Receiving UART data from a UART port different than the Modbus port causes Modbus to stop working

[emptor8]

Hi there,

Thanks for this great library! I'm seeing the following problem:

• If I only use the Modbus library on UART port 1, everything works well.

• If I enable UART port 2 to output messages via HAL_UART_Transmit(&huart2, data, size, timeout), Modbus on UART port 1 still works fine.

• However, once I try to receive input on UART port 2 (e.g. via HAL_UART_Receive(&huart2, data, size, timeout), Modbus on UART port 1 no longer works.

Do you know what I'm missing here?

Note: I added conditional checks in UARTCallback.c to only run the code logic in the callbacks for the &huart1 instance. If the &huart2 instance is detected, the callbacks do nothing.

[alejoseb]

Hi, If you have a complete example to reproduce your issue I can take a look. There could be multiple reasons for this issue. For example, If the task where you are reading from serial has higher priority than the modbus task and you are using a blocking operation, like the function in your comment, then is possible that the modbus task is not being executed by the FreeRTOS scheduler. It should be better if you use a non-blocking reading method, and a notification from the callback to the task when data has arrived.

[emptor8]

Attached is a complete example that demonstrates the issue I'm having.

• debugTask1 waits for input from the keyboard via HAL_UART_Receive() on huart5
• debugTask2 toggles an LED on the NUCLEO board
• Modbus slave task is running and using huart4

Things work fine if I comment out HAL_UART_Receive() -- I can still transmit UART data on huart5 and run the Modbus on huart4 at the same time.

However, with HAL_UART_Receive() on huart5, it prevents Modbus from running on huart4. The LED is still being toggled in debugTask2 though, so it seems like the CPU isn't being held up by HAL_UART_Receive()? I've also made debugTask1 and debugTask2 lower priority than the Modbus slave task but this does not help.

modbus_test_12.22.21_v1.zip

[emptor8]

Hey @alejoseb, did you get a chance to reproduce this?

[alejoseb]

I cannot reproduce your issue since I don't have your board, and you did not include the modified version of the modbus library in the zip it is only a link. I quickly checked the code though. I saw that you use portMAX_DELAY for waiting for a character, that is wrong. portMAX_DELAY is a freertos macro, it is not meant to work with the HAL library, I don't know what could be the effect of using that macro. Besides, you should use interrupt mode to receive the character no the blocking mode. The blocking mode does not yield. Another option could be to use the blocking mode but with a few ms timeout and check the returned value of the HAL function. HAL_OK should mean that you received a character.

I am closing this issue since it is not related to the library.