big / little endian

Joel Sherrill joel.sherrill at
Mon Apr 1 13:16:14 UTC 2002

Didier Ana wrote:
> Hi,
> We are working on a ARM7 cpu and porting RTEMS on.
> This might be an irrelevant question...  I wonder if the little or big
> endian bus mode could have any impact on the performance mainly on the
> tcp-ip stack side.
> Any idea on this ?

Since I haven't seen a response on this...

I am by no means an expert on this but I believe that "network neutral"
data format is big endian so  big endian CPU can avoid a bit of overhead
when building packets on the net.  I somehow suspect this isn't that
a factor as the x86 is little endian and shows great network performance
under RTEMS.  

By far the biggest win on any CPU is having optimized in_cksum support.
If RTEMS doesn't already have this for the ARM, then as soon as you
get far enough to have a stable network driver to test on, I would
recommend addressing that.

> Thanks,
> Didier Ana
> CXR sa
> Tel:  +33 (0) 237 628 806
> Mail: Didier.Ana at

Joel Sherrill, Ph.D.             Director of Research & Development
joel at                 On-Line Applications Research
Ask me about RTEMS: a free RTOS  Huntsville AL 35805
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