RUT956 Modbus not working do_page_fault()

[MarkCobra]

Device: RUT956
Firmware version: RUT9M_R_00.07.07.1
Kernel version: 5.15.149

I am trying to read a register from a power meter using the Modbus Serial Client. When I press test under Request Configuration testing, I get the error: “Failed to test request, check your configuration.”

When I execute the following command in the CLI, I am logged out of the router and see the login page:

ubus call modbus_client serial.test '{"id":1,"timeout":30,"function":3,"first_reg":23297,"reg_count":"1","data_type":"32bit_uint1234","no_brackets":1,"serial_type":"/dev/rs485","baudrate":9600,"databits":8,"stopbits":1,"parity":"even","flowctrl":"none"}'

The Kernel log indicates the following:

Fri May 24 13:34:41 2024 kern.info kernel: [  589.215108] do_page_fault(): sending SIGSEGV to rpcd for invalid read access from 00000000
Fri May 24 13:34:41 2024 kern.info kernel: [  589.223611] epc = 77de5a50 in libc.so[77d65000+aa000]
Fri May 24 13:34:41 2024 kern.info kernel: [  589.228846] ra  = 77bd7d75 in modbus_client.so[77bd2000+1f000]

How do I get modbus to work?
Is this a firmware issue?

[MarkCobra]

Can we see modbus logs with the CLI?

[Marijus]

Hello,

I regret to inform you that Modbus logs cannot be accessed directly through logread. However, we can still attempt to address this issue. Firstly, let’s determine if Modbus is operational on your device, as you have expressed doubts. To do this, we can try reading RUT95 Modbus registers containing device information to monitor our RUT956:

1. Go to Services → Modbus → Modbus TCP Server and enable the server, then save the settings.

2. Next, navigate to Services → Modbus → Modbus TCP Client and configure the settings for testing by reading Modbus registers.

3. After configuring, test the settings below, and you should start seeing system uptime indicators.

Please report back with your findings.

Best regards,

[MarkCobra]

@Marijus thank you for your reply!
I followed your instructions, and this is working fine. How can we further test the Modbus Serial Client?

[Marijus]

Hello,

Firstly, I suggest testing it again with the Modbus Serial Client on RUT956 and double-checking all the settings. Additionally, ensure that the Modbus slave (power meter) is correctly configured and the Modbus instance is running.

Best regards,

[MarkCobra]

@Marijus I think that the settings are correct because they worked on a different Modbus gateway (not from Teltonika). However, I find it strange that I receive an immediate ‘Failed to test request, check your configuration’ error when I click the Test button.

[MarkCobra]

@Marijus Do you have any suggestions for what I should try next?

[MarkCobra]

Is there something I can try to test the Modbus Serial Client?

[Marijus]

Hello,

Sorry for the late reply. Yes, you can test the Modbus serial client the same way I explained for the Modbus TCP client.

You’ll need to connect and enabled Modbus serial server to your Teltonika router. The procedure for testing it is documented in the .gif below. If you have any additional questions, feel free to ask.

Best regards,