[Buildroot] [PATCH] configs: nitrogen*: enable NEON support
Thomas Petazzoni
thomas.petazzoni at free-electrons.com
Fri Sep 16 16:26:50 UTC 2016
Hello,
On Fri, 16 Sep 2016 16:20:42 +0200, Gary Bisson wrote:
> Because the first two configurations are for i.MX6 (ARM Cortex-A9)
> whereas the last one is i.MX7 (ARM Cortex-A7).
>
> So relying on Config.in.arm, the Cortex-A9 doesn't have VFPv4:
> https://git.buildroot.net/buildroot/tree/arch/Config.in.arm#n125
> https://git.buildroot.net/buildroot/tree/arch/Config.in.arm#n141
OK, then you should be using the VFPv3 instead of the NEON for FPU.
Indeed:
"""
If the selected floating-point hardware includes the NEON extension
(e.g. '-mfpu'='neon'), note that floating-point operations are not
generated by GCC's auto-vectorization pass unless
'-funsafe-math-optimizations' is also specified. This is because
NEON hardware does not fully implement the IEEE 754 standard for
floating-point arithmetic (in particular denormal values are
treated as zero), so the use of NEON instructions may lead to a
loss of precision.
"""
Thomas
--
Thomas Petazzoni, CTO, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com
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