MIMXRT1180-EVK LPSPI Troubleshooting: A Zephyr RTOS Deep Dive

by Sebastian Müller 62 views

Hey everyone, it looks like we've got a bit of a puzzle on our hands today. We're going to dive deep into a fascinating issue reported on the Zephyr Project RTOS with the NXP MIMXRT1180-EVK board, specifically concerning the LPSPI (Low Power Serial Peripheral Interface) functionality. If you're wrestling with similar problems or just curious about embedded systems debugging, you're in the right place. Let's get started!

The Curious Case of the Malfunctioning LPSPI

Our main focus today is on LPSPI problems encountered on the NXP MIMXRT1180-EVK board, particularly when trying to communicate with an ADC (Analog-to-Digital Converter). The core issue seems to stem from the NXP's LPSPI driver itself, with specific hiccups occurring in the MOSI (Master Output Slave Input) and MISO (Master Input Slave Output) lines. Interestingly, the clock signal appears to be functioning as expected, ticking away at the configured 4MHz, which indicates the clock setup is likely correct. However, the data transmission? That's where things get a little wonky. Let's break this down further.

Decoding the MOSI and MISO Mystery

To kick things off, the initialization of the AD7194 ADC driver involves sending a series of five 0xFF bytes via SPI using the spi_write_dt function. Now, here's where it gets interesting. A logic analyzer, our trusty tool for peeking into the electrical signals, reveals that the MOSI and MISO lines aren't behaving as expected. Instead of seeing a continuous high signal (which represents 0xFF) on the MOSI line, the signal appears distorted or incorrect. It’s like trying to send a clear message but the words are getting garbled along the way. This discrepancy immediately suggests that there's a miscommunication happening at the hardware level. The data we intend to send isn't what's actually being transmitted. This is a classic symptom of a lower-level driver or hardware configuration issue, and it’s a critical point in our investigation.

Diving into Debug Logs: A Peek Behind the Curtain

To shed more light on this issue, our intrepid investigator enabled CONFIG_SPI_LOG_LEVEL_DBG, a debug setting that provides verbose logging information. This is akin to turning on all the lights in a room to see what's really going on. After a system reset, the driver attempts to read the ADC's ID. During this process, something peculiar was observed in the spi_context_buffers_setup function: the buffers appeared to be non-empty. This is quite unusual because, in a properly functioning system, these buffers should be clear before a new SPI transaction begins. The presence of data in these buffers suggests that either the previous SPI operation didn't complete correctly or there's a data management issue within the driver. It's like finding leftover ingredients in the kitchen before you even start cooking—something isn't quite right with the process.

The FRDM-K64F Reference Check: A Tale of Two Boards

To ensure that the problem wasn't specific to the sensor itself, a clever comparison was made using the FRDM-K64F development board as a reference. This is a fantastic troubleshooting step because it isolates the issue. If the sensor works correctly with another board, then we know the problem is likely with the MIMXRT1180-EVK's setup or its interaction with the sensor. The FRDM-K64F successfully transmitted the 5x 0xFF on MOSI, which was verified using a logic analyzer. This crucial piece of evidence strongly suggests that the issue lies within the MIMXRT1180-EVK's hardware configuration, the Zephyr RTOS configuration for this board, or the LPSPI driver implementation on this specific platform. The logic analyzer output from the FRDM board clearly showed the expected 0xFF sequence on MOSI, a stark contrast to what was observed on the MIMXRT1180-EVK.

Impact and Environment: Setting the Stage

This LPSPI malfunction has a tangible impact. It's a functional limitation, meaning some features aren't working as expected, though the system remains usable to some extent. It's like having a car that can drive but the radio doesn't work—you can still get from point A to point B, but the experience isn't optimal. The environment in which this issue was observed includes:

  • Zephyr RTOS: Version 4.2.99 (a development snapshot of the upcoming 4.3 release)
  • SDK: Zephyr SDK 0.17.2

Understanding the environment is crucial because software versions and SDKs can have their own quirks and known issues. Knowing this context helps narrow down the potential causes and solutions.

