USB-UART Module Kit
USB-UART connected to ODROID-C2
Serial console early boot messages
Sometimes we need to vew the early boot messages of the ODROID-C2. This is the case when we are dealing with a problem during boot, or creating a special purpose boot image, or when we add new external devices.
In order to view the early boot messages we need to connect our ODROID-C2’s serial console port to a USB port of another Linux box, using a USB-UART Module Kit (see the pictures above). This allows us to have remote serial access to our ODROID-C2, in a similar manner as an SSH connection would.
However, the serial console is better suited for such debugging scenarios than ether SSH or HDMI and keyboard combination would. That is because the serial console allows us to interact with the ODROID-C2 even when the SSH is not accessible and the HDMI monitor is blank. Such scenarios are:
Diagnostic messages prior to the initialisation of the HDMI interface
Diagnostic messages in case of problematic (or disabled) initialisation of the HDMI interface (e.g. setenv nographics "1" configuration inside boot.ini)
Diagnostic messages prior to a failed boot
When we want to interrupt the automated boot process (hitting [Enter] twice during boot) to start an interactive u-boot shell. U-boot is a boot loader similar to lilo or grub, but is specifically designed for embedded devices like the ODROID-C2. Using the u-boot shell we can interactively test new boot configuration, load new kernel image, boot rootfs from a different partition, fix a failed boot process, and so on (essentially manually entering the boot commands found inside boot.ini).
Follow these steps to connect to ODROID-C2’s serial console:
Connect the USB-UART cable to the serial console port of the ODROID-C2 and the USB port of another Linux box
Power on the ODROID-C2 via the microUSB or the DC connector
Connect to the ODROID-C2 from the Linux box by typing sudo minicom -b 115200 -D /dev/ttyUSB0
For more information refer to Get more out of "Das U Boot" and the section "USB / UART kit" from the HARDKERNEL ODROID-C2 USER MANUAL.