Marcus Folkesson

Embedded Linux Artist

Leather watch strap keeper

Leather watch strap keeper My watch was missing the strap keeper, so I had to make one. To be honest, I did not put my soul into this project, I had an urge to fix it while the food was getting ready in the oven. Anyway, here is my steps to make one. The steps Cut out a leather strap. My final size was about 14mm wide. Bevel the edges:

cover

Posted by Marcus Folkesson on Monday, February 13, 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.

cover

Posted by Marcus Folkesson on Monday, February 6, 2023

TIL - U-Boot support for HTTP

TIL - U-Boot support for HTTP TIL, Today I Learned, is more of a "I just figured this out: here are my notes, you may find them useful too" rather than a full blog post Until now, U-Boot did only support UDP and were limited to protocols that are based on that. In practice it meant that you were only able to use TFTP and NFS for network file transfer.

cover

Posted by Marcus Folkesson on Friday, January 27, 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

Audio and Embedded Linux

Audio and Embedded Linux Brief Last time I used wrote kernel drivers for the ASoC (ALSA System on Chip) subsystem, the functionality was split up into these parts: Platform class driver that defines the SoC audio interface for the actual CPU itself. This includes both the DAI (Digital Audio Interface) and any potential audio muxes (e.g. i.MX6 has its AUDMUX). CODEC class driver that controls the actual CODEC. Machine drivers that is the magic glue between the SoC and the CODEC which connect the both interfaces.

cover

Posted by Marcus Folkesson on Friday, December 23, 2022

Debug kernel with KGDB

Debug kernel with KGDB What is KGDB? KGDB intend to be used as a source code level debugger on a running Linux kernel. It works with GDB and allows the user to inspect memory, variables, setup breakpoints, step lines and instructions. Pretty much the same that all application developers are used to, but for the kernel itself. Almost every embedded Linux system does have a serial port available, and that is all that you need to connect GDB to your kernel.

cover

Posted by Marcus Folkesson on Saturday, December 17, 2022

TIL - Virtual CAN interfaces

TIL - Virtual CAN interfaces TIL, Today I Learned, is more of a "I just figured this out: here are my notes, you may find them useful too" rather than a full blog post There are many scenarios where a virtual Controller Area Network(CAN) interface could be handy. It let you develop and test applications that without an actual physical CAN bus. My scenario is to play around with Berkley Packet Filter(BPF) [1] and do some data manipulation on recieved CAN frames in kernel space.

Posted by Marcus Folkesson on Wednesday, November 30, 2022

Raspberry Pi and QEMU

Raspberry Pi and QEMU What is QEMU? QEMU is a generic and open source machine emulator and visualizer. It emulates full machines (boards) of different architectures and is useful for both application and kernel development. The CPU itself could be fully emulated (together with devices, memories and so on) or work with a hypervisor such as KVM or Xen. If support for your hardware is missing, then it's a fairly easy task to write a stub driver that your application can interface.

Posted by Marcus Folkesson on Tuesday, November 29, 2022

Crosscompile libcamera for RPi

Crosscompile libcamera for RPi Goal The goal is to cross-compile libcamera [1] and libcamera-apps [2] for Raspberry Pi using the latest Raspbian [3] (Bullseye) release. Usually you setup the root filesystem with Buildroot [4] or Yocto [5] and generate a SDK that you can use to compile your application. The Raspbian distribution does not come with a SDK so we have to setup our own. We will use a Raspberry Pi 3b for this.

cover

Posted by Marcus Folkesson on Tuesday, November 29, 2022

TIL - Debug FindBoost in CMake

TIL - Debug FindBoost in CMake TIL, Today I Learned, is more of a "I just figured this out: here are my notes, you may find them useful too" rather than a full blog post When you use find_package for a Boost component in CMake it will end up with the FindBoost.cmake [1] module. It is usually located in /usr/share/cmake/Modules/FindBoost.cmake. I had to debug a cross compile setup for an application using CMake, and the root file system did use wierd paths for everything.

Posted by Marcus Folkesson on Tuesday, November 29, 2022