[yocto] How do I used Yocto to build an sdcard image for my Raspberry Pi 3 Model B?

[Thomas A. F. Thorne MEng AUS MIET]

I was starting to look at using Yocto <https://www.yoctoproject.org/> as
a system for building software images for the Raspberry Pi 3 Model B
that I have. I wanted to try using Yocto as there are some projects at
my office that may begin using it in the future. One of the nice points
is that all the setup of cross compilers for your target system is
handled by a Yocto layer. There is already a Yocto layer for the
Raspberry Pi
<http://git.yoctoproject.org/cgit/cgit.cgi/meta-raspberrypi/>(meta-raspberrypi
<http://git.yoctoproject.org/cgit/cgit.cgi/meta-raspberrypi/>) and a
custom meta-rpi <https://github.com/jumpnow/meta-rpi> layer someone has
put together with a few more example images.

I need to either cross-compile kernel modules or use Yocto as I have
special drivers I wish to add to the Pi. These are already compiled and
working on my Ubuntu PC and I hoped using Yocto might make it easy to
cross compile these and any other updates in the future.

My difficulty is that the SD Card image talked about in
the meta-raspberrypi documentation
<http://git.yoctoproject.org/cgit/cgit.cgi/meta-raspberrypi/about/> and
several tutorials, never gets generated, even on successful builds.


    Tutorials Mentioning The Use Of |dd| & An .sdimg File

  * Build a Raspberry Pi 2 Minimal Image with The Yocto Project
    <http://www.cnx-software.com/2015/02/27/yocto-project-raspberry-pi-2-board-minimal-image/>
  * Building Raspberry Pi Systems with Yocto
    <http://www.jumpnowtek.com/rpi/Raspberry-Pi-Systems-with-Yocto.html>
  * 12MB Minimal Image for Raspberry Pi using the Yocto Project
    <http://www.cnx-software.com/2013/07/05/12mb-minimal-image-for-raspberry-pi-using-the-yocto-project/>
  * Poky Raspberry Pi SD Card Image
    <http://www.crashcourse.ca/wiki/index.php/Poky_Raspberry_Pi_SD_Card_Image>


    Commonly Seen Error

None of the builds I have made so far generate .sdimg files. When I try
to add the |sdcard| or |sdcard_image-rpi| image types to IMAGE_FSTYPES I
get messages such as:

|ERROR:
/home/thomasthorne/work/yocto-rpi/meta-raspberrypi/recipes-core/images/rpi-test-image.bb:
No IMAGE_CMD defined for IMAGE_FSTYPES entry 'sdcard_image-rpi' -
possibly invalid type name or missing support class |


    Main Questions

/How do I generate the SD card image for my Pi from Yocto?/

Do I need to format the SD card manually and copy over the contents bit
by bit?

Why do all these tutorials suggest it would be as simple as a
single |dd| command? I guess something changed in the last couple of
years and they are all out of date.


This was also posted at
http://raspberrypi.stackexchange.com/questions/57155/how-do-i-used-yocto-to-build-an-sdcard-image-for-my-raspberry-pi-3-model-b
before I realised it is probably more of a Yocto question than a
Raspberry Pi one. 

I will be very grateful of any help or advice you can offer.  Even an
explanation of when the generation of SD card images was dropped from
the Yocto Project would be very helpful. 

Regards,

-- 
Thomas A. F. Thorne MEng. AUS MIET
*Software Engineer*

*NET2EDGE*

Tel: +44 3450 130 030 <tel:+443450130030>
Email: Thomas.Thorne at Net2Edge.com <mailto:Thomas.Thorne at Net2Edge.com>
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