Diving Deeper: Potential Causes and Troubleshooting Steps

Okay, guys, so we've laid out the symptoms and the environment. Now let's put on our detective hats and explore the possible culprits behind this LPSPI mystery. Here’s a breakdown of potential causes and how we might tackle them:

1. Pin Configuration Problems

  • The Suspect: Incorrect pin muxing or configuration in the device tree overlay.
  • The Investigation: Double-check the device tree overlay file for the MIMXRT1180-EVK. Ensure that the LPSPI3 pins (MOSI, MISO, SCK, and CS) are correctly assigned and configured. A tiny typo or a missed setting can lead to big headaches. Verify that the pin configurations match the hardware schematics and the sensor's requirements. Are the pull-up/pull-down resistors configured correctly? Is the SPI mode (clock polarity and phase) set appropriately?

2. Clocking Issues

  • The Suspect: Although the clock signal appears to be present at 4MHz, there might be subtle issues with the clock source, dividers, or gating.
  • The Investigation: Dive into the clocking configuration for the LPSPI3 peripheral. Are the clock dividers set correctly? Is the clock source stable and within the required frequency tolerance? Use a debugger to inspect the clock registers and verify that they are configured as expected. Sometimes, the issue isn't the clock frequency itself, but the clock's quality or stability.

3. DMA (Direct Memory Access) Problems

  • The Suspect: If DMA is being used for SPI transactions, there could be issues with the DMA configuration or transfer setup.
  • The Investigation: Check if DMA is enabled for LPSPI3. If so, verify the DMA channel assignments, buffer addresses, and transfer sizes. DMA issues can lead to data corruption or incomplete transfers, which might explain the garbled MOSI/MISO signals and the non-empty buffers. Ensure the DMA controller is properly initialized and that there are no conflicts with other peripherals using DMA.

4. Driver Bugs

  • The Suspect: A potential bug in the NXP LPSPI driver implementation within Zephyr.
  • The Investigation: This is where things get a bit more challenging. We might need to delve into the driver source code itself. Look for any known issues or errata related to the LPSPI driver for the MIMXRT1180. Check the Zephyr project's issue tracker and mailing lists for similar reports. Try stepping through the driver code with a debugger to see where the data transmission goes awry. Is the data being loaded into the SPI transmit buffer correctly? Are the SPI control registers being programmed as expected?

5. Hardware Issues

  • The Suspect: Although less likely, there could be a hardware problem with the MIMXRT1180-EVK board itself or the connections to the ADC.
  • The Investigation: Inspect the board for any physical damage or loose connections. Use a multimeter to check the continuity of the SPI lines between the microcontroller and the ADC. If possible, try a different MIMXRT1180-EVK board to see if the issue persists. Hardware problems can be tricky to diagnose, but a thorough physical inspection is always a good starting point.

6. SPI Mode Mismatch

  • The Suspect: The SPI mode (clock polarity and phase) configured in the driver might not match the requirements of the AD7194 ADC.
  • The Investigation: Consult the AD7194 datasheet to determine the correct SPI mode. Verify that the spi_config structure in the Zephyr driver is configured accordingly. An SPI mode mismatch can lead to incorrect data sampling and transmission.

7. Power Supply Issues

  • The Suspect: Insufficient or noisy power supply to the ADC or the MIMXRT1180-EVK.
  • The Investigation: Ensure that the power supply voltage is within the specified range for both the microcontroller and the ADC. Check for excessive ripple or noise on the power supply lines. A stable power supply is crucial for reliable SPI communication.

Next Steps: Let's Roll Up Our Sleeves

So, where do we go from here? Here’s a plan of action:

  1. Pin Configuration Audit: We’ll start by meticulously reviewing the device tree overlay to ensure the pin muxing and configurations are spot-on.
  2. Clocking Deep Dive: We'll then investigate the clocking setup for LPSPI3, verifying the clock source, dividers, and stability.
  3. Logic Analyzer Recon: Back to the logic analyzer! We'll capture SPI transactions in detail, paying close attention to the MOSI, MISO, and clock signals. This will give us a visual representation of what's happening on the wire.
  4. Driver Debugging: If the hardware checks pass, we’ll step through the NXP LPSPI driver code, using a debugger to trace the data flow and identify any potential bugs.

Wrapping Up: Stay Tuned!

This LPSPI issue on the MIMXRT1180-EVK is a classic example of the kind of challenges you might encounter in embedded systems development. But don't worry, guys! By systematically investigating the potential causes and using the right tools, we can crack this case. We hope this deep dive has been helpful, and we encourage you to share your own experiences and insights in the comments below. Stay tuned for updates as we continue our investigation. Happy debugging!