Raspberry Pis GPIO pins include a serial port and can run at 115200. I've used that for monitoring the boot process as it can be configured to put out messages

Raspberry Pis GPIO pins include a serial port and can run at 115200. I've used that for monitoring the boot process as it can be configured to put out messages before anything goes to the screen. When the boot process halts with nothing on the screen, there may still be useful information put out to the serial port.