Excellent! thank you very much @dissent1, to conclude - all I need to do is connect to UART using USB to UART, connect USB stick with the compiled files and with serial access program, putty for example I can start typing the commands.
Some other questions:
Is there any special soldering need to be made (shorcut) to get UART configuration?
I find in google the following pads layout, please correct me if I'm wrong: PAD 1(next to dot): CS, 2:MISO, 3: WP, 4:GND, 5:MOSI, 6:SCK, 7:HOLD, 8:VCC.
Is there any limitation on the UART to USB cable? or do I need USB to UART TTL cable? I do have a very cheap "CH340T CH340G USB to ESP8266 Serial Wifi Module Development Board Adapter", which I bought in the past for ESP8266 development, is it expected to work?
Yes, when the router has booted completely.
As for your other questions considering uart soldering - I have no clue, I've found a guy that had uart attached already. My unit is still on its way from China
Thanks @dissent1, I got confused because of the Chinese translation for the spiflash pads and understand my mistake now.
There is a UART connector (J4) on the top of the image (see image below) next to the MI logo:
It has 4 pins, I assume pin #1 (left) is for VCC, pins #2-4 are labeled as RX, GND and TX respectively.
Regarding the u-boot interrupt, I understand UART is not enabled by default, so I'm not sure I understand where do I type the commands (which you shared) or how to interrupt u-boot in order to enable UART and type these commands
setenv uart_en 1
Could you please share some clarification on this ?
Please choose the operation:
1: Load system code to SDRAM via TFTP.
2: Load system code then write to Flash via TFTP.
3: Boot system code via Flash (default).
4: Entr boot command line interface.
7: Load Boot Loader code then write to Flash via Serial.
9: Load Boot Loader code then write to Flash via TFTP.