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I am using a CP2102 Module to connect my PC with the Pi's GPIO port. Although there are some errors but now I can see some output every time I reboot the Pi.

[   49.739893] systemd-cgroups-agent[177]: Failed to get D-Bus connection: Failed to connect to socket /org/freedesktop/systemd1/private: Connection refused
[   49.757494] systemd-cgroups-agent[178]: Failed to get D-Bus connection: Failed to connect to socket /org/freedesktop/systemd1/private: Connection refused
[   50.958737] Restarting system.

I believe this means the physical connection and the hardware works OK. However, unlike what this article descripted, there are no boot up messages, nor can I access the console login.

The Pi is running ArchlinuxARM, what can I do to activate the serial console?

UPDATE

(Content moved to the answer.)

Earth Engine
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1 Answers1

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Following some suggestions in the comment, ps aux | grep getty shows no ttyAMA0 instances so the serial console is not started. Following the official Archlinux guide for Raspberry Pi, I enabled the console:

systemctl start getty@ttyAMA0
systemctl enable getty@ttyAMA0.service
ln -s /usr/lib/systemd/system/getty@.service /etc/systemd/system/getty.target.wants/getty@ttyAMA0.service

I can now connect to the serial console. By editing the cmdline.txt as the following, the kernel message shows up as well:

loglevel=5,console=ttyAMA0,38400 kgdboc=ttyAMA0,38400 (...other options)

FURTHER TIPS

If the Pi is powered by the PC through a USB cable, since they share the same ground, only TxD and RxD need to be connected. If the Pi is using another power source, Connect the Ground cable as well otherwise the console will keep receiving rubbish data.

Earth Engine
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