Loss of /dev/ttyUSB2 and /dev/ttyUSB3

Technical Subjects
1

After issuing some AT commands to RM520N-GL, I lost the AT port at /dev/ttyUSB2 and also /dev/ttyUSB3, and I can no longer send it any AT commands.

I have only /dev/ttyUSB0 and /dev/ttyUSB1. The ethernet port of the board also gives 192.168.225.1.

Is there a way to reset RM520N-GL, so I could regain the AT port?

FYI, cat /sys/kernel/debug/usb/devices returns

T: Bus=01 Lev=01 Prnt=01 Port=00 Cnt=01 Dev#= 3 Spd=480 MxCh= 0
D: Ver= 2.10 Cls=00(>ifc ) Sub=00 Prot=00 MxPS=64 #Cfgs= 1
P: Vendor=2c7c ProdID=0801 Rev= 5.04
S: Manufacturer=Quectel
S: Product=RM520N-GL
S: SerialNumber=hidden
C:* #Ifs= 6 Cfg#= 1 Atr=a0 MxPwr=500mA
A: FirstIf#= 0 IfCount= 2 Cls=ef(misc ) Sub=04 Prot=01
I:* If#= 0 Alt= 0 #EPs= 1 Cls=ef(misc ) Sub=04 Prot=01 Driver=rndis_host
E: Ad=81(I) Atr=03(Int.) MxPS= 8 Ivl=32ms
I:* If#= 1 Alt= 0 #EPs= 2 Cls=0a(data ) Sub=00 Prot=00 Driver=rndis_host
E: Ad=8e(I) Atr=02(Bulk) MxPS= 512 Ivl=0ms
E: Ad=0f(O) Atr=02(Bulk) MxPS= 512 Ivl=0ms
I:* If#= 2 Alt= 0 #EPs= 2 Cls=ff(vend.) Sub=ff Prot=30 Driver=option
E: Ad=01(O) Atr=02(Bulk) MxPS= 512 Ivl=0ms
E: Ad=82(I) Atr=02(Bulk) MxPS= 512 Ivl=0ms
I:* If#= 3 Alt= 0 #EPs= 3 Cls=ff(vend.) Sub=00 Prot=40 Driver=option
E: Ad=84(I) Atr=03(Int.) MxPS= 10 Ivl=32ms
E: Ad=83(I) Atr=02(Bulk) MxPS= 512 Ivl=0ms
E: Ad=02(O) Atr=02(Bulk) MxPS= 512 Ivl=0ms
I:* If#= 4 Alt= 0 #EPs= 3 Cls=ff(vend.) Sub=00 Prot=00 Driver=qmi_wwan
E: Ad=86(I) Atr=03(Int.) MxPS= 10 Ivl=32ms
E: Ad=85(I) Atr=02(Bulk) MxPS= 512 Ivl=0ms
E: Ad=03(O) Atr=02(Bulk) MxPS= 512 Ivl=0ms
I:* If#= 5 Alt= 0 #EPs= 3 Cls=ff(vend.) Sub=00 Prot=00 Driver=qmi_wwan
E: Ad=88(I) Atr=03(Int.) MxPS= 10 Ivl=32ms
E: Ad=87(I) Atr=02(Bulk) MxPS= 512 Ivl=0ms
E: Ad=04(O) Atr=02(Bulk) MxPS= 512 Ivl=0ms

2

Can you telnet to 192.168.225.1 port 1555 ?

3

$ telnet 192.168.225.1 1555
Trying 192.168.225.1…
Connected to 192.168.225.1.
Escape character is ‘^]’.

May I ask what to do next?

4

See RM502Q-AE and at+qeth="eth_at" - #2 by Bryan.Tan-Q

5

Thanks. Let me try to understand your instructions.

Are you saying that, since my board response to telnet, I should try to run Bryan.Tan’s code RGMII_AT_Client.zip, which can send AT commands to the board using the RGMII protocol?

6

Yes, I would try that.

7

I managed to download and try the RGMII-AT Client tools without success. Could you tell me what to do next?

Below are the results of RGMII-AT Client.

$ python direct-port.py
RGMII-AT Client Up => 192.168.226.1:1555
Can Not Connect To => 192.168.226.1:1555
Can Not Connect To => 192.168.226.1:1555
Can Not Connect To => 192.168.226.1:1555
(repeat infinitely …)

$ python quectel_rgmii_at_client.py --modem-ip=192.168.225.1 --modem-port=1555 --at-command=ATI
Can Not Connect To => 192.168.225.1:1555
[Errno 56] Socket is already connected
Can Not Connect To => 192.168.225.1:1555
[Errno 56] Socket is already connected
(repeat infinitely …)

Meanwhile, ping 192.168.225.1 is normal, and
$ telnet 192.168.225.1 1555
Trying 192.168.225.1…
Connected to 192.168.225.1.
Escape character is ‘^]’.

8

My understanding that if you do not see ?RGMII_ATC_READY in your telnet connection then your modem is not configured for this type of connection.

I can think of using UART or chase Quectel for a magic command that you could send via Diag interface (ttyUSB0).