Скачать или смотреть Solving mmap Failures with Libcamera on Raspberry Pi 3B

Discover how to troubleshoot `mmap` failures when working with Libcamera on Raspberry Pi 3B. Learn effective solutions to resolve invalid argument errors!
---
This video is based on the question https://stackoverflow.com/q/76270783/ asked by the user 'jiandingzhe' ( https://stackoverflow.com/u/1484850/ ) and on the answer https://stackoverflow.com/a/76294027/ provided by the user 'jiandingzhe' ( https://stackoverflow.com/u/1484850/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: mmap failed on libcamera returned frame data

Also, Content (except music) licensed under CC BY-SA https://meta.stackexchange.com/help/l...
The original Question post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license, and the original Answer post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license.

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
Understanding the mmap Failure Issue in Libcamera

If you're working with camera operations on a Raspberry Pi 3B and using libcamera, you might have encountered an error that says mmap failed on libcamera returned frame data. This error can signal a frustrating roadblock for developers. The failure can happen after one or two successes and comes with an important log that indicates the specifics of the failure.

In this guide, we will explore the underlying causes of this error in detail and provide you with a structured solution to help you overcome it. So, let’s dive in!

The Problem: mmap Failing

In your code, you are utilizing mmap to access frame data returned by libcamera. Your implementation might look something like this:

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

The Error Log

A typical output log that triggers this error might look like this:

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

According to man 2 mmap, the EINVAL error can be raised due to several conditions, such as:

Incorrect address, length, or offset.

Length being zero.

Incorrect flags set.

With the code checking out on these aspects, it leads you to ponder how to resolve this error effectively.

Solution: Understand Color Planes and DMA

A key insight shared by fellow developers on community forums suggests that the error you're encountering might stem from the way you're handling color planes in a frame buffer. This specific scenario often indicates that the planes are using the same DMA file descriptor.

The Fix: Mmap All at Once

Here’s the crux of the solution:

Single mmap for all Planes: Instead of calling mmap separately for each color plane in a frame buffer, you should mmap them all at once. This approach helps maintain proper alignment of offsets, which is crucial for successful memory mapping.

Why This Works: When you mmap color planes separately, the offsets of subsequent planes may not align with page boundaries, resulting in the mmap failure. By performing a single mmap operation encompassing all planes, you avoid these alignment issues.

Example Code Adjustments

You might need to refactor your code structure to implement this as follows:

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

Conclusion

Dealing with mmap failures can be daunting, especially in complex scenarios involving multiple data planes and DMA. By understanding the root cause of the Invalid argument error and adjusting your mmap strategy, you can streamline your camera operations on the Raspberry Pi 3B using libcamera.

With this approach, you'll not only mitigate the error but also enhance your project’s efficiency!

Happy coding!