Troubleshooting USBIP Errors With WebUSB Sample In Zephyr RTOS

by StackCamp Team 63 views

Hey guys! Ever run into a snag where your USB just doesn't want to play nice? Today, we're diving deep into a specific issue encountered while using usbip with the samples:subsys:usb:webusb in Zephyr RTOS. Specifically, we're tackling a bug where the system continuously receives data instead of behaving like a proper Sender and Receiver. Let's break it down and see how we can fix it!

Understanding the Issue: Continuous Data Reception

The core problem we're addressing is that when using USBIP, the device under test continuously receives data. Ideally, in a Sender-Receiver setup, you'd expect a controlled exchange of information. But what happens when data just keeps pouring in? That's exactly what we're seeing here, and it throws a wrench in the works for reliable USB communication.

This continuous data reception issue was observed using the latest commit of Zephyr RTOS, indicating it's a recent occurrence or a persistent problem not yet resolved in the codebase. This means we're working with fresh code, which is both exciting and potentially challenging, as we might be among the first to encounter this particular bug in this context.

Regression Check

Before we get too far down the rabbit hole, it's crucial to check if this is a regression. A regression means the issue was working fine in a previous version but is now broken. In this case, it's marked as "This is a regression," which makes troubleshooting a bit more focused. Knowing it was once working gives us a baseline and suggests that a recent change likely introduced the bug.

Steps to Reproduce

To really get our hands dirty, we need to reproduce the issue consistently. Here's how you can replicate the bug:

  1. Initial Setup:

    • Follow the Zephyr documentation for networking with native simulation. This involves setting up the environment to simulate network connections, which is vital for testing embedded systems without physical hardware.

    • Use the following command to build the sample:

      west build -b native_sim/native/64 samples/subsys/usb/webusb -- -DSNIPPET=usbip-native-sim

      This command tells the West build tool to compile the webusb sample for a native simulation environment with USBIP support.

    • Run the built executable with sudo ./build/zephyr/zephyr.exe. Running with sudo is often necessary for accessing hardware resources or setting up network interfaces.

  2. USBIP Configuration:

    • Consult the Zephyr documentation on USB host with USBIP for the next steps. This documentation provides the specific instructions for configuring USBIP to work with Zephyr, ensuring the simulated USB device can be accessed over the network.

  3. List Exportable USB Devices:

    • Use the command sudo usbip list -r 192.0.2.1 to list USB devices available for attachment via USBIP. The IP address 192.0.2.1 is a common example IP used in documentation and testing environments.
    • The output should show the Nordic Semiconductor device, which is essential for proceeding with the test.

  4. WebUSB Demo:

    • Open the test page (https://docs.zephyrproject.org/latest/samples/subsys/usb/webusb/demo.html) in a web browser. This page provides a user interface to interact with the WebUSB device.
    • Click "Connect To WebUSB Device" and select the USBD sample item. This establishes a connection between the web application and the emulated USB device.
    • Click "Send WebUSB!". This action triggers the data transmission that should demonstrate the Sender-Receiver functionality.

Log Output Analysis

The provided log output gives us a peek into what's happening under the hood. Let's dissect it:

  • WARNING: Using a test - not safe - entropy source: This is a common warning in testing environments where a secure random number generator isn't crucial. We can safely ignore it for this issue.
  • *** Booting Zephyr OS build v4.2.0-5168-g491498ab9e30 ***: This line confirms the Zephyr OS version and build hash, which can be useful for tracking down specific changes.
  • [00:00:00.000,000] <inf> net_config: Initializing network: The system is initializing the network stack, which is necessary for USBIP to function.
  • [00:00:00.000,000] <inf> net_config: IPv4 address: 192.0.2.1: The device has been assigned the IP address 192.0.2.1, which matches the one used in the usbip list command.
  • [00:00:00.000,000] <inf> main: USBD message: Bus reset: A USB bus reset occurs, which is a normal part of device initialization.
  • [00:00:00.055,001] <inf> sfunc: Configuration enabled: The USB configuration is enabled, indicating the device is ready to operate.
  • [00:00:00.055,001] <inf> main: USBD message: New device configuration: A new USB device configuration is being used.
  • [00:00:30.901,001] <inf> main: Vendor callback to host: A vendor-specific callback is being made to the host.
  • [00:00:30.901,001] <inf> main: Get MS OS 2.0 Descriptor Set: The system is attempting to retrieve the Microsoft OS 2.0 Descriptor Set, which is used for compatibility and feature advertisement.
  • The repetitive lines starting with [00:00:47.201,001] <inf> sfunc: Transfer finished... are the most telling. They show continuous data transfers happening on endpoint 0x01 (OUT endpoint) and 0x81 (IN endpoint). The fact that these transfers occur repeatedly without a clear stop condition indicates the continuous data reception issue we're investigating.

Potential Causes and How to Tackle Them

Okay, so we've got the problem nailed down. Now, what could be causing this, and how do we even begin to fix it? Here are some potential culprits and strategies:

1. Endpoint Configuration Issues

The USB endpoints are the channels through which data is sent and received. An incorrect configuration could lead to an endpoint continuously listening for data, even when it shouldn't be.

