Marcus Folkesson

Embedded Linux Artist

Route priorities - metric values

Route priorities - metric values Brief It's not an uncommon scenario that a Linux system has several network interfaces that are all up and routeable. For example, consider a laptop with both Ethernet and WiFi. But how does the system determine which route to use when trying to reach another host? I was up to setup a system with both a 4G modem and a WiFi connection. My use case was that when the WiFi is available, that interface should be prioritized over 4G.

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Posted by Marcus Folkesson on Sunday, June 11, 2023

Lund Linux Conference 2023

Lund Linux Conference 2023 The conference Lund Linux Conference (LLC) [1] is a "half-open" conference located in Lund. It's a conference with high quality and I appreciate that the athmosphere is more familiar than at the larger conferences. I've been at the conference a couple of times before and the quality on the talks this year was as good as usual. ( The talks are by the way available on Youtube [3].

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Posted by Marcus Folkesson on Thursday, May 25, 2023

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 fourth post in this series. See also part part1, part2 and part3. Overview This is the fourth 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 contributions are 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 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 who simply bypass the system and access the data storage directly is encryption. Let's say that we encrypt our sensitive data.

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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 have 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 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 wrote 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 information in the IP header for each packet.

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Posted by Marcus Folkesson on Friday, February 17, 2023