Crystalfontz boards support in Yocto

The Yocto 1.5 release is approaching and the Freescale layer trees are now frozen.
Free Electrons added support for the various Crystalfontz boards to that release as you can check on the OpenEmbedded metadata index.

Yocto Project

First some preparative work has been done in the meta-fsl-arm layer in order to add the required features to generate an image able to boot on the Crystalfontz boards:

  • Support for a newer version of the Barebox mainline, 2013.08.0. As the previously supported version of Barebox was too old, it didn’t include support for the Crystalfontz boards. Also, some work has been done to make the recipe itself more generic so that custom layers can reuse it more easily.
  • Inclusion of the patches allowing the imx-bootlets to boot Barebox. The imx-bootlets were only able to boot U-Boot or the Linux kernel until now.
  • Creation of a new image type, using the imx-bootlets, then Barebox to boot the Linux kernel. All the boards based on a Freescale mxs SoC (i.mx23 and i.mx28) will benefit of this new image type. This is actually the difficult part where you lay out the compiled binaries (bootloaders, kernel and root filesystem) in the final file that is an SD card image ready to be flashed.

Then, the recipes for the Crystalfontz boards have been added to the meta-fsl-arm-extra layer:

  • First the bootloaders, imx-bootlets and Barebox, including the specific patches and configurations for the Crystalfontz boards.
  • Then the kernel. The linux-cfa recipe uses the 3.10 based kernel available on github.
  • The machine configurations themselves, selecting Barebox as the bootloader and the correct kernel recipe. Also, these are choosing to install the kernel in the root filesystem instead of in its own partition.
  • Touchscreen calibration for the cfa-10057 and the cfa-10058 boards. This is required to get xinput-calibrator working properly as it can’t calibrate without starting values.

In a nut shell, you can now use the following commands to get a working image for your particular Crystalfontz board:

  • For your convenience, Freescale is providing a repo manifest to retrieve all the necessary git repositories. So first download and install repo:
    mkdir ~/bin
    curl > ~/bin/repo
    chmod a+x ~/bin/repo
  • We will work in a directory named fsl-community-bsp:
    mkdir fsl-community-bsp
    cd fsl-community-bsp
  • Ask repo to get the master branch, when Yocto 1.5 is released, you could select the new branch. (Edit: starting from September, 28th, you can use the branch named dora)
    repo init -u -b master
  • Download the layers:
    repo sync
  • Configure the build for cfa-10036:
    MACHINE=cfa10036 source ./setup-environment build
  • Start the build with:
    bitbake core-image-minimal
  • Grab a cup of coffee!

You’ll end up with an image that you can flash using the following command:
sudo dd if=tmp/deploy/images/cfa10036/core-image-minimal-cfa10036.sdcard of=/dev/mmcblk0

Obviously, you need to replace cfa10036 by the board model you are using in the above commands. While not completely perfect, core-image-sato is also working.

In detail, the contributions from Free Electrons are:

Contributions to Barebox: initial Marvell SoC support

Barebox is a bootloader that strives to be a modern alternative to U-Boot. It currently supports ARM, Blackfin, MIPS, NIOS2, OpenRISC, PowerPC and x86 as CPU architectures, and while it doesn’t have as much hardware support as U-Boot yet, it does have a number of very significant advantages over U-Boot: a proper device model very similar to the one used in the Linux kernel, which makes the code very clean and nice, and a configuration system that uses kconfig, like the Linux kernel, which is a lot better than the per-board header files used by U-Boot with lots of cryptic macros.

Free Electrons had already contributed to Barebox in the past, as our engineer Maxime Ripard added the support for the Crystalfontz i.MX28 boards.

More recently, we contributed basic support for the Marvell Kirkwood, Marvell Armada 370 and Marvell Armada XP ARM processors. This work was released as part of the 2013.07.0 release. For now, the support is fairly minimal, as it only allows to boot a Barebox bootloader that has serial port support. The most important part of the work was to write a kwbimage tool (see kwbimage.c), which allows to generate bootable images for Marvell processors. Our work contained minimal support for the Armada XP-based OpenBlocks AX3 board, the Armada XP-based GP development board, the Armada 370-based Mirabox from Globalscale and the Kirkwood-based Guruplug from Globalscale. Our work was quickly extended by Sebastian Hesselbarth, who added basic support for the Marvell Dove processor, and the Cubox platform from SolidRun, which uses the Dove processor.

