RTOS/AM3358: IEEE 754 floating point support

Alexander Frick

Intellectual 645 points

Part Number: AM3358

Tool/software: TI-RTOS

I am in need of hardware floating point that is fully implement the IEEE 754 standard for floating-point arithmetic.

All I can find is that the 3358 supports NEON but that won't work for me.

What is my best option besides NEON?

More specifically, looking at https://gcc.gnu.org/onlinedocs/gcc-4.8.3/gcc/ARM-Options.html , what is supported on the AM3358:

‘vfp’, ‘vfpv3’, ‘vfpv3-fp16’, ‘vfpv3-d16’, ‘vfpv3-d16-fp16’, ‘vfpv3xd’, ‘vfpv3xd-fp16’

I think would want vfpv3 to be fully compliant with IEEE 754 per:

http://processors.wiki.ti.com/index.php/Cortex-A8#Neon_and_VFP_both_support_floating_point.2C_which_should_I_use.3F

But I figured I would ask.

Thanks!

over 8 years ago

0 Rahul Prabhu over 8 years ago

TI__Guru** 116950 points

Alex,

For floating point operation, we usually recommend user to check out the following link for using ARM floating point features using GCC compiler settings as this describes the options in greater detail:
embeddedartistry.com/.../r1q7pksku2q3gww9rpqef0dnskphtc

Based on that article, you will need to set the -mfloat-abi flag and -mfpu based on the project requirements.

Regards,
Rahul

0 Alexander Frick over 8 years ago in reply to Rahul Prabhu

Intellectual 645 points

Thanks for the great link Rahul!

Looking at the snippet from the link below about NEON would make me think that if I use 'neon-fp-armv8', I am IEEE 754 compliant. Correct?

"Prior to ARMv8, the ARM architecture distinguished between VFP and NEON floating-point support. NEON was not fully IEEE 754 compliant, and there were instructions that VFP supported which NEON did not. These issues have been resolved with ARMv8."

0 Rahul Prabhu over 8 years ago in reply to Alexander Frick

TI__Guru** 116950 points

Alex,

Please note AM335x has Cortex A8 which is armv7 architecture so, I don`t think option "neon-fp-armv8" can be used in your project.

Looking at the ARM technical reference manual, it appears only using VFP co-processor options will generate floating point code that is IEEE-754 compliant. This is the part of the ARM technical reference manual that I am referring to :
infocenter.arm.com/.../index.jsp

Given this information, I think you need to use VFP without NEON enabled which should be option VFPv3. Comparison of VFPv3 vs NEON is provided in a wiki link here:
processors.wiki.ti.com/.../Using_NEON_and_VFPv3_on_Cortex-A8

Regards,
Rahul

0 Alexander Frick over 8 years ago in reply to Rahul Prabhu

Intellectual 645 points

Thank you for the detailed response Rahul!

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RTOS/AM3358: IEEE 754 floating point support