Marcus Folkesson

Embedded Linux Artist

An attempt to learn blindfolded chess

An attempt to learn blindfolded chess This is one of my more unusual projects, but I still think it is worth sharing. First of all, I do not consider myself as a skilled chess player. I would not say that I'm bad, but I have a lot more to learn. My ELO at Lichess is about 1400. I have played chess since I was a kid, but I have never been serious about it.

cover

Posted by Marcus Folkesson on Friday, March 7, 2025

Lets talk about ECC and NAND flashes

Lets talk about ECC and NAND flashes Raw NAND flashes is not that common these days. At least not in those projects I have been working with for the last ~8 years. They seems to have been replaced by eMMC for many applications, but there are still some use cases where raw NAND flashes are prefered. In this blog post, we will talk a little about Error Correcting Code (ECC) and NAND flashes as that is such a critical part of the NAND flash technology.

cover

Posted by Marcus Folkesson on Thursday, January 30, 2025

Repair of Sennheiser Momentum True Wireless earbuds

Repair of Sennheiser Momentum True Wireless earbuds I have a pair of Sennheiser Momentum True Wireless (MTW3) earbuds that had been lost for a while. Once I found them, they had been laying around for a while and the battery was completely drained. I tried to charge them, but they did not charge at all. They are completely dead. Here they are. What I could see, there was no obvious way to open them up.

cover

Posted by Marcus Folkesson on Friday, January 10, 2025

Don't forget the Jira tag in your git message

Don't forget the Jira tag in your git message I keep forgetting to add the Jira tag in my git messages. This is a problem as we use Jira for our project management and the Jira tag is used to link the commit to the issue. It is simply hard to get into my workflow for some reason. Some time ago, I wrote about pre-commit [1], a framework for managing and maintaining pre-commit hooks for git.

cover

Posted by Marcus Folkesson on Thursday, January 9, 2025

Control of my geothermal heat pump

Control of my geothermal heat pump The electicity price in Sweden varies a lot during the day. It's usually cheapest during the night and most expensive during the day, but not always. One day a week ago, it was not much wind in Germany and therefore we exported electricity there which resulted in very high prices here in Sweden. 1 kWh cost over 10 SEK (almost 1 USD per kWh) for a few hours, this excluding transmission fees and taxes.

cover

Posted by Marcus Folkesson on Thursday, December 19, 2024

UBI volumes in Yocto

UBI volumes in Yocto These days, managed NAND flash memories such as eMMC or SD-cards has become more common in the embedded Linux systems as they abstract (or hide..) the complicated raw NAND memory under the hood. Even if raw NAND memories are more complicated to handle, they are still used in many new products out there. When working with raw NAND flashes, UBI [1] with UBIFS on top of that is the way to go.

cover

Posted by Marcus Folkesson on Saturday, December 14, 2024

Remoteproc, rpmsg and SYSBIOS

Remoteproc, rpmsg and SYSBIOS I'm currently working with a couple of SoCs (OMAPL-138, DRA7xx) from Texas Instruments where both has an C6xx DSP core along with the ARM core. This is no unusual configuration, many modern SoCs today have heterogeneous remote processor devices in asymetric multiprocessing (AMP) configurations like these two. In this case, the DSP-cores where supposed to run SYS/BIOS with the TI IPC MessageQ stack to communicate with the ARM core.

cover

Posted by Marcus Folkesson on Thursday, December 5, 2024

Detect time jumps in Linux

Detect time jumps in Linux Recently I had a case where the application created multiple timers for different events. After the timers was created, the NTP client updates the system time resulting in that all timers being off and needing to be adjusted. Adjust the timers is one thing, but how do we detect the time jump? It's not the first time I'm in a situation where I have to deal with such time jumps, I guess it's quite a common case, so why not write a few words about it?

cover

Posted by Marcus Folkesson on Monday, November 11, 2024

TIL - suid_dumpable

TIL - suid_dumpable 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 Ever notice that you can't get a coredump from a process running with extra privileges like capabilites or setuid? This is related to a previous post [1] about some restrictions that is applied to such processes. I suggest to read that post first to get the context.

Posted by Marcus Folkesson on Tuesday, October 22, 2024

Protected FIFOs and regular files

Protected FIFOs and regular files Since version 4.19 [1], Linux has the default behaviour to prevents opening of regular files and FIFOs that is not owned by the user in world writable sticky directories. Example on such directory is /tmp/ which usually has the sticky bit set. This may sound obvious, but what is not so obvious is that this restriction also applies to the root user. You can therefore end up in a situation where e.

cover

Posted by Marcus Folkesson on Monday, October 21, 2024