FUSE / CUSE kernel driver dissection notes

What this post is about Before anything: If you’re planning on using FUSE / CUSE for an application, be sure to read this first. It also explains why I bothered looking at the kernel code instead of using libfuse. So these are some quite random notes I took while trying to figure out how to [...]

FUSE / CUSE signal handling: The very gory details

First: If you’re planning on using FUSE / CUSE for an application, be sure to read this first. It also explains why I didn’t just take what libfuse offered. Overview This is a detour from another post of mine, which dissects the FUSE / CUSE kernel driver. I wrote this separate post on signal handling [...]

Linux CUSE (and FUSE): Why I ditched two months of work with it

Introduction If you’re planning to use CUSE (or FUSE) for an application you care about, this post is for you. That includes future self. I’m summarizing my not-so-pleasant journey with this framework here, with focus on how I gradually realized that I should start from the scratch with an old-school kernel module instead. Most important, [...]

xhci_hcd WARN Event TRB for slot x ep y with no TDs queued

What’s this? There’s a chance that you’re reading this because the message in the title appeared (or flooded) your kernel log. This post attempts to clarify what to do about it, depending on how much you want to get involved in the matter. So the short answer: The said warning message is a bug related [...]

Linux: Atheros QCA6174′s Bluetooth disappearing after reboot

When Bluetooth goes poof Having rebooted my computer after a few months of continuous operation, I suddenly failed to use my Bluetooth headphones. It took some time to figure out that the problem wasn’t with the Cinnamon 3.8.9 fancy stuff, nor the DBus interface, which produced error messages. There was simply no Bluetooth device in [...]

5 GHz Wifi access point on Linux Mint 19 / Atheros

+ how to just compile an Ubuntu distribution kernel without too much messing around. Introduction It’s not a real computer installation if the Wifi works out of the box. So these are my notes to self for setting up an access point on a 5 GHz channel. I’ll need it somehow, because each kernel upgrade [...]

Xilinx’ Zynq Z007s: Is it really single core?

Introduction Xilinx’ documentation says that XC7Z007S, among other “S” devices, is a single-core device, as opposed to, for example, its older brother XC7Z010, which is dual-core. So I compared several aspects of the PS part of a Z007S vs. Z010, and to my astonishment, I found that Z007S is exactly the same: Two CPUs are [...]

Soft Linux kernel hacking for dumping ULPI commands to USB PHY

Ever wanted to see how the a Linux USB host talks with its PHY with ULPI commands? Probably not. But if you do, here’s how I did it on a Zynq device, connected to an USB3320 USB 2.0 PHY chip. Note that: The relevant sources must be compiled into the kernel. Modules are loaded too [...]

Lubuntu 16.04 on ARM: Turning off the “Suspend” etc. options

In short On an embedded ARM-based Lubuntu 16.04, I had LXDE’s logoff dialog window offering suspend as an option, and when that was chosen, the system got itself into some nasty state with network and keyboard off. The serial console was still active, and yet, I was better off without it. It turned out that [...]

NXP / Freescale SDMA and the art of accessing peripheral registers

Preface While writing a custom SDMA script for copying data arriving from an eCSPI peripheral into memory, it occurred to me that there is more than one way to fetch the data from the peripheral. This post summarizes my rather decisive finding in this matter. Spoiler: Linux’ driver could have done better (Freescale’s v4.1.15) I’ve [...]