Is armv7em + FPv5-SP-D16-M supported?

[Andrei Ion]

Hei everyone,

I am trying to use the toolchain to build a specific configuration for FPU: -mfpu=fpv5-sp-d16. More exactly, I am trying to have single-precision.

According to documentation here, both single and double precision are included in v7E-M + FPv5-DP-D16-M.
Is this correct?

In the repo, I noticed that there is only one .cfg file for fpv5, omitting DP or SP (armv7em_hard_fpv5_d16.cfg).
Moreover, the runtime libs only support this version ./lib/clang-runtimes/armv7em_hard_fpv5_d16.

My questions would be:
Can armv7em_hard_fpv5_d16 libraries be used for both single and double precision? Can I use, for example, /lib/clang-runtimes/armv7em_hard_fpv5_d16/lib/libclang_rt.builtins-armv7em.a from this repo for -mfpu=fpv5-sp-d16?

Thank you! :)

[Michael Platings]

Hi Andrei,

If -mfpu=fpv5-sp-d16 is the configuration you want then armv7em_hard_fpv5_d16 would not be appropriate because it needs double-precision floating point hardware.

According to the documentation you linked to, the Cortex-M7 is available in three configurations, which may or may not include single or double-precision floating point hardware.

For LLVM Embedded Toolchain for Arm 16 and later you don't have to choose a config file. Instead the multilib system will choose a suitable library based on your flags. See https://github.com/ARM-software/LLVM-embedded-toolchain-for-Arm/tree/llvm-16#experimental-multilib.

For -mfpu=fpv5-sp-d16 it looks like the multilib system would choose the armv7em_hard_fpv4_sp_d16 library, which I think is the best choice for you out of the available options.

[Andrei Ion]

Hei Michael,

Thank you for a prompt reply!

I will give it a try with fpv4.
According to this page as well, there doesn't seem to be much difference between fpv4 and fpv5 that I should care about :)