Where to start with this device (SDX55)?

What is the default password for the Openwrt 15.05.1 management page? Also how should root access be obtained?

Are you using this device?

The default password is blank, with username root.

Simply by logging in. If you cannot login, it is because the device is using a customized fork and you’ll likely need to contact the vendor.

Also keep in mind that 15.05 is truly ancient and is completely unsupported now.

Yes, but I can't use it normally at the moment, it's over~ username root password is empty, I can't log in after trying!

Reread the reply, and understand

I had to make a custom factory-build firmware for this device with the comports enabled
my device does not have open installed, it has more prevalent qualcomm chip with os2

I have usb ttl adapter, get console UART ttl here.

Nice,its 1.8V layer?

Yes, 1.8v

can someone share a firmware dump? accidentally bricked mine trying to make a 23.05.3 port for it