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Learn how to effectively manage SPI communication using STM32 with HAL. Discover solutions for reading multiple registers and enhancing your code.
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This video is based on the question https://stackoverflow.com/q/67922914/ asked by the user 'Anis AIT' ( https://stackoverflow.com/u/15116973/ ) and on the answer https://stackoverflow.com/a/67936545/ provided by the user 'kkrambo' ( https://stackoverflow.com/u/1401213/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Mastering STM32 SPI Communication with HAL

In the realm of embedded systems, efficiently managing data transfer is crucial. One of the popular protocols for achieving this is Serial Peripheral Interface (SPI). However, when newcomers attempt to use SPI for communication, especially with devices like gyroscopes, they might encounter challenges. Recently, a developer faced issues while implementing SPI communication on an STM32 microcontroller with the HAL library. Let’s dive into the problem and explore a robust solution.

The Challenge

The developer generated code using CubeMX for SPI communication with a gyroscope (L3GD20). While they successfully read the WHO_AM_I and CTRL_REG1 registers individually, difficulties arose when attempting to read both registers sequentially. The HAL_SPI_Receive command kept returning the same value from the first HAL_SPI_Transmit, indicating a fundamental communication issue. The developer sought guidance on using the HAL_SPI_TransmitReceive function for reading bytes from different registers effectively.

Analyzing the Code

Here’s a snippet from the developer's implementation that highlights the issue:

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

Observations

The first read works fine, but subsequent reads produce consistent results, indicating a possible issue with how data is transmitted and received.

The artificial delay before the second read may not adequately prepare the communication bus.

The method of transmitting and receiving data separately is less efficient.

The Effective Solution: HAL_SPI_TransmitReceive()

To resolve the issues experienced, it's recommended to use the HAL_SPI_TransmitReceive() function. This method simplifies reading from multiple registers by handling the transmission and reception in a single call.

Example Implementation

Here’s how you can implement this in your code:

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

Explanation of the Solution

Addressing the Register: The first byte of tx_data contains the register address with the read command bit set (indicated by | 0x80).

Dummy Byte: The second byte is a dummy byte, necessary because the SPI protocol allows both master and slave devices to send and receive data simultaneously during each byte transmission.

Combined Command: The call to HAL_SPI_TransmitReceive() sends both the address and the dummy byte, manages the clock signals, and receives the response on the second byte.

Accessing the Result: The data you want (the actual register value) is found in the second position of rx_data.

Conclusion

Navigating SPI communication with STM32 and HAL can seem daunting at first, particularly when reading data from multiple registers. However, by utilizing the HAL_SPI_TransmitReceive() function, you can streamline the process and achieve more reliable results. This approach not only resolves issues related to multiple read operations but also enhances the clarity and efficiency of your code.

With these insights, you will be well on your way to mastering SPI communication with STM32 microcontrollers. Happy coding!