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kai23
kai23
Associate
November 25, 2016
Question

Scanf with Nucleo-F401RE & STM Eclipse C IDE

  • November 25, 2016
  • 5 replies
  • 1254 views
Posted on November 25, 2016 at 12:23

Hello,

first i have to say, i´m a bloody Beginner with C and STM.

Never the less, i have the following problem.

I just want do make it possible to communicate with Terminal (Putty, Terra Term,...).

Printf seems to work, there is a good example in Cubemx.

But scanf is not working. Whatever i try, my program is not able to process the input. As well at the Terminal there is no input seen unless i activate ''local echo'' at the terminal.

I have tried different example code, sometimes the programm stucks in my while loop and is waiting for an input. And without while loop, the input is skipped.

I´m nearly sure this depends on Getchar_Prototype but for me, it is still not clear what i have to do.

Maybe someone could help or knows some good online Tutorials/Books.

Thanks Kai
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    5 replies

    Tesla DeLorean
    Tesla DeLorean
    Guru
    November 25, 2016
    Posted on November 26, 2016 at 00:40

    You'll probably find most embedded solutions don't use scanf() as the primary means of input. Think about managing the input/output more directly, and use sscanf() on the string to get from that.

    Tips, Buy me a coffee, or three.. PayPal Venmo (See Profile) Up vote any posts that you find helpful, it shows what's working..
    Andrei Chichak
    Andrei Chichak
    Lead
    November 26, 2016
    Posted on November 26, 2016 at 06:21

    Wait, I think I might know this one; I have seen that some of the compiler/libraries (newlib) use buffering on input.

    Try holding down a key on your keyboard for about 210 seconds. I seem to remember that the buffer was about 2K and you get about 10 characters per second off of a keyboard.

    Just a shot in the dark.
    Andrei Chichak
    Andrei Chichak
    Lead
    November 26, 2016
    Posted on November 26, 2016 at 06:34

    Kay, found it. The compiler was gcc from sw4stm32 (ac6). The buffer was 1024 characters, and the command to turn off buffering is:

    .ExternalClassCE8F3B77326446E0B6CCD68E5AF37C27 p.p1 {margin:0.0px 0.0px 0.0px 0.0px;font:12.0px 'Courier New';} .ExternalClassCE8F3B77326446E0B6CCD68E5AF37C27 span.s1 {;} .ExternalClassCE8F3B77326446E0B6CCD68E5AF37C27 span.s2 {color:#793d93;} .ExternalClassCE8F3B77326446E0B6CCD68E5AF37C27 span.Apple-tab-span {white-space:pre;}

    setvbuf

    (stdin, NULL, _IONBF, 0);

    Put this in your program somewhere before your big loop.
    kai23
    kai23Author
    Associate
    November 28, 2016
    Posted on November 28, 2016 at 10:07

    Many thanks, this is what i was searching for :)

    It works now.

    That was not easy for a beginner like me.

    Kaily

    Andrei Chichak
    Andrei Chichak
    Lead
    November 28, 2016
    Posted on November 28, 2016 at 20:49

    No, that definitely isn't your fault. I taught an intro to embedded systems class at the local maker space and this came up when I was teaching the UART section.

    I'm doing a brain dump of my course notes on the Embedded.FM blog (embedded.fm/blog) and this week's topic is - UARTs.

    I will be giving you this tidbit in about two weeks. There's quite a bit to go over yet.

    I'm glad I could help.

    Andrei from The Great White North

    (as seen on the embedded.fm podcast and blog)
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