[STM32] 解決 sprintf...etc 或 maco函數無法編譯的問題

接上一篇,

如果遭遇到, 當使用了一些 standard C 函式庫之後, 且 compile 無法正常編譯過,

Error Message:

c:/program files (x86)/gnu tools arm embedded/5.2 2015q4/bin/../lib/gcc/arm-none-eabi/5.2.1/../../../../arm-none-eabi/lib/armv7-m\libg.a(lib_a-sbrkr.o): In function `_sbrk_r':

sbrkr.c:(.text._sbrk_r+0xc): undefined reference to `_sbrk'

collect2.exe: error: ld returned 1 exit status

make: *** [USART_String.elf] Error 1

請試著使用以下方法,

1, 在 stm32_flash.ld 檔案找到如下這段, 然後在最後面加上 PROVIDE (__HEAP_START = _end);  

  /* Uninitialized data section */

  . = ALIGN(4);

  .bss :

  {

    /* This is used by the startup in order to initialize the .bss secion */

    _sbss = .;         /* define a global symbol at bss start */

    __bss_start__ = _sbss;

    *(.bss)

    *(.bss*)

    *(COMMON)

    . = ALIGN(4);

    _ebss = .;         /* define a global symbol at bss end */

    __bss_end__ = _ebss;

  } >RAM

  PROVIDE ( end = _ebss );

  PROVIDE ( _end = _ebss );

  PROVIDE (__HEAP_START = _end);

2, 在 USER 資料夾內, 創建一個新的檔案 syscalls.c , 並在裡面添加下面這些 code.

#include <sys/types.h>

// for use malloc sprintf function

extern int  __HEAP_START;

caddr_t _sbrk ( int incr ){

  static unsigned char *heap = NULL;

  unsigned char *prev_heap;

  if (heap == NULL) {

    heap = (unsigned char *)&__HEAP_START;

  }

  prev_heap = heap;

  heap += incr;

  return (caddr_t) prev_heap;

}

儲存, 應該就可以正常編譯了.