Avoid Boot Loops, Try Librem 5 Serial

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David Hamner

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Debugging a Librem 5 that boots is pretty easy–just open a terminal or access the serial console over USB. But if you are doing kernel development or porting alternative OSes to the Librem 5, you might end up with a Librem 5 that won’t boot far enough to load regular diagnostic tools. When that happens it’s time for raw serial access.

How to Enable Raw Serial Access on the Librem 5

If your Librem 5 is fully booted, simply attach it to your computer with a USB-C cable. You’ll be able to connect to it like any standard serial device. On PureOS run:
sudo picocom -b 115200 /dev/ttyACM0You can use a USB serial device like a FTDI/UART cable for a bit lower-level access by soldering on a few wires to your Librem 5. This gives you access to U-Boot as well as early boot messages. You’ll need a soldering iron, solder, a few wires, and a USB serial device to get started.Power down, and remove the back cover and battery.Unscrew the backplate.This will expose the needed pads you’ll need to solder to.Follow this guide to disassemble your Librem 5 further if the frame is too close for comfort.

These are the pads needed for serial communication.Add a small amount of solder to the pad, then add solder to the wire and attach the pad and wire.After attaching all the wires, you can use the backplate to clip down and help prevent the new connections from breaking.You can now attach the UART USB cable to your computer and run this command:

sudo picocom /dev/ttyUSB0 -b 115200With the serial connection setup, you can check console output on a test build even if your build cannot fully boot. Find out more about the Librem 5 or dive into the docs.

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