Linux

I got an Orange Pi 5 Plus to play with smallish AIs (because it has an NPU) and I normally access it remotely, so I have to know its IP address to do it.

In order to easilly know the IP address of it, I've wired a little 128x64 monochrome OLED screen to it (Orange PIs, like Raspberry PIs have a pin connector giving access to GPIO and interfaces like I2C, Serial and SPI) which talks via I2C.

Turns out those interfactes aren't active in Linux by default (I.e. no /dev/i2c-x), so I figured out that I had to add a kernel overlay to activate that specific interface (unlike with the Raspberry PI whose Linux version has a neat program for doing it, in the Orange Pi you have to know how the low level details of activating those things), which I did.

To actually render characters on that screen I went with an ARM Linux port of a graphics library for those screens I used before with Arduino, called u8g2)

Then I made a program in C that just scans all network interfaces and prints their names and IP addresses on that screen, and installed it as a Cron job running once a minute.

Now, as it turns out when you shutdown your Linux on that board, if you don't disconnect it from power there is actually still power flowing through the pin connector to any devices you wire there, so after shutdown my screen would remain ON and showing the last thing I had put there, but because the OS was down it would naturally not get updated.

So the last thing I did was another small C program which just sends to that screen the command for it to go into power saving mode, shutting it down. This program was then installed as a Systemd Service to run when Linux is shutting down.

The result is now that there is a little screen hanging from the box were I put this board with Linux which lists its IP addresses and the info is updated if it connects other interfaces or reconnects and gets a new IP address. Curiously I've actually been using that feature because it's genuinely useful, not just a funny little project.