08-03-2020, 03:44 AM
(08-02-2020, 02:18 PM)ThatGeoGuy Wrote: I've made a terrible mistake and installed the stock debian kernel, and now my system boots to a black screen.
Does anyone know how to pull up the GRUB menu from uboot so I can switch back over to the correct kernel?
U-Boot presents its menu over the serial port. To talk to it, you'll need a 3.3V serial interface that can do 1.5Mbaud, which you can plug it into the PBP's audio port. You'll also need to flip the switch on the PBP's mainboard that enables the serial port.
Note that it's really easy to end up with a 5V serial adapter. The one I bought from the PINE store ended up being 5V, and caused horrible problems when I tried to actually use it. I tried another adapter from a different manufacturer, and it turned out to be 5V as well. (In both cases, the part was advertised as 3.3V.) At that point, I ran out of money to keep trying to find a 3.3V adapter and just... used other means of debugging.
If you don't already have a fast 3.3V serial interface available, and either an adapter or some cable-making experience, you're probably better off making an install of some bootable Linux to an SD card, chrooting into your main system, and removing the stock kernel package. (Assuming you're running from the eMMC.)