Of course, such support is far from being complete, we are hoping in the future to add support for network, NAND and SD, in order to make Barebox really useful and usable on Marvell platforms.

The details of our contributions are:

Starting Linux directly from AT91bootstrap3

Here is an update for our previous article on booting linux directly from AT91bootstrap. On newer ATMEL platforms, you will have to use AT91bootstrap 3. It now has a convenient way to be configured to boot directly to Linux.

You can check it out from github:

git clone git://

That version of AT91bootstrap is using the same configuration mechanism as the Linux kernel. You will find default configurations, named in the form:

  • board_name can be: at91sam9260ek, at91sam9261ek, at91sam9263ek, at91sam9g10ek, at91sam9g20ek, at91sam9m10g45ek, at91sam9n12ek, at91sam9rlek, at91sam9x5ek, at91sam9xeek or at91sama5d3xek
  • storage can be:
    • df for DataFlash
    • nf for NAND flash
    • sd for SD card
  • our main interest will be in boot_strategy which can be:
    • uboot: start u-boot or any other bootloader
    • linux: boot Linux directly, passing a kernel command line
    • linux_dt: boot Linux directly, using a Device Tree
    • android: boot Linux directly, in an Android configuration

Let’s take for example the latest evaluation boards from ATMEL, the SAMA5D3x-EK. If you are booting from NAND flash:

make at91sama5d3xeknf_linux_dt_defconfig

You’ll end up with a file named at91sama5d3xek-nandflashboot-linux-dt-3.5.4.bin in the binaries/ folder. This is your first stage bootloader. It has the same storage layout as used in the u-boot strategy so you can flash it and it will work.

As a last note, I’ll had that less is not always faster. On our benchmarks, booting the SAMA5D31-EK using AT91bootstrap, then Barebox was faster than just using AT91bootstrap. The main reason is that barebox is actually enabling the caches and decompresses the kernel(see below, the kernel is also enaling the caches before decompressing itself) before booting.

Barebox 2011.03 released, with contributions from Free Electrons

BareboxBarebox is a bootloader started about two years ago for embedded systems of various architectures. It plays the same role as U-Boot, which is the best known project in this area, but has several advantages over U-Boot. First, it has a much better configuration and compilation system, based on the one used by the Linux kernel: instead of the rusty include/configs/myboard.h configuration headers in U-Boot, Barebox provides a nice menuconfig/xconfig/defconfig based configuration system, that everyone is familiar with. Second, Barebox has a source code organization very similar to the one of the Linux kernel and has replicated the device/driver model of the kernel. This allows to have a nice separation between device drivers and their instantiation, and a source code that looks familiar to anyone that already does kernel development.

Of course, as Barebox is newer than U-Boot, the number of architectures and platforms is more limited, but it is growing rapidly. It already supports ARM, PPC, Blackfin, x86 and a testing sandbox architecture. On ARM, the supported platforms are AT91, EP93xx, iMX, Nomadik, OMAP, S3C24xx and Versatile. On PPC, a single mpc5xxx platform is supported. Patches to add support for the NIOS architecture have also been posted recently (NIOS is a soft-core architecture from Altera).

As a young but fast-growing project, Barebox has chosen a quick development cycle: new releases are made each month, and Barebox 2011.03 has been released a few days ago. It has many ARM and generic improvements, but is also the first release with contributions from Free Electrons :

Gregory CLEMENT (3):
      BMP: Add support for 32bpp video frame buffer
      ARM STM/i.MX: Add possibility to choose the bit per pixel for STM video driver
      fb i.MX23/28: Add the reset control of LCD

My colleague Gregory Clement has contributed several improvements to framebuffer support on the i.MX platform. Those improvements were made in the context of a customer project, for which Barebox was used as a way of showing immediately after the device start-up a nice logo on the screen, while the system continues to boot in the background. Initially, the user had to wait 20+ seconds to see a logo on the screen showing that the system was booting. With our Barebox based solution, a logo is now visible on the screen less than 2 seconds after the power on button is pushed.