Lua-libmodbus on TRB145

Networking Solutions
1

Dear Community,

I would like to call modbus directly via separate service, because I need to force heating up a humidity sensor in case of high humidity to dry it. When heater is on, of course it is not advised to read temperature, so I must disable this reading, which I can’t achive by webUI.

When I create a simple demo-rtu Lua script with lua-libmodbus like

local dev = mb.new_rtu(“/dev/rs485”, 9600, “none”, 8, 1)
dev:set_debug()
ok, err = dev:connect()
if not ok then error("Couldn’t connect: " .. err) end

but I get error

Opening /dev/rs485 at 9600 bauds (N, 8, 1)
lua: /usr/local/bin/s.lua:200: Couldn’t connect: No such file or directory`

@AndzejJ @anon65719490 I see that you can provide expert knowledge on this topic.

Any clue what’s wrong, why I can’t connect to rs485 ?
I have asked AI regarding to acces to openwrt resources (like user/groups rights) and disabled modbus service to be sure that device is not blocked, but nothing helped.

Regards,
Michal

3

Hello Michail,

Thank you for your inquiry. Your request is currently under review and analysis. Once the evaluation is complete, I will get back to you with further information, findings, or suggestions.

Thank you for your patience in the meantime.

Best regards,

4

Hello,

Apologies for the delay.

Could you please clarify what the intended goal of this Lua script is and elaborate on the script a bit more? As this inquiry is outside of my scope, and I’m not that familiar with Lua scripting, I can only provide you with insights/suggestions to check or try. From the code, I assume you are trying to open an RTU connection on /dev/rs485. Can you confirm if the device /dev/rs485 is actually present and visible under /dev?

Additionally, instead of using a custom Lua script, you can also call the Modbus service directly using ubus commands. For example (change parameters according to your requirements):

ubus call modbus_client.rpc serial.test '{"id":1,"timeout":1,"function":4,"first_reg":2,"reg_count":"2","data_type":"16bit_int_hi_first","no_brackets":1,"serial_type":"/dev/rs485","baudrate":19200,"databits":8,"stopbits":1,"parity":"none","flowcontrol":"none"}'

More useful information and examples for Modbus calls via ubus can be found in related forum topics here:

Best regards,

5

Hi @anon65719490,

Yes, rs485 is present and visible under ls -l /dev so it should be accessible.

lrwxrwxrwx    1 root     dialout         11 Jan  1  1970 rs485 -> /dev/ttyHS0

to use a ubus calls to Modbus Client I need to enable Modbus in WebUI (can be without any calls), with just a lua script I could ‘skip’ WebUI at all and use direct calls to lua-libmodbus.

Regards
Michal

6

Hello @MichalPankau,

Just to confirm, have you already tried using /dev/ttyHS0 directly? From what you’ve shared, I see that the rs485 interface is attached to this particular device node.

Best regards,

7

@anon65719490,

I used an example from github demo-rtu.lua with minor mods, but /dev/rs485 nor /dev/ttyHS0 works.

root@TRB145:~# lua demo-rtu.lua
using libmodbus runtime version:        3.1.6
using lua-libmodbus compiled against libmodbus:         3.1.6
byte timeout:   0       500000
response timeout:        0       500000
Opening /dev/rs485 at 9600 bauds (N, 8, 1)
lua: demo-rtu.lua:14: Couldn't connect: No such file or directory
stack traceback:
        [C]: in function 'error'
        demo-rtu.lua:14: in main chunk
        [C]: ?

root@TRB145:~# lua demo-rtu.lua
using libmodbus runtime version:        3.1.6
using lua-libmodbus compiled against libmodbus:         3.1.6
byte timeout:   0       500000
response timeout:        0       500000
Opening /dev/ttyHS0 at 9600 bauds (N, 8, 1)
lua: demo-rtu.lua:14: Couldn't connect: No such file or directory
stack traceback:
        [C]: in function 'error'
        demo-rtu.lua:14: in main chunk
        [C]: ?

Regards,
Michal

Ubus modbus serial command on RUT956
8

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