Marcus Folkesson

Embedded Linux Artist

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

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

What is libcamera and why should you use it?

What is libcamera and why should you use it Read out a picture from camera Once in a time, video devices was not that complex. To use a camera back then, your application software could iterated through /dev/video* devices and pick the camera that you want and then immediately start using it. You could query which pixel formats, frame rates, resolutions and all other properties that are supported by the camera.

cover

Posted by Marcus Folkesson on Friday, November 25, 2022

HID report descriptors and Linux

HID report descriptors and Linux HID Devices USB HID (Human Interface Device) device class is the type of computer peripherals that human interacts with, such as keyboards, mice, game controllers and touchscreens. The protocol is probably one of the most simple protocols in the USB specification. Even if HID was originally written for USB in mind, it works with several other transport layers. Your mouse and keyboard do probably use HID over USB, the touchscreen in your smartphone could use HID over I2C.

cover

Posted by Marcus Folkesson on Saturday, October 15, 2022

Industrial I/O and triggers

Industrial I/O and triggers I've maintained a couple of IIO-drivers (MCP3911 [4] and LTC1660 [5]) for some time now and it's time to give at least the MCP3911 a face-lift. This time the face lift includes support for: Buffers Triggers Make the driver interrupt driven Add support for setting Oversampling Ratio Add support for setting PGA (Pre Gain Amplifier) Also clean it up a bit by only using device managed resources.

cover

Posted by Marcus Folkesson on Thursday, August 18, 2022

Mounting with systemd and udev

Mounting with systemd and udev Systemd hasn't always been my first choice as init system for embedded system, but I cannot ignore that it has many good and handy things that other init systems don't. At the same time, that is just what I don't like with systemd, it does not follow the "Do one thing and do it well"-philosophy that I like so much. I'm very thorn about it.

cover

Posted by Marcus Folkesson on Friday, August 12, 2022

GPLv2 and GPLv3

Open Source "Free as in freedom - not as in free beer". Free beer is nice, but freedom is even nicer. I have been working with companies from different sections including consumer electronics, military applications, automotive and aeronautics. One common question, regardless of section, is "Can we really use Open Source in our product?". The answer is usually Yes, you can, but.... One common misunderstanding is to interpret Open Source as in free beer.

cover

Posted by Marcus Folkesson on Thursday, February 10, 2022

This website setup

This website setup This post is more for my own good if I have to setup my website once again. Maybe someone find it useful. Tools Hugo I use Hugo [1] to generate my website. Hugo is a fantastic tool for generate static web pages in an flexible way. All pages is written in reStructured Text [2] which is the markup syntax I strongly prefer. Docker The web server [4] and traefik [5] server is running in docker [3] containers.

Posted by Marcus Folkesson on Wednesday, March 3, 2021