[Buildroot] endian issue

Marcel korgull at home.nl
Sat May 15 15:26:57 UTC 2010

On Saturday 15 May 2010 04:43:29 pm Grant Edwards wrote:
> On 2010-05-15, Lionel Landwerlin <llandwerlin at gmail.com> wrote:
> > Le samedi 15 mai 2010 ?? 15:47 +0200, Marcel a ??crit :
> >> I'm using an Atmel sam9g45 using buildroot with linux 2.6.33.
> >> 
> >> I currently have most of my things working but run into an issue which
> >> is endian related.
> > 
> > The endianness configuration of your processor isn't something you
> > can usually change 'on-the-fly'. It's usually set up early in the
> > boot process.
> While the endian configuration of the ARM9 core can be changed, the
> AT91 peripherals are little-endian.  In theory, he should be able to
> run the ARM9 core in big-endian mode, but a running uC core without
> any working peripherals is surprisingly useless.
> > So you have to choose whether you want to compile all your system in
> > big or little endian, you can select that from the buildroot
> > architecture configuration (arm -> little, armeb -> big, for
> > example).
> In this case, he has to choose little-endian.

That's very clear. 

> [I've never seen an ARM-based uController that had peripherals with
> configurable endianess -- are there any?]
> >> Is there any way to compile my package in big-endian mode from
> >> buildroot? Or is there another way I should force this?
> > 
> > You can't select that for 1 package, it's for the whole system or
> > nothing. Otherwise, the smartest approch would be to make endian
> > detection (at compile time or at running time) to adapt your
> > processing algorithm.
> Yep, the OP's should driver should return data in host-order.
> Otherwise, he'll have to suffer the guilt of knowing that a few years
> from now some poor sod who inherits the code will have a stroke from
> the effort required to resist the urge to track down the OP and slap
> him silly.

If I wish to do that, how do I detect the endianness of a sytem and do I need 
to reformat my data in my drivers for this ? If so, isn't that a pure waste of 
cpu cycles for the sake of reusable code ?
If I can do this without any speed sacrifice than I will do it, if not....than 
it's simply not an option for this system.

Best regards,

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