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    • sprinf conversion of float is not working for STM32F7

    Posted by Breinholm on 2016-02-16 10:33

    I'm tryint to use sprintf to convert a float to a string, but the returned string is empty (just the '\0' is returned).
    Do any of you know of a trick that can make it work?

    I'm using the latest versions of AC6 and the "Hello World" example from cube.

    /Breinholm

    Reads: 57872
    Posted by tarek bouchkati on 2016-02-16 10:58 Tunisia

    Hello Breinholm,

    Check your linker flags (project properties > C/C++ Build > Setings > Tool Settings (TAB) > MCU GCC Linker > Miscellaneous > Linker flags),
    if you are using nanolib "-specs=nano.specs" you need to add "-u _printf_float" to enable float printf.

    Best Regards,
    TarekB

         Posted by sync1 on 2016-06-19 13:47

    Hi Tarek,

    I treid adding "-u _printf_float" to enable float printf. as you suggest but after build i get the following errors?


    Building target: EM34.elf
    Invoking: MCU GCC Linker
    arm-none-eabi-gcc -mcpu=cortex-m3 -mthumb -mfloat-abi=soft -specs=nosys.specs -specs=nano.specs -Xlinker -u _printf_float -T"../STM32F103CBTx_FLASH.ld" -Wl,-Map=output.map -Wl,--gc-sections -lm -o "EM34.elf" @"objects.list"
    arm-none-eabi-gcc.exe: error: _printf_float: No such file or directory
    make: *** EM34.elf Error 1

    I am using latest updates for STM32 CubeMX, and STM32 Workbench..... I recall this solution used to work on previuos version but not now?
    Any suggestions?

         Posted by tang on 2016-06-20 11:13

    Hi,

    I think you put the "-u _printf_float" on the wrong place, it should be in the linker flags and not the -Xlinker area.

    Regards
    Kevin.

         Posted by sync1 on 2016-06-20 12:19

    Hi Tang,

    I am sure I put the options under the Linker Flags, as I said this option was working under previous versions (unsure which version it was) but I recently clicked "update" on both the STM32 CubeMX and the System32 Workbench programs and now for some unlknown reason The Linker throws the following errors:

    Building target: EM34.elf
    Invoking: MCU GCC Linker
    arm-none-eabi-gcc -mcpu=cortex-m3 -mthumb -mfloat-abi=soft -specs=nosys.specs -specs=nano.specs -Xlinker -u _sprintf_float -Xlinker -u _printf_float -T"../STM32F103CBTx_FLASH.ld" -Wl,-Map=output.map -Wl,--gc-sections -lm -o "EM34.elf" @"objects.list"
    arm-none-eabi-gcc.exe: error: _sprintf_float: No such file or directory
    arm-none-eabi-gcc.exe: error: _printf_float: No such file or directory
    make: *** EM34.elf Error 1

    (see attached image)

    LinkerSettings.png (42.06 Kb)

    Posted by tarek bouchkati on 2016-06-20 12:39 Tunisia

    Kevin is right :
    "-u _printf_float" should be after "-specs=nano.specs"

    Notes :
    arm-none-eabi-gcc -mcpu=cortex-m3 -mthumb -mfloat-abi=soft -specs=nosys.specs -specs=nano.specs -Xlinker -u _sprintf_float -Xlinker -u _printf_float -T"../STM32F103CBTx_FLASH.ld" ....

    1. There is no "_sprintf_float"
    2. You do not need Xlinker options
    3. You should have only one -u _printf_float
    4. In (project properties > C/C++ Build > Setings > Tool Settings (TAB) > MCU GCC Linker > Miscellaneous > Linker flags),you should have " -specs=nosys.specs -specs=nano.specs -u _printf_float"
         Posted by sync1 on 2016-06-20 13:22

    Many thanks tarek,

    My problem issue was that was adding the "-u_printf_float" option using the "ADD ICON" which put the required string into the TEXT BOX below ? ..
    This was working ok on previous versions of Sytem32 Workbench ...but ... The Latest version doesn't work like that anymore ... so what I did was to edit/replace the main string at the top ( -specs=nosys.specs -specs=nano.specs ) to what you have shown above .(-specs=nosys.specs -specs=nano.specs -u _printf_float). this worked OK ..
    Thanks again for your help.😀