Implementing ppp_byte_send for NXP MIMXRT1040-EVK with ThreadX

Learn how to effectively implement the `ppp_byte_send` function for PPPoS on NXP's MIMXRT1040-EVK using ThreadX, and resolve common UART communication issues.
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Implementing ppp_byte_send for NXP MIMXRT1040-EVK with ThreadX

When working with embedded systems, achieving a reliable communication protocol between devices can sometimes pose significant challenges. If you're delving into the world of PPPoS (Point-to-Point Protocol over Serial) on NXP's MIMXRT1040-EVK and trying to get it running seamlessly with ThreadX, you may find yourself grappling with the intricacies of the ppp_byte_send function.

In this guide, we will explore a common problem developers face when implementing the ppp_byte_send to send data over UART. By understanding the underlying cause and discovering the correct implementation strategy, we can ensure smooth communication with the modem (in this case, the Quectel EG800Q).

Problem Overview

The challenge at hand involves sending a single byte of data over a serial interface to a modem using the ppp_byte_send function. Originally, the implementation utilized the LPUART_WriteBlocking function from NXP's Software Development Kit (SDK) in a way that didn't yield the expected results:

[[See Video to Reveal this Text or Code Snippet]]

When this code was executed, the modem failed to respond. The lack of response led to confusion and further testing, including attempts to send multiple bytes in a single call or through a looping method—none of which proved successful.

Understanding the Solution

After careful consideration, the root of the problem was identified: the LPUART_WriteBlocking function is designed to take a pointer to the data, rather than a single byte. Here's the revised implementation that rectifies the issue:

[[See Video to Reveal this Text or Code Snippet]]

Breakdown of Changes

Pointer Usage: The primary change is passing the address of the byte variable (using &byte) instead of the byte itself. This ensures that LPUART_WriteBlocking receives the correct pointer to the data.

Confirmation of Functionality: After this adjustment, the function was tested again and confirmed to work as expected. The modem began responding correctly to the byte data sent to it.

Additional Considerations

While this change solved the immediate problem, there are a few more aspects to keep in mind:

Make sure that the UART speed is correctly configured to match the modem's requirements (in this case, set to 115200 bps, which you noted).

Ensure that any additional configurations required by the modem are set properly before sending data.

Conclusion

In developing applications for embedded systems, minor oversights can lead to significant hurdles, particularly in communication protocols. By ensuring you're passing data correctly as pointers, you can avoid many common pitfalls.

With this updated understanding of how to implement ppp_byte_send correctly using ThreadX on the MIMXRT1040-EVK, users can streamline their development process and establish effective communication with their modems.

Happy coding!