Dear khong,
Here is a sample for RGMII AT test, include the code and the executable file(Linux X64), if you use other platform you need to recompile
RGMII_AT_Client.zip (5.8 KB)
You need send command AT+QETH="rgmii","enable",0 to enable the RGMII before you send at+qeth=“eth_at”. After that you must reboot your device. You can use ping 192.168.225.1 to test the conection, if you can reach this ip address it proves that the connection is fine.
You can test AT command with this sample, just like ./RGMII_AT_Client + AT command
Hope it helps you，thanks