  • How to Tackle:
    • Double-check the endpoint descriptors: Verify that the endpoint descriptors in the device firmware are correctly configured. This includes the endpoint type (bulk, interrupt, isochronous), direction (IN/OUT), and maximum packet size.
    • Look for any misconfigurations: Pay special attention to any flags or settings that might cause the endpoint to remain active indefinitely.

2. Driver or Firmware Bugs

Bugs in the USB driver or the device firmware can lead to unexpected behavior, such as continuously receiving data.

  • How to Tackle:
    • Review the driver code: Examine the USB driver code for any potential bugs, such as infinite loops or incorrect state management.
    • Inspect the firmware: Similarly, review the device firmware for any issues that might cause it to continuously request or receive data.
    • Use a debugger: Employ a debugger to step through the code and observe the data flow. This can help pinpoint exactly where the continuous reception is originating.

3. USBIP Implementation Quirks

USBIP virtualizes USB devices over a network, which can introduce its own set of challenges. There might be specific issues in the USBIP implementation that are causing the continuous data flow.

  • How to Tackle:
    • Examine USBIP-specific code: Investigate the USBIP-related code in Zephyr to identify any potential problems. This could involve looking at how USB requests are handled over the network.
    • Check for known USBIP issues: Consult the USBIP documentation and community forums for any known issues or workarounds related to continuous data reception.

4. Race Conditions or Interrupt Handling

Race conditions or incorrect interrupt handling can sometimes lead to data being processed multiple times or endpoints not being properly managed.

  • How to Tackle:
    • Analyze interrupt routines: Carefully examine the interrupt routines related to USB data transfer. Ensure that interrupts are being handled correctly and that there are no race conditions.
    • Use synchronization primitives: Employ synchronization primitives (like mutexes or semaphores) to protect shared resources and prevent race conditions.

5. WebUSB Layer Issues

Since we're using WebUSB, there's a possibility that the issue lies in the WebUSB layer itself. Problems in how data is being sent or received via WebUSB could manifest as continuous reception.

  • How to Tackle:
    • Review WebUSB code: Inspect the code that handles WebUSB communication in the device firmware.
    • Use debugging tools: Utilize browser developer tools to monitor the data being sent and received via WebUSB. This can help identify any discrepancies or unexpected behavior.

Diving Deeper into the Steps to Reproduce

To effectively troubleshoot, let's revisit the steps to reproduce the bug and see if we can glean any more insights.

1. Setting Up the Environment

The initial setup involves building Zephyr for the native_sim target. This target is designed to run Zephyr as a native application on your development machine, which simplifies debugging since you can use standard debugging tools.

The key here is ensuring that the networking is correctly configured. The 192.0.2.1 IP address is crucial, and any misconfiguration in the network setup can prevent USBIP from working correctly.

2. Configuring USBIP

Configuring USBIP is where things can get a bit tricky. You need to ensure that the USBIP kernel modules are loaded and that the USB device is correctly exported. This typically involves using commands like usbipd (the USBIP daemon) and usbip. Make sure these are correctly installed and running.

3. WebUSB Connection

The WebUSB connection is established via a web page. This means the browser needs to support WebUSB, and you might need to grant permissions for the page to access USB devices. If the connection isn't established correctly, no data will flow, but if there's a continuous reception issue, you'll see it once the connection is up.

Interpreting the Log Output in Detail

The log output is our primary source of information. The repetitive Transfer finished messages are the smoking gun, but let's break down what they mean:

  • Transfer finished 0x434620 -> ep 0x01, len 7, err 0: This line indicates that a transfer finished on endpoint 0x01 (OUT endpoint), with a length of 7 bytes and no error (err 0). This suggests that the device is successfully receiving data.
  • Transfer finished 0x434620 -> ep 0x81, len 0, err 0: This line shows a transfer finished on endpoint 0x81 (IN endpoint), with a length of 0 bytes and no error. This means the device is trying to send data, but nothing is being sent.

The continuous repetition of these lines, particularly the transfers on the OUT endpoint (0x01), points to the device continuously receiving data without properly processing or stopping the reception.

Impact and Environment

The impact of this bug is classified as a "Functional Limitation," meaning some features aren't working as expected, but the system is still usable. This is important because it helps prioritize the issue relative to other bugs. A functional limitation might not be as critical as a system crash, but it still needs to be addressed for a fully functional system.

The environment information is also crucial. The bug is occurring on Debian 13 with a specific SHA of the Zephyr codebase. This allows other developers to reproduce the issue in the same environment, ensuring consistency in troubleshooting.

Conclusion: Let's Get This Fixed!

So, there you have it! We've dissected the bug, understood the steps to reproduce it, and explored potential causes. The continuous data reception issue in the WebUSB sample when using USBIP is a tricky one, but by systematically analyzing the logs, the code, and the environment, we can get to the bottom of it.

Now it’s your turn! Dive into the Zephyr codebase, play around with the USBIP configuration, and let's squash this bug together. Remember, every line of code you examine and every test you run brings us one step closer to a solution. Happy debugging, and let's make Zephyr even more awesome!