jTAG / UART / serial console access for ROCKPro64 with CH340 UART USB

I bought ROCKPro64 quite long time ago and it's still pretty good even in 2024. So I decided to install official Debian for it to use it for NAT64 gateway and home automation platform. 

To install Debian I need console access as HDMI does not work until you install Linux Distro which supports it.

So I decided to play with serial port access. On SBC you need to plug 3 pins to Pi-2-bus with following order.

On CH340 you need to plug them in following order:

And yellow jumper need to be in 3V3 mode this way:

Then you need to plug CH341 to your PC and check that it recognised correctly in dmesg:

[ 6981.858478] usb 1-5: new full-speed USB device number 23 using xhci_hcd

[ 6982.107488] usb 1-5: New USB device found, idVendor=1a86, idProduct=7523, bcdDevice= 2.64

[ 6982.107492] usb 1-5: New USB device strings: Mfr=0, Product=2, SerialNumber=0

[ 6982.107494] usb 1-5: Product: USB Serial

[ 6982.120247] ch341 1-5:1.0: ch341-uart converter detected

[ 6982.134269] usb 1-5: ch341-uart converter now attached to ttyUSB0

It may not connect from first attempt but you can try it multiple times to get required results.  

After that you can run screen or minicom on your Linux box:

screen /dev/ttyUSB0 1500000

And finally reboot SBC using power (keep it for 5+ seconds) or reset button and then you will see boot sequence:

Hit any key to stop autoboot: 1 

switch to partitions #0, OK

Scanningmmc1:1... 

Retrieving file: /extlinux/extlinux.conf

Enter choice: 1:        Debian-Installer

Retrieving file: /initrd.gz

Retrieving file: /dtbs/rockchip/rk3399-rockpro64.dtb

Moving Image from 0x2080000 to 0x2200000, end=4050000

 01f00000

   Booting using the fdt blob at   Loading Ramdisk to ef112000, OK

   Loading Device Tree to 00000000ef0ff000, end 00000000ef111300OK

Starting kernel ...

My guide was based on this reference guide. 

In some cases device may refuse loading when TXD cable is plugged and you will need temporarily unplug it.