Crystalfontz boards support in Yocto

The Yocto 1.5 release is approaching and the Freescale layer trees are now frozen.
Bootlin 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  • Support for a newer version of the Barebox mainline, 2013.08.0.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 https://dl-ssl.google.com/dl/googlesource/git-repo/repo > ~/bin/repo
    chmod a+x ~/bin/repo
    PATH=${PATH}:~/bin
  • 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 https://github.com/Freescale/fsl-community-bsp-platform -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 Bootlin 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://github.com/linux4sam/at91bootstrap.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><storage>_<boot_strategy>_defconfig

  • 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
make

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.