Marcus Folkesson

Embedded Linux Artist

Write a device driver for Zephyr - Part 1

Write a device driver for Zephyr - Part 1 This is the first post in this series. See also part part2, part3 and part4. Overview The first time I came across Zephyr [1] was on Embedded Linux Conference in 2016. Once back from the conference I tried to install it on a Cortex-M EVK board I had on my desk. It did not go smoothly at all. The documentation was not very good back then and I don't think I ever got system up and running.

Posted by Marcus Folkesson on Wednesday, April 19, 2023

Write a device driver for Zephyr - Part 2

Write a device driver for Zephyr - Part 2 This is the second post in this series. See also part part1, part3 and part4. Overview In the first part1 of this series, we did setup the hardware and prepared the software environment. In this part we will focus on pretty much everything but writing the actual driver implementation. We will touch multiple areas in order to fully integrate the driver into the Zephyr project, this includes:

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Posted by Marcus Folkesson on Wednesday, April 19, 2023

Write a device driver for Zephyr - Part 3

Write a device driver for Zephyr - Part 3 This is the third post in this series. See also part part1, part2 and part4. Overview In the previous part we prepared Zephyr for our soon to be born driver. Now we have finally come to the fun point - write the actual driver code! Driver API I used to write code for the Linux kernel which is a little bit more complex kernel than Zephyr.

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Posted by Marcus Folkesson on Wednesday, April 19, 2023

Write a device driver for Zephyr - Part 4

Write a device driver for Zephyr - Part 4 This is the forth post in this series. See also part part1, part2 and part3. Overview This is the forth and last part of this series where we will focus on contribute the driver back to the Zephyr project. Zephyr use Github for hosting the project and all contribution is by Pull Requests. The process is all well documented [1], both on how to contribute but also what the project expect from you as a contributor.

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Posted by Marcus Folkesson on Wednesday, April 19, 2023

Encrypted storage on i.MX

Encrypted storage on i.MX Brief Many embedded Linux systems does have some kind of sensitive information on a file storage. It could be private keys, passwords or whatever. It's always a risk that this information could be revealed by an unauthorized person that got their physical hands on the device. The only protection against attackers that who simply bypass the system and access the data storage directly is encryption.

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Posted by Marcus Folkesson on Monday, April 3, 2023

Bug in the iMX8MP ECSPI module?

Bug in the iMX8MP ECSPI module? Background I do have a system where I can swap between iMX8M Mini and iMX8M Plus CPU modules on the same carrier board. I did write a a SPI driver for a device on the carrier board. The device is connected to the ECSPI1 (the CPU contains several ECSPI modules) and use the hardware chipselect 0 (SS0). The driver has been used with the iMX8MM CPU module for a while, but as soon I swapped to the iMX8MP it certainly stopped working.

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Posted by Marcus Folkesson on Tuesday, March 21, 2023

Capture an image with V4L2

Capture an image with V4L2 Brief As we has seen before, cameras in Linux could be a complex [1] story and you have to watch every step you take to get it right. libcamera [2] does a great job to simplify this in a platform independent way and should be used whenever it's possible. But not all cameras does have a complex flow-chart. Some cameras (e.g. web cameras) are "self-contained" where the image data goes straight from the camera to the user application, without any detours through different IP blocks for image processing on its way.

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Posted by Marcus Folkesson on Sunday, March 19, 2023

Route traffic with NAT

Route traffic with NAT Long time ago I wrota a blog post [1] about how to use NAT to route traffic to your embedded device via your host computer. Back then we were using iptables to achieve it, nowadays nftables is the preferred successor, so it's time for an update. What is NAT anyway? Network Address Translation, or NAT, does map an address space into another by modifying the network address infromation in the IP header for each packet.

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Posted by Marcus Folkesson on Friday, February 17, 2023

Contiguous Memory Allocator

Contiguous Memory Allocator Introduction I do find memory management as one of the most fascinating subsystem in the Linux kernel, and I take every chance I see to talk about it. This post is inspired by a project I'm currently working on; an embedded Linux platform with a camera connected to the CSI-2 bus. Before we dig into which problems we could trip over, lets talk briefly about how the kernel handles memory.

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Posted by Marcus Folkesson on Monday, February 6, 2023

Use custom EDID in Linux

Use custom EDID in Linux Extended Display Identification Data (EDID) is a metadata format for display devices to describe their capabilities such as resolution, display size, timing, bit depth and update frequency. It's a 128-byte (EDID) or 256-byte (Enhanced-EDID) structure transferred from the display device over the Display Data Channel (DDC) protocol, which is a layer on top of the I2C specification. The EDID is accessible via the I2C address 0x50 and can usually be read even if the display is turned off, which is quite nice.

Posted by Marcus Folkesson on Saturday, January 7, 2023