Re: [Discuss-gnuradio] ZedBoard GNU Radio image boot problems

[West, Nathan]

On Thu, Sep 4, 2014 at 9:49 AM, Tom Rondeau <address@hidden> wrote:
>
> On Wed, Sep 3, 2014 at 5:53 PM, Philip Balister <address@hidden> wrote:
>>
>>
>>
>> On 09/03/2014 04:30 PM, Nowlan, Sean wrote:
>> > I'm trying to boot a ZedBoard with the GNU Radio image here:
>> > http://gnuradio.org/data/sdk/zedboard_armv7a-hf-vfp-neon/. I picked the 
>> > hard
>> > float image even though the tutorial points to the soft float image
>> > (http://gnuradio.org/redmine/projects/gnuradio/wiki/Zynq). I don't know why
>> > I'd want the soft float image since using the FPU will be much faster.
>> >
>>
>> Hard float isn't that much faster. It referes to the ARM abi used for
>> function calls. Hard float lets you return floats in NEON registers,
>> which makes functions that return floats faster. Pretty much everything
>> else is the same. So, it is a win, but not huge, except for certain cases.
>>
>> Philip
>
>
> Nathan and I have both done some tests. You can get a few percent
> improvement in speed with just hard float. That by itself was not a
> compelling enough reason to drop the ORC support. It was only because of the
> NEON VOLK proto-kernels that made the change worth it.
>
> I had some data that I was going to publish at one point, but it was too
> confused with different development stages so that the comparisons wouldn't
> be clean or clear.
>
> Tom
>
>

That's correct, in my VOLK tests the only time hardfloat made any
difference was when the compiler inserted a call to its runtime
library for generic code. I expect this will come up in the VOLK
and/or embedded working group sessions at grcon.