As Goose requested it I'll post a fwp build for the 4100/5100... It's basically the official tvix_M-x100_1.3.15.fwp with telnetd, sshd (nonworking), httpd (start via telnet), and ntpdate (run via telnet).
Warning. This works for me, but don't hold me responsible for anything. This release should be considered experimental and should not be used by anyone who is not comfortable with possibly bricking their box. Before any upgrade, make sure you have the possibility to unbrick your unit.
Download tvix_M-x100_1.3.15_POC.zip
I recommend you to make your own build instead of downloading this. That way you'll learn something, and get ready to contribute to the community. We are ready to help you if something is unclear on how to do it.
