Add Radxa E20C board

[mattx433]

Description

Adds the Radxa E20C board, which is based on the Rockchip RK3528 SoC.
U-Boot config from radxa/u-boot@5202c42
Depends on armbian/linux-rockchip#231 (which, as of writing, is not merged) (which is now merged)

How Has This Been Tested?

• Boots (from microSD)
• USB serial via debug port works (see note)
• LAN port works (RK3528 Ethernet)
• WAN port works (RTL8168 Ethernet)
• Debug USB-C port works (can run USB gadgets)
• USB-A port works (can use USB devices)
• User button works (via /dev/input/event0)
• LED control works (via /sys/class/leds)
• eMMC access works

Not tested:

• RKMPP (did not find any tools that worked with the 6.1 kernel, only 5.10)
• eMMC boot (should work, though flashing tools are unreliable)

Note that USB serial is unreliable, likely due to the CH340B USB serial chip on the board not being able to handle the RK3528's baudrate. Changing the baudrate can only be done by editing the device tree (as stty will not affect it).

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• My changes generate no new warnings
• Any dependent changes have been merged and published in downstream modules

[EvilOlaf]

The CH430B can handle up to 2Mbaud AFAIK so maybe there is some different issue. Could also be due to poor design which would not be fixable by software anyway.

[RadxaStephen]

Note that USB serial is unreliable, likely due to the CH340B USB serial chip on the board not being able to handle the RK3528's baudrate. Changing the baudrate can only be done by editing the device tree (as stty will not affect it).

We have noticed that when the OS sets the debug serial port baud rate to 1.5M, the serial port tool will lose characters. When setting baud rate to 115200, the serial port will not lose characters.

We found that it is a problem with CH340B itself.

To solve this problem, we need to use another Pin to Pin IC, CH340C.
We will release a new Radxa E20C with CH340C.

[overrunner]

Nice work! Is there a how to for installing Armbian on the E20C available?

[igorpecovnik]

Is there a how to for installing Armbian on the E20C available?

This is always the same.
https://docs.armbian.com/User-Guide_Getting-Started/

... but you will need:

• wait for automation to generate image https://github.com/armbian/community
• build on your own https://github.com/armbian/build/blob/main/README.md