It's easy to compile images that can be run in qemu with buildroot. I don't know much about yocto, but you can use the crosstool-ng toolkit to compile a tool chain for cross compiling. You can have multiple tool chains, and have unique images for each of your respective targets, possibly just running your ocaml code locally and recompiling it for arm when you want to put it on the device :)

On Thu, Jun 25, 2015 at 11:04 PM, Berke Durak <berke.durak@gmail.com> wrote:

On Tue, Jun 23, 2015 at 6:32 AM, Markus Weißmann
<markus.weissmann@in.tum.de> wrote:
>
> I can offer experience in the following cases:
> 1) If your system is powerful enough (e.g. rasperry pi), you can just install the ocaml toolchain on your system and develop there on your target system.

Seconded.  We did almost that for one of our projects and it works
pretty well.  The difference is that we didn't use QEmu, but two of
our custom Q7 board (based on a Zynq ARM Cortex A9 with 512 MB RAM,
see http://xiphos.com/products/q7-processor/ ).

We use Yocto to generate two versions of a Linux system: the target
system, and a much larger version that contains developer tools (C
compiler, m4, etc.)  The development system runs from microSD cards,
and takes the better part of a gigabyte, while the target system has
to run from < 64 megs of flash.  The required run-time dependencies of
the target system have to be manually configured in the Yocto recipes.

We then manually install opam on the developer board, and use it to
compile our OCaml code. The generated native ARM executables are then
packaged into .ipks and transferred to the target Q7 board (connected
to actual hardware:
http://www.ghgsat.com/wp-content/uploads/2015/03/Payload-Selfie.jpg )
The packaging is done using a simple shell script that invokes ar and
tar.

We did try using QEmu but it's significantly slower, however it may
come into play as automating the build process (using a virtual
machine or dedicated hardware) is on our to do list, and build time
isn't as important when it's a nightly automated build.

Initially we looked into using a cross-compiler but we decided that
being able to use Opam largely outweighs any possible benefit we could
get from cross-compiling.  And cross-compiling is often a source of
headaches, even when compiling plain old C.  We would have to write a
lot of Yocto recipes to get it running.  Note that Yocto is written in
a progarmming language called Python and requires recipes to be
expressed mostly the same language.

To conclude, as powerful ARM systems are very cheap and plentiful
these days, and since the convenience of Opam is immense, I'm not sure
there is much incentive in using a cross-compiler.  BTW, is there a
maintained ARM cross-compiler?
--
Berke Durak

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