10MB Full Duplex is strange to me 
When I was trying to unbrick mine I was getting eth0 PHY2 up Speed :1000 Full duplex...
If the setting for "Speed and Duplex" keep in dafault "Auto Negotation" the link goes down quickly and I can't see the DHCP Discover outgoing packets from the router.
The only progress I got was that, changing that advanced setting on windows PC to 10MB. Al least, I can see DHCP Discover requests.
Personaly when plugged from LAN of AX6 to my computer with no special settings I don't remember receiving DHCP requests the only thing I got was that
eth0 PHY2 up Speed :1000 Full duplex
In the serial output and that was enought to trigger the MiWifiRepairTool.
Check your tftp.log in MiWifiRepair folder and you will see the DHCP protocol trace before TFTP transfer.
Something is different in this case and I don't know what could be. I tried all of the success procedures that I saw in this and other forums without success.
The only line I was getting was complex DNS request: ignored. I din't have the file anymore (I was using my sister's computer which is now +100km away) + I think you'll understand that I on't really want to reset my router again ^^
People, I have a question: If the serial input is disabled, ¿How is possible rebooting the U-boot TFTP recovery with the keystroke "Ctrl+c" ??
Its not disabled, just ignored by U-boot
The same happens to me.. I'm unable to transfer the image to the router
the problem started when I had openwrt and I lost 2,4 and 5 Ghz interfaces (ath11k) only the iot remains..
I tried to install the original firmware and it reboots every time:
Coundn't get reading for the sensor x is 0x0020***** an reboots at 5 seconds... a full bootloop and at the same i can't use tftp... I'm completely lost!
Up I think is a hardware problem
Can someone one help me please!
Im trying to unbrick my device with serial port but i cant stop autoboot!
Is anything i can do?
Can you confirm that you can reset the tftp recovery process with "ctrl+c" keystroke?
No i can't reet u-boot . I can't type nothing with keystroke!
My ax3600 is garbage now!
If UART TX was not enabled then you can only see the output and not write anything
It's strange because I've enabled before!
Boot waiting is still on!
PCI1 is not defined in the device tree
In: serial@78B3000
Out: serial@78B3000
Err: serial@78B3000
machid: 8010010
MMC Device 0 not found
eth5 MAC Address from ART is not valid
write phy_id=1, reg(0x8074):0x0670
write phy_id=2, reg(0x8074):0x0670
write phy_id=3, reg(0x8074):0x0670
write phy_id=4, reg(0x8074):0x0670
bootwait is on, bootdelay=5
Then its rather weird
Even with UART disabled, CTRL+c should reset the tftp recovery proccess during BOOTP broadcast 1, BOOTP broadcast 2, etc. This is in order to discard some problem with ttl-usb adapter and wires connections.
So do you think i have any issues with my usb uart?
No, I do not know. But this way we can confirm it is ok.
Is any option to confirm if Rx is well connected.
I mean if is not well soldering or any other miss connection between tx uart to rx router if uart is disabled?
That is exactly what I said you to try...
Start the tftp recovery in the router (boot with reset button pressed) and without a TFTP server(or Xiaomi recovery tool) connected to the router.
During the BOOTP broadcast series if you hit "ctrl + c" keystroke the router receive the interrupt and reset the BOOTP broadcast as you can see in the picture I posted.