How to update the Freeplay from Compute module 3 to Compute module 3+

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I'm sorry about the slow response.  It is often difficult for us to reply during the weekend.

You should be able to get your old SD image up and running on the new compute module, but it can be a little tricky.   I would definitely recommend making a backup of the SD card before you proceed.  

Make sure that the Compute Module 3+ is a "LITE" version.

NOTE that there is a fair chance that this update will "break" the button driver, and you'll need to reinstall it.  That's not difficult, but you'll need so SSH in (or maybe use a USB keyboard) to fix that after the reboot.

Insert the original Compute Module 3.
Connect your Freeplay CM3 to the internet.

IF you want to, you may be able to skip the first part if you prefer not to upgrade as much stuff.  I'm not 100% sure if it'll work (depending on the current state of your operating system), but you could try it.  The script that fixes the button/joystick driver may also update your kernel.

=== FIRST PART / Updating Operating System and Packages ===
Boot up to the main menu.
Select "RetroPie"
Select "RetroPie Setup"
Select "Update"
At "Update Installed Packages" select "Yes"
At "Update the underlying OS packages" select "Yes"
WAIT
Select "Perform Reboot"
=== ===

=== FIX JOYSTICK/BUTTON DRIVER ===
Turn the machine back on.
SSH into the machine (OR connect a keyboard and then hit F4 to get to the command prompt) and type the following
cd /home/pi/Freeplay/mk_arcade_joystick_rpi/
./install.sh
sudo shutdown -h now
=== ===

NOTE!!!  If the fix joystick button driver process got a new kernel, it would likely work on the CM3+, but it would also likely need to be re-run, so do the "=== FIX JOYSTICK/BUTTON DRIVER ===" a second time if the buttons still don't work after rebooting.  I ran through this entire process while writing this response, and I had to do the joystick driver install twice.  The first time it downloaded/installed a bunch of stuff.  The second time installed the new driver.