[Buildroot] [PATCH 10/16] arch/arm: add support for hard-float on Cortex-M4
Arnout Vandecappelle
arnout at mind.be
Wed Mar 16 23:45:19 UTC 2016
On 03/16/16 22:43, Thomas Petazzoni wrote:
> Cortex-M4 cores can optionally have a FPv4-SP floating point unit
> (which is different than the VFPv4). This commit adds the necessary
> Config.in options to allow the user to enable the use of this FPU, and
> to build an EABIhf toolchain for Cortex-M4.
>
> Note that for now the kernel does not have CONFIG_VFP support for
> ARMv7-M, so in practice, this VFP support cannot really be used for
> the moment.
As in, when you select this option, then your target will fail dramatically
because it's hardfloat so even a simple printf will crash violently if a
reschedule happens in the middle?
If so, I'm not so sure we really want this option...
>
> Signed-off-by: Thomas Petazzoni <thomas.petazzoni at free-electrons.com>
> ---
> arch/Config.in.arm | 23 +++++++++++++++++++++--
> 1 file changed, 21 insertions(+), 2 deletions(-)
>
> diff --git a/arch/Config.in.arm b/arch/Config.in.arm
> index ee612f5..ad3c725 100644
> --- a/arch/Config.in.arm
> +++ b/arch/Config.in.arm
> @@ -31,6 +31,12 @@ config BR2_ARM_CPU_HAS_VFPV4
> bool
> select BR2_ARM_CPU_HAS_VFPV3
>
> +config BR2_ARM_CPU_MAYBE_HAS_FPV4_SP
Since the gcc option has -d16, shouldn't we have that as well?
> + bool
> +
> +config BR2_ARM_CPU_HAS_FPV4_SP
> + bool
> +
> config BR2_ARM_CPU_HAS_ARM
> bool
>
> @@ -177,6 +183,7 @@ config BR2_cortex_m3
> config BR2_cortex_m4
> bool "cortex-M4"
> select BR2_ARM_CPU_HAS_THUMB2
> + select BR2_ARM_CPU_MAYBE_HAS_FPV4_SP
> select BR2_ARM_CPU_ARMV7M
> config BR2_fa526
> bool "fa526/626"
> @@ -218,10 +225,11 @@ config BR2_ARM_ENABLE_NEON
>
> config BR2_ARM_ENABLE_VFP
> bool "Enable VFP extension support"
As I understand it (but I could be wrong), FPv4 is not again different from
VFP, i.e. it's again a different ABI (like softfloat and VFP are different
ABIs). At least, you get different flags in the ELF files. So I would tend to
really make a separate option for FPv4, to avoid all confusion. That is,
assuming that I'm right about it being a different ABI.
Note that in practice it doesn't make much of a difference becaus you never
have both VFP and FPv4 on the same processor. Well, at least for the time being
- who knows what kind of ugliness ARM will still invent :-)
Regards,
Arnout
> - depends on BR2_ARM_CPU_MAYBE_HAS_VFPV2
> + depends on BR2_ARM_CPU_MAYBE_HAS_VFPV2 || BR2_ARM_CPU_MAYBE_HAS_FPV4_SP
> select BR2_ARM_CPU_HAS_VFPV4 if BR2_ARM_CPU_MAYBE_HAS_VFPV4
> select BR2_ARM_CPU_HAS_VFPV3 if BR2_ARM_CPU_MAYBE_HAS_VFPV3
> select BR2_ARM_CPU_HAS_VFPV2 if BR2_ARM_CPU_MAYBE_HAS_VFPV2
> + select BR2_ARM_CPU_HAS_FPV4_SP if BR2_ARM_CPU_MAYBE_HAS_FPV4_SP
> help
> For some CPU cores, the VFP extension is optional. Select
> this option if you are certain your particular
> @@ -264,7 +272,7 @@ config BR2_ARM_EABI
>
> config BR2_ARM_EABIHF
> bool "EABIhf"
> - depends on BR2_ARM_CPU_HAS_VFPV2
> + depends on BR2_ARM_CPU_HAS_VFPV2 || BR2_ARM_CPU_HAS_FPV4_SP
> help
> The EABIhf is an extension of EABI which supports the 'hard'
> floating point model. This model uses the floating point
> @@ -285,6 +293,7 @@ endchoice
> choice
> prompt "Floating point strategy"
> depends on BR2_ARM_EABI || BR2_ARM_EABIHF
> + default BR2_ARM_FPU_FPV4_SP if BR2_ARM_CPU_HAS_FPV4_SP
> default BR2_ARM_FPU_VFPV4D16 if BR2_ARM_CPU_HAS_VFPV4
> default BR2_ARM_FPU_VFPV3D16 if BR2_ARM_CPU_HAS_VFPV3
> default BR2_ARM_FPU_VFPV2 if BR2_ARM_CPU_HAS_VFPV2
> @@ -374,6 +383,15 @@ config BR2_ARM_FPU_VFPV4D16
> cores, including the earlier Cortex-A{8, 9}, you should
> instead select VFPv3-D16.
>
> +config BR2_ARM_FPU_FPV4_SP
> + bool "FPv4-SP-D16"
> + depends on BR2_ARM_CPU_HAS_FPV4_SP
> + help
> + This option allows to use the FPv4-SP floating point unit,
> + as available in some ARMv7-M processors (Cortex-M4). This
> + option requires a FPv4-SP unit that has 16 double-precision
> + registers.
> +
> config BR2_ARM_FPU_NEON
> bool "NEON"
> depends on BR2_ARM_CPU_HAS_NEON
> @@ -475,6 +493,7 @@ config BR2_GCC_TARGET_FPU
> default "vfpv3-d16" if BR2_ARM_FPU_VFPV3D16
> default "vfpv4" if BR2_ARM_FPU_VFPV4
> default "vfpv4-d16" if BR2_ARM_FPU_VFPV4D16
> + default "fpv4-sp-d16" if BR2_ARM_FPU_FPV4_SP
> default "neon" if BR2_ARM_FPU_NEON
> default "neon-vfpv4" if BR2_ARM_FPU_NEON_VFPV4
>
>
--
Arnout Vandecappelle arnout at mind be
Senior Embedded Software Architect +32-16-286500
Essensium/Mind http://www.mind.be
G.Geenslaan 9, 3001 Leuven, Belgium BE 872 984 063 RPR Leuven
LinkedIn profile: http://www.linkedin.com/in/arnoutvandecappelle
GPG fingerprint: 7493 020B C7E3 8618 8DEC 222C 82EB F404 F9AC 0DDF
More information about the buildroot
mailing list