I’m doing a little troubleshooting on the Raspbrry Pi 3 B+ and figured I’d add my notes somewhere for safe keeping.
I’ve added a fancy metal momentary push button with blue led surround to switch my Volumio off/on using GPIO 3 and GPIO 4 with the GPIO Buttons plugin and a pair of diodes on the switch to ground both inputs when the switch is depressed.
I am using the UART on GPIO 14 to energize the LED when the Raspberry Pi is running which has used in the past however, apparently the Raspberry Pi 3 B+ uses a software UART rather than hardware and as a result, the LED energizes for a few seconds during boot and then extinguishes.
I’ve done some digging around and there is a fix which causes a kernel panic and there is another fix for that too.
In order to make GPIO 14 to energize the LED when the Raspberry Pi 3 B+ is running, we need to add a line to userconfig.txt in the boot directory to turn the UART on: enable_uart=1
When I added this line, it caused my system to hang on boot and it never came on line. Apparently this is a problem in the Raspberry Pi 3 firmware and in order to correct it we need to do the following. We need to edit the cmdline.txt which is also in the boot directory. We need to remove the reference to kgdboc. In my instance of Volumio, I removed kgdboc=serial0,115200 from the file and it came back online just fine.
If anyone has anything else to add, I’ll be happy to update my system. I have a concern that when I do another update on Volumio, I will need to edit cmdline.txt before I reboot or I run the risk of a broken system.