Project Modbus + LVGL, strange behaviour

Projects General Guidance
1

Hello

I’m developing a driver and application running on ESP32-P4, that connects to an equipment over Modbus. Therefor I’m using the library “ModbusMaster” (doesn’t seem maintained anymore) and LVGL for the GUI part which is already developed.

I don’t have the Modbus equipment yet. Which isn’t a problem because I also have to take into account the use case where the communication fails.

I’m using this task/LVGL timer to refresh the GUI:

lv_timer_t * task1 = lv_timer_create(rexModulesUpdate, 20000, NULL);

Now the problem:

With this refresh task (which try to connects to the modbus equipment), the GUI is not usable, the display framerate drops to 0 (CPU load is 0 too), and the touch screen doesn’t respond or only after a long time.

Even if a reduce the timeout of the serial port to 20ms (because as said, there is no equipment connected yet), there is no changes.

Now the question:

1. Is this related to the single thread nature of Arduino? In other words I’m stuck.

2. Is it the Modbus library’s fault?

Thank you

2

You seem concerned by the fact the library is untouched for 9 yrs. Have you looked at the ArduinoModBus library by Arduino. It is documented in the Arduino Library section
https://docs.arduino.cc/libraries/arduinomodbus/

3

Well, I read that ArduinoModbus wasn’t compatible with the ESP32s, so I choose a different lib :-/

4

That is an excellent reason.

5

Try replacing rexModulesUpdate with an empty function. I suspect that the problem is that LVGL wants a fast refresh and you’re causing it to block for too long. I vaguely remember running into a similar issue but I can’t think of the specifics right now

6

Yes it’s the problem indeed.

The Modbus is running on the same thread as the GUI, that’s why.

Now the question is if there is a Modbus driver out there that behaves better :confused:

EDIT:

Well there may be a workaround for this problem. I may check if the Modbus connection has timedout, if so, I stop sending new requests for a certain time. It’s at the driver level I think.

7

Is there any reason you can’t run Modbus on a different thread

8

Two reasons:

  1. Arduino doesn’t support multi-threading (I think)
  2. My knowledge :sweat_smile:

I’m gonna pause for some time the fetching of data over Modbus if there is a timeout. It will periodically cause some lag of the GUI, but should be ok.

9

If you’re running on an ESP32 with the arduino IDE, it’s running FreeRTOS under the hood. Just start a new task to manage your Modbus communication.

void rexModulesUpdate(void *pvParameter); ... xTaskCreate(&rexModulesUpdate, "rexModulesUpdate", 2048, NULL, 1, NULL);
1 Like
10

Hey, it works! :face_with_crossed_out_eyes:

Many thanks :slight_smile:

11

Now I’m getting resets of the MCU after some seconds of running :confused:

E (31125) task_wdt: Task watchdog got triggered. The following tasks/users did not reset the watchdog in time:
E (31125) task_wdt: - IDLE0 (CPU 0)
E (31125) task_wdt: Tasks currently running:
E (31125) task_wdt: CPU 0: rexModulesUpdat
E (31125) task_wdt: CPU 1: loopTask
E (31125) task_wdt: Aborting.
E (31125) task_wdt: Print CPU 0 (current core) registers

Do I have to use semaphores, mutex and co in my code?

It’s beyond my knowledge :confused:

12

Something in your modbus code is blocking for too long and causing the watchdog to time out.

13

I have placed a yield() in my driver task and it seems to work… for now :face_exhaling: