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Vivek Sankaranarayanan
Vivek Sankaranarayanan
Associate II
August 17, 2017
Solved

Floating point instructions

  • August 17, 2017
  • 10 replies
  • 3711 views
Posted on August 17, 2017 at 15:16

I am using STM32F303VC with System Workbench IDE.

I can't for the life of me get the hard floating point option to work. The compiler never generates floating point instructions. It' only generating soft code with library calls. Anyone knows what the problem could be?

    This topic has been closed for replies.
    Best answer by RomainR.
    Posted on August 17, 2017 at 20:36

    What is your SW4STM32 version ?

    Maybe upgrade to latest version should be fix your issue.

    Best regards

    10 replies

    Tesla DeLorean
    Tesla DeLorean
    Guru
    August 17, 2017
    Posted on August 17, 2017 at 17:01

    >>Anyone knows what the problem could be?

    Settings and defines sent to the compiler? Not hard to get GNU/GCC to compile FPU instructions.

    The FPU only supports 32-bit floats, not doubles.

    1.23 is a double, 1.23f is a float

    printf/scanf use doubles

    The FPU only supports simple arithmetic functions, anything complex or transcendental will use mix of software/hardware.

    Most stuff tends to use the Soft ABI, though that might be changing now the M7 and M4F are getting more prevalent.

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    Vivek Sankaranarayanan
    Vivek SankaranarayananAuthor
    Associate II
    August 17, 2017
    Posted on August 17, 2017 at 19:46

    The FPU only supports 32-bit floats, not doubles.

    1.23 is a double, 1.23f is a float

    printf/scanf use doubles

    The FPU only supports simple arithmetic functions, anything complex or transcendental will use mix of software/hardware.

    Most stuff tends to use the Soft ABI, though that might be changing now the M7 and M4F are getting more prevalent.

    So i have a simple statement saying:

    float x; x = 1.25; x = x*x;

    x = 1.25; x = x*x;

    x = x*x;

    Going through the dissasembly I don't see a single floating point instruction. Even if it were double, the compiler must be making use of 32bit floating point hardware to do double right?

    Tesla DeLorean
    Tesla DeLorean
    Guru
    August 17, 2017
    Posted on August 17, 2017 at 21:32

    The optimizer should flatten that to constants.

    This was one of my test cases, built with GNU/GCC 4.9.3

    float test1(float x, float y)

    {

      return(x + y + sqrtf((x * x) + (y * y)));

    }

    demo.lss listing

    ...

    08002578 <test1>:

    //******************************************************************************

    ♯ include <math.h>

    float test1(float x, float y)

    {

     8002578:    b508          push    {r3, lr}

     800257a:    ed2d 8b02     vpush    {d8}

     800257e:    eeb0 8a40     vmov.f32    s16, s0

      return(x + y + sqrtf((x * x) + (y * y)));

     8002582:    ee20 0aa0     vmul.f32    s0, s1, s1

    //******************************************************************************

    ♯ include <math.h>

    float test1(float x, float y)

    {

     8002586:    eef0 8a60     vmov.f32    s17, s1

      return(x + y + sqrtf((x * x) + (y * y)));

     800258a:    eea8 0a08     vfma.f32    s0, s16, s16

     800258e:    f001 fcd9     bl    8003f44 <sqrtf>

     8002592:    ee38 8a28     vadd.f32    s16, s16, s17

    }

     8002596:    ee38 0a00     vadd.f32    s0, s16, s0

     800259a:    ecbd 8b02     vpop    {d8}

     800259e:    bd08          pop    {r3, pc}

    Compiling file: main.c

    arm-none-eabi-gcc -c -mcpu=cortex-m4 -mthumb -mfloat-abi=hard -mfpu=fpv4-sp-d16

    -Os -ffunction-sections -fdata-sections -Wall -Wstrict-prototypes -Wextra -std=gnu89

    -g -ggdb3 -fverbose-asm -Wa,-ahlms=out/main.lst  -DUSE_STDPERIPH_DRIVER 

    -DSTM32F4XX  -DUSE_STM32F4_DISCOVERY  -DUSE_USB_OTG_FS  -DHSE_VALUE=8000000 

    -D__FPU_PRESENT=1 -MD -MP -MF out/main.d -I.  -Iinc main.c -o out/main.o

    Linking target: out/demo.elf

    arm-none-eabi-g++ -mcpu=cortex-m4 -mthumb -mfloat-abi=hard -mfpu=fpv4-sp-d16

    -Tstm32f4xx.ld -g -Wl,-Map=out/demo.map,--cref,--no-warn-mismatch -Wl,--gc-sections

    -nostartfiles  out/startup_stm32f4xx.o out/diskio.o out/ff.o out/main.o out/misc.o

    out/newlib_stubs.o out/stm32f4_discovery.o out/stm32f4_discovery_sdio_sd.o

    out/stm32f4xx_dma.o out/stm32f4xx_gpio.o out/stm32f4xx_rcc.o out/stm32f4xx_sdio.o

    out/stm32fxxx_it.o out/system_stm32f4xx.o    -o out/demo.elf
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    RomainR.
    RomainR.
    ST Employee
    August 17, 2017
    Posted on August 17, 2017 at 17:12

    Hi,

    Can you check the configuration of your project this way:

    Into 

    System Workbench Project \ Properties \ C/C++ Build \ Settings \ Tool Settings \ Preprocessor

    Check if __FPU_PRESENT and __FPU_USED symbols are defined

    0690X00000607waQAA.png

    And then into MCU Settings Floating Point ABI is hard

    0690X00000607rmQAA.png

    Best regards

    To give better visibility on the answered topics, please click on Accept as Solution on the reply which solved your issue or answered your question.
    Vivek Sankaranarayanan
    Vivek SankaranarayananAuthor
    Associate II
    August 17, 2017
    Posted on August 17, 2017 at 19:42

    I have both those symbols defined in the preprocessor.

    But my problem could be this. I cannot select anything under Float Point Hardware. I have only No unit listed.

    0690X00000607wqQAA.png

    Could this be the problem?

    RomainR.
    RomainR.Best answer
    ST Employee
    August 17, 2017
    Posted on August 17, 2017 at 20:36

    What is your SW4STM32 version ?

    Maybe upgrade to latest version should be fix your issue.

    Best regards

    To give better visibility on the answered topics, please click on Accept as Solution on the reply which solved your issue or answered your question.
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