PC with a GPU that doesn't share system memory, you may be able to run a desktop while using PiPedal; but if you are not getting the latency you think you should, try going back to headless operation. 
+
+Headless, in this context means: nothing is using the GPU. On a Raspberry Pi, it is sufficient to just disconnect the HDMI cables, and not be using a remote desktop connection. It is uncertain whether Ubuntu will stop using the GPU if there is an active desktop that is (for example) updating status indicators on the status bar. If in doubt, try disabling automatic login. The system will then stop at the login screen, which does not do any drawing until you start typing credentials. Configuring your Ubuntu desktop to use a text-mode interface instead of a graphical interface would, of course, be perfect; but it seems unnecessarily inconvenient. On an Ubuntu server install, there is no graphical desktop, so this is not a problem. But see the section above about configuring Ubuntu Server before you choose a Server install of Ubuntu Desktop.
+
+You might want to consider purchasing a tiny N95, N100 or N150 micro-pc on which to run PiPedal. They are cheap, provide plenty of CPU power, and are exactly the sort of hardware you need to run PiPedal on at a gig, or away from home where you don't have access to a wi-fi network, or a monitor, or a keyboard. N100-series micro-pcs are in many ways preferrable to a Raspberry Pi 5. They provide significantly more compute power, and cost only slightly more.
+