Workaround for creating bootable FAT partition for Beagle Bone / AM335x on recent distros

On recent GNU/Linux distributions such as Ubuntu 22.04 and 22.10, you may hit an issue creating a bootable FAT partition for embedded boards, at least with the TI AM335x processor, such as the 32 bit Beagle Bone boards.

So, suppose you plugged your SD card in a USB card reader, and your SD card is associated to the /dev/sdb block device file (for example).

Here’s the command that no longer works:

mkfs.vfat -F 32 -n boot /dev/sdb1

This happened to me while porting the new version of our embedded Linux course to the BeagleBone Black board, using Ubuntu 22.04 as the host platform.

If you prepare an SD card, create a bootable partition, format it with the FAT32 filesystem with the above command, copy a bootloader to this partition, the romcode in the TI AM335x chip won’t recognize it and your board will remain completely silent.

I investigated the problem and found that it happens with mkfs.vfat version 4.2 released on 2021-01-31, and which is shipped in recent GNU/Linux distributions such as Ubuntu 22.04 and 22.10.

Looking at the source code didn’t help right away, but I eventually found a dosfstools bug report which explains the cause of this issue.

Thanks to this bug report and its associated comment thread, an easy workaround was found. You just need to add the -a option to the mkfs.vfat command line:

mkfs.vfat -a -F 32 -n boot /dev/sdb1

I eventually also realized that the issue doesn’t happen if you access the SD card through a regular MMC/SD slot which has the device represented as a /dev/mmcblk device.

So, if your computer has such a slot as most do, you can just use the regular command without the -a option:

mkfs.vfat -F 32 -n boot /dev/mmcblk0p1

In my case, I was using an external USB card reader because I was running experiments from a VirtualBox virtual machine. I didn´t know how to access my host’s MMC/SD card reader from the VM, but accessing a USB device was very straightforward.

Why the difference? That’s because the MMC/SD interface exposes different information from what a USB mass storage device does. That’s a different interface.

The issue is also reported on the TI AM3874 chip. Don’t hesitate to post a comment here if you have a board with yet another TI chip that is impacted too. This could help other users.

Welcome to Jérémie Dautheribes

Welcome on board!Bootlin is really happy to welcome another engineer in its team: Jérémie Dautheribes, who joined us on November 2, 2022.

Jérémie Dautheribes graduated in 2020 with a master degree in Ambiant, Mobile and Embedded Systems from the Toulouse University. After graduating, he worked at the french research institute INRIA on cache optimization for FreeRTOS multicore programs, and then in a company called EPSI where he was in charge of developing and maintaining Linux-based BSPs for i.MX6 and Tegra platforms, based on Yocto.

In addition, Jérémie has some experience in using the Rust programming language for low-level development, a skill that might prove to be useful for doing Linux kernel development in the future!

Jérémie is now joining our team located in Toulouse, France, where he will work at our office with Hervé Codina, Paul Kocialkowski, Köry Maincent, Thomas Perrot, Miquèl Raynal and Thomas Petazzoni.

For more details, see Jérémie’s page on and his LinkedIn profile.

New training course: Linux debugging, profiling, tracing and performance analysis

Since its inception, Bootlin has offered training courses on technical topics related to the use of Linux in embedded systems, with freely accessible training materials, and trainers with in-depth and real-life experience in their field. Based on these ideas, we have progressively extended our training portfolio over the years.

Today, we are extremely happy to announce a brand new course: Linux debugging, profiling, tracing and performance analysis. Many of our customers working on embedded Linux systems have expressed interest in diving into these complex topics, so we’ve created this course to:

  1. Give enough background information about how Linux works to be able to have a solid reasoning when investigating performance issues or simply bugs. Our course therefore details how user-space vs. kernel-space works, scheduling, and memory management, as a prerequisite to understanding better how Linux works.
  2. Give a strong introduction to the most important debugging, profiling and tracing tools in Linux, which are often not easy to get started with. We cover a very large spectrum of tools: strace, gdb, perf, ftrace, LTTng, kgdb, kmemleak, and many more. All these tools are illustrated through practical examples.

See the complete agenda for this course: debugging-online-agenda.pdf. The complete training materials will be freely available after the first session has been delivered, end of November 2022.

This course is currently being prepared by Bootlin engineer Clément Léger, who will also be teaching this course. Clément has a deep knowledge of how CPUs work and how Linux runs on a given CPU architecture, by having ported the Linux kernel to a brand new CPU architecture.

While the first session of this course will be delivered to a private customer, we have already scheduled a first public session which will take place on January 30, 31, Feb 1, 2, 2023, plus an extra session on Feb 3, 2023 if needed to cover all topics/questions. This session will take place each day from 14:00 to 18:00 UTC+1 (Paris time). Registration takes place directly online: the pricing is 569 EUR per seat at the discounted rate, or at 669 EUR per seat at the normal rate.

We can also organize a private session of this course for your team/company, either on-line or on-site: contact us to request a quote if you’re interested.

Linux 6.0 released, Bootlin contributions

Linux 6.0 has been released two weeks ago, and Linux 6.1-rc1 is already out of the door, but we didn’t get the chance to look at the contributions made by Bootlin to the Linux 6.0 release. Before we do that, let’s provide our usual must-read articles on Linux 6.0: the Linux 6.0 merge window part 1 and Linux 6.0 merge window part 2 articles and the article.

On Bootlin side, our significant contributions to this release have been:

  • Clément Léger contributed a new driver for the Ethernet switch found in the Renesas RZ/N1 processor, as well as a PCS driver for the MII converter of the same processor. Obviously, this came with the related Device Tree bindings and Device Tree changes, but also with a few small changes in the DSA subsystem.
  • Hervé Codina enabled support for the PCIe controller found in the same Renesas RZ/N1 processor, which in fact does not allow to use PCIe devices, but USB devices: this PCIe controller is only used to connect to an internal USB controller in the chip, which therefore allows to use USB devices.
  • Köry Maincent extended the existing mpc4922 DAC IIO driver to also support the mpc4921 variant, which has only one output channel instead of two.
  • Luca Ceresoli contributed several improvements to the I2C subsystem documentation.
  • Paul Kocialkowski contributed a new DRM driver for the logiCVC-ML display controller IP
  • Paul Kocialkowski contributed two new V4L drivers for the MIPI CSI-2 camera interfaces available in the Allwinner A31 family of processors (sun6i) and the Allwinner A83T family of processors (sun8i).

Here is the full details of our contributions, commit by commit:

Yocto Project: quickest instructions to generate BeagleBone images

Here are the quickest instructions (I hope) for having the Yocto Project build an embedded Linux image for BeagleBone boards based on the TI AM335x CPU:

git clone -b kirkstone
source poky/oe-init-build-env

This gets you in a new build directory. You can then generate your image:

MACHINE="beaglebone-yocto" bitbake core-image-minimal

Once the build is over, you can flash the image on a microSD card (assuming it’s mapped to /dev/mmcblk0):

cd tmp/deploy/images/beaglebone-yocto
dd if=core-image-minimal-beaglebone-yocto.wic of=/dev/mmcblk0 bs=4M

More details for customizing images and supporting other boards in the Yocto Project manual.BeagleBone Black board booting on an embedded Linux root filesystem built by the Yocto Project