UEFI Instructions: Connect debug UART to PC help


I was following along the instructions, and I got to the point where I had to flash binaries to eMMC. The instructions say to connect the debug UART to a PC. How do I do this? From what I can see, the debug UART is just 4 holes, how am I supposed to connect this to my PC?

Thanks in advance!


If you solder the missing pins [1] you could route the four wires to a serial-USB connector - an example is this one [0].

Then plug the connector to one of the usb host ports of your computer (it should appear as a ttyUSBx).

On a linux hosts system you will probably want to modify /etc/udev/rules/99-usb.serial.rules as follows so that when udev detects the devices it creates a simlik (in the example below it would create /dev/96-hikey)

[jramirez@calypso ~]$ cat /etc/udev/rules.d/99-usb-serial.rules
SUBSYSTEM==“tty”, ATTRS{idVendor}==“0403”, ATTRS{idProduct}==“6001”, ATTRS{serial}==“FTXODWVO”, SYMLINK+=“96-hikey”

Then add a minicom configuration file to your home directory
[jramirez@calypso ~]$ cat .minirc.96-hikey

Machine-generated file - use setup menu in minicom to change parameters.

pu port /dev/96-hikey
pu parity L
pu rtscts No

You would start your console as below without having to worry about the device id.

$ minicom 96-hikey

note: if using UEFI, the console might be routed to the LS expansion (UART2 or UART3).

[0] 0403:6001 Future Technology Devices International, Ltd FT232 USB-Serial (UART) IC
[1] file:///home/jramirez/Downloads/HiKey_User_Guide_Rev0.2%20(1).pdf


If you check the 96 Boards specification (CE spec available from [1]) it says the following with respect to the UART:


One standard UART from the SoC shall​be made available for general purpose use on the low
speed expansion connector.
A second UART (TxD/RxD only) may​be made available on the low speed expansion

Note: Off the shelf FTDI 1.8V serial USB cables may be used to interface to these interfaces

[1] https://www.96boards.org/


Actually, if your are going to use UEFI, then you dont need to solder any pins.
If you look at the grub.cfg [1] file embedded in the boot.img, you can see that it uses AMA3 which is accessible from the LS expansion connector