compiling for nrf5340 FPU

RE: compiling for nrf5340 FPU

Revilo — Fri, 19 Jul 2024 12:25:12 GMT

In our project we are using a nRF52 with FPU, and I was assuming that the FPU is used by default. We are in the middle of the project and are doing quite some (single, no double) float operations.

I just added CONFIG_FPU=y and the memory footprint is now higher (flash +7k, RAM +1k). Shouldn't the code need less memory since the hardware FPU is used to compute the calculations? What could cause such behaviour?

EDIT: one section of float operations takes always 62us with CONFIG_FPU=y and 92..122us without. It's a very corase measurement with 31.5us per tick, but the FPU seems to be used.

kind regards

RE: compiling for nrf5340 FPU

BitWiggler2000 — Thu, 26 Jan 2023 16:09:23 GMT

Thank you for the quick reply! I was so focused on the unknowns I forgot to check the basics. It says right there in the data brief, "Single-precision floating-point unit (FPU)"....

Fixing this, the runtime went down to under a second. Very nice.

RE: compiling for nrf5340 FPU

Vidar Berg — Thu, 26 Jan 2023 12:07:24 GMT

Hello,

CONFIG_FPU=y should be sufficient to enable the floating point unit. And CONFIG_FPU_SHARING=y if you are doing float operations across multiple threads.

Please try to use the suffix 'f' when using hardcoded values to inform the compiler it should be a float type and not a double. This did the trick when I tested your code here.

Best regards,

Vidar

Edit: the __aeabi_f2d function will convert a float input to a double. As only single precision floats is supported in HW, it makes sense that this conversion is done in SW.

RE: compiling for nrf5340 FPU

BitWiggler2000 — Wed, 25 Jan 2023 23:05:39 GMT

Here's the make options again delimited

arm-zephyr-eabi-gcc.exe
-DKERNEL
-DMBEDTLS_CONFIG_FILE=\"nrf-config.h\"
-DMBEDTLS_USER_CONFIG_FILE=\"nrf-config-user.h\"
-DNRF5340_XXAA_APPLICATION
-DNRF_SKIP_FICR_NS_COPY_TO_RAM
-DNRF_TRUSTZONE_NONSECURE
-DTFM_PSA_API
-DUSE_PARTITION_MANAGER=1
-D__PROGRAM_START
-D__ZEPHYR__=1
-I../../../bsp_nrf5340
-I../../../common
-IC:/ncs/v2.2.0/zephyr/include
-Izephyr/include/generated
-IC:/ncs/v2.2.0/zephyr/soc/arm/nordic_nrf/nrf53
-IC:/ncs/v2.2.0/zephyr/soc/arm/nordic_nrf/common/.
-IC:/ncs/v2.2.0/nrf/include
-IC:/ncs/v2.2.0/nrf/include/tfm
-IC:/ncs/v2.2.0/nrf/tests/include
-Itfm/generated/interface/include
-IC:/ncs/v2.2.0/modules/hal/cmsis/CMSIS/Core/Include
-IC:/ncs/v2.2.0/modules/hal/nordic/nrfx
-IC:/ncs/v2.2.0/modules/hal/nordic/nrfx/drivers/include
-IC:/ncs/v2.2.0/modules/hal/nordic/nrfx/mdk
-IC:/ncs/v2.2.0/zephyr/modules/hal_nordic/nrfx/.
-Itfm/install/interface/include
-Imodules/nrfxlib/nrfxlib/nrf_security/src/include/generated
-IC:/ncs/v2.2.0/nrfxlib/nrf_security/include
-IC:/ncs/v2.2.0/nrfxlib/nrf_security/include/mbedtls
-IC:/ncs/v2.2.0/mbedtls/include
-IC:/ncs/v2.2.0/mbedtls/include/mbedtls
-IC:/ncs/v2.2.0/mbedtls/include/psa
-IC:/ncs/v2.2.0/mbedtls/library
-IC:/ncs/v2.2.0/nrfxlib/crypto/nrf_oberon/include/mbedtls
-IC:/ncs/v2.2.0/nrfxlib/crypto/nrf_oberon/include
-isystem C:/ncs/v2.2.0/zephyr/lib/libc/minimal/include
-isystem c:/ncs/toolchains/v2.2.0/opt/zephyr-sdk/arm-zephyr-eabi/bin/../lib/gcc/arm-zephyr-eabi/12.1.0/include
-isystem c:/ncs/toolchains/v2.2.0/opt/zephyr-sdk/arm-zephyr-eabi/bin/../lib/gcc/arm-zephyr-eabi/12.1.0/include-fixed
-Wall
-Werror
-Wextra
-fno-strict-aliasing
-Og
-imacros C:/github/squawk-demo/vocoder/apps/007_mem/build/zephyr/include/generated/autoconf.h
-ffreestanding
-fno-common
-g
-gdwarf-4
-fdiagnostics-color=always
-mcpu=cortex-m33
-mthumb
-mabi=aapcs
-mfpu=fpv5-sp-d16
-mfloat-abi=hard
-mfp16-format=ieee
--sysroot=C:/ncs/toolchains/v2.2.0/opt/zephyr-sdk/arm-zephyr-eabi/arm-zephyr-eabi
-imacros C:/ncs/v2.2.0/zephyr/include/zephyr/toolchain/zephyr_stdint.h
-Wformat
-Wformat-security
-Wno-format-zero-length
-Wno-main
-Wno-pointer-sign
-Wpointer-arith
-Wexpansion-to-defined
-Wno-unused-but-set-variable
-Werror=implicit-int
-fno-pic
-fno-pie
-fno-asynchronous-unwind-tables
-fno-reorder-functions
--param=min-pagesize=0
-fno-defer-pop
-fmacro-prefix-map=C:/github/squawk-demo/vocoder/apps/007_mem=CMAKE_SOURCE_DIR
-fmacro-prefix-map=C:/ncs/v2.2.0/zephyr=ZEPHYR_BASE
-fmacro-prefix-map=C:/ncs/v2.2.0=WEST_TOPDIR
-ffunction-sections
-fdata-sections
-std=c99
-nostdinc
-MD
-MT CMakeFiles/app.dir/src/console_cmds.c.obj
-MF CMakeFiles\app.dir\src\console_cmds.c.obj.d
-o CMakeFiles/app.dir/src/console_cmds.c.obj
-c ../src/console_cmds.c