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RP4 - Cannot get bootmessages to UART

Posted: Wed Sep 25, 2019 5:55 pm
by krbvroc1
My goal is to route all kernel boot messages to the UART4. I already have ttyAMA1 configured.

I whittled down my /boot/cmdline.txt to only the following:

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dwc_otg.lpm_enable=0 console=/dev/ttyAMA1,115200 root=PARTUUID=aaaaaaaa-02 rootfstype=ext4 elevator=deadline rootwait
My /boot/config.txt contains:

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dtoverlay=pi3-disable-bt
# Enable UART4 debug console
dtoverlay=uart0
dtoverlay=uart4
With the above, on the connected HDMI display there is no output, but there is also NO output on the UART either! Once the system boots, I have (after reconfiguring the getty to use ttyAMA1) a login prompt on the UART. But there are no boot messages.

Re: RP4 - Cannot get bootmessages to UART

Posted: Thu Sep 26, 2019 10:21 pm
by dgordon42
The 'dtoverlay=pi3-disable-bt" has now been changed to:

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dtoverlay=disable-bt
The 'pi3-disable-bt' remains as an alias, but I don't know if it works on a Pi4.
When using 'dtoverlay=disable-bt', it is also necessary to issue the command

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sudo systemctl disable hciuart
once and reboot, otherwise '/dev/ttyAMA0' is still tied to Bluetooth.
Details in '/boot/overlays/README'

As you are trying to get boot messages on '/dev/ttyAMA1', and Bluetooth normally uses '/dev/ttyAMA0', I'm not sure the above will solve your problem, but worth trying.
As a troubleshooting step, I would try putting the phrase 'console=serial0,115200' back into '/boot/cmdline.txt' and see if you get boot messages on GPIO pins 14 and 15.

Dave.