Philippe Gerum wrote:
On Fri, 2006-12-01 at 18:22 +0100, Jan Kiszka wrote:
Wolfgang Grandegger wrote:
Jan Kiszka wrote:
Hi,

the new Xenomai example repository has been created. I don't want to
repeat here what is explained already on the related wiki page, please
have a look at

    http://www.xenomai.org/index.php/Examples

Instead, let me sketch what could be done next:

 o Port existing examples, snippets, demos from ksrc/skins/* over, make
   them compilable and runnable if required.

 o Identify what kind of examples are lacking. You, the user, is needed
   here. What do *you* think is missing, what would be helpful to show?

 o Check what is needed to compile kernel-based examples over PPC 2.4.
   Philippe indicated that some switches are likely missing (x86 is fine
   already, other archs are 2.6-only).
Some time ago I sent a patch for RTnet using the "kernel CFLAGS
capturing" trick to get proper switches for 2.4:

http://sourceforge.net/mailarchive/forum.php?thread_id=9493711&forum_id=24610


We could do the same trick here.
Yeah, I had a look at this before. The point is that I would prefer to
keep things _simple_ and self-contained. This capturing requires some
helper Makefile and complex call nestings that likely only people with
advanced make and shell skills can understand and adopt to their projects.

I tend to agree on the "keep it simple" mantra, but still, there are at
least two other aspects which are quite important too:

- Nobody should expect to be able to develop a complete project only
relying on paste-and-copy of example code. Since we are specifically
talking about Makefile rules, we could not provide any set that would
match everyone's project anyway, with respect to software and hardware
requirements. Therefore, at some point, people really need to know what
they are doing, which means that they should also know how to properly
build out-of-tree modules with _their_ own 2.4 setup (well, if any
"proper" solution exists, that is). And basically, I do hope that nobody
starts implementing kernel modules without having - at least - a vague
idea, about how to compile them for its platform in the first place...

- Given that there is life beyond x86, we need to make sure that all
Xenomai ports are considered equal, at least with respect to generic
issues. Whilst it's ok to provide a x86-only 2.4 Makefile for compiling
a x86-centric example, it's not for anything which could demonstrate a
feature on any platform.

This said, I agree that adding a fake module directory to capture the
flags set by the main kernel Makefile is one step beyond ugliness; the
other approach being to only provide a 2.6 Makefile frag. As 2007
approaches, I think that anyone still involved with projects relying on
2.4 kernels do know how to build 2.4 modules for the targeted platform.

I think the example modules should compile on any platform and the "kernel CFLAGS capturing" trick is the most straight-forward way to do it for 2.4. It simplifies our life, avoids fiddling with various arch dependent flags in the Makefile, which will be even more ugly, and it serves as an example on how to get proper flags. Therefore I tend to add an appropriate script to the "scripts" subdirectory.

But maybe things are that complicated already, and this is just
different complexity. How do you compile simple out-of-tree modules
against 2.4 PPC kernels? Are there any standard flags? Or is it
different for each board or each compiler version or whatever?

Jan

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