概述

最近公司项目换另一款gsensor，用到了浮点数打印。又不想使用串口来打印数据，在此做个笔录，通过修改源码方式实现。

一、修改源码

1、在 SEGGER_RTT_printf.c 中的 int SEGGER_RTT_vprintf(unsigned BufferIndex, const char * sFormat, va_list * pParamList)函数，增加以下
?case 'f':
?case 'F': 语句

/*********************************************************************
*
*       SEGGER_RTT_vprintf
*
*  Function description
*    Stores a formatted string in SEGGER RTT control block.
*    This data is read by the host.
*
*  Parameters
*    BufferIndex  Index of "Up"-buffer to be used. (e.g. 0 for "Terminal")
*    sFormat      Pointer to format string
*    pParamList   Pointer to the list of arguments for the format string
*
*  Return values
*    >= 0:  Number of bytes which have been stored in the "Up"-buffer.
*     < 0:  Error
*/
int SEGGER_RTT_vprintf(unsigned BufferIndex, const char * sFormat, va_list * pParamList) {
  char c;
  SEGGER_RTT_PRINTF_DESC BufferDesc;
  int v;
  unsigned NumDigits;
  unsigned FormatFlags;
  unsigned FieldWidth;
  char acBuffer[SEGGER_RTT_PRINTF_BUFFER_SIZE];

  BufferDesc.pBuffer        = acBuffer;
  BufferDesc.BufferSize     = SEGGER_RTT_PRINTF_BUFFER_SIZE;
  BufferDesc.Cnt            = 0u;
  BufferDesc.RTTBufferIndex = BufferIndex;
  BufferDesc.ReturnValue    = 0;

  do {
    c = *sFormat;
    sFormat++;
    if (c == 0u) {
      break;
    }
    if (c == '%') {
      //
      // Filter out flags
      //
      FormatFlags = 0u;
      v = 1;
      do {
        c = *sFormat;
        switch (c) {
        case '-': FormatFlags |= FORMAT_FLAG_LEFT_JUSTIFY; sFormat++; break;
        case '0': FormatFlags |= FORMAT_FLAG_PAD_ZERO;     sFormat++; break;
        case '+': FormatFlags |= FORMAT_FLAG_PRINT_SIGN;   sFormat++; break;
        case '#': FormatFlags |= FORMAT_FLAG_ALTERNATE;    sFormat++; break;
        default:  v = 0; break;
        }
      } while (v);
      //
      // filter out field with
      //
      FieldWidth = 0u;
      do {
        c = *sFormat;
        if ((c < '0') || (c > '9')) {
          break;
        }
        sFormat++;
        FieldWidth = (FieldWidth * 10u) + ((unsigned)c - '0');
      } while (1);

      //
      // Filter out precision (number of digits to display)
      //
      NumDigits = 0u;
      c = *sFormat;
      if (c == '.') {
        sFormat++;
        do {
          c = *sFormat;
          if ((c < '0') || (c > '9')) {
            break;
          }
          sFormat++;
          NumDigits = NumDigits * 10u + ((unsigned)c - '0');
        } while (1);
      }
      //
      // Filter out length modifier
      //
      c = *sFormat;
      do {
        if ((c == 'l') || (c == 'h')) {
          sFormat++;
          c = *sFormat;
        } else {
          break;
        }
      } while (1);
      //
      // Handle specifiers
      //
      switch (c) {
      case 'c': {
        char c0;
        v = va_arg(*pParamList, int);
        c0 = (char)v;
        _StoreChar(&BufferDesc, c0);
        break;
      }
      case 'd':
        v = va_arg(*pParamList, int);
        _PrintInt(&BufferDesc, v, 10u, NumDigits, FieldWidth, FormatFlags);
        break;
      case 'u':
        v = va_arg(*pParamList, int);
        _PrintUnsigned(&BufferDesc, (unsigned)v, 10u, NumDigits, FieldWidth, FormatFlags);
        break;
      case 'x':
      case 'X':
        v = va_arg(*pParamList, int);
        _PrintUnsigned(&BufferDesc, (unsigned)v, 16u, NumDigits, FieldWidth, FormatFlags);
        break;
      case 's':
        {
          const char * s = va_arg(*pParamList, const char *);
          do {
            c = *s;
            s++;
            if (c == '\0') {
              break;
            }
           _StoreChar(&BufferDesc, c);
          } while (BufferDesc.ReturnValue >= 0);
        }
        break;
      case 'p':
        v = va_arg(*pParamList, int);
        _PrintUnsigned(&BufferDesc, (unsigned)v, 16u, 8u, 8u, 0u);
        break;
      case '%':
        _StoreChar(&BufferDesc, '%');
        break;
	  // Add the ability to output floating point numbers. It has two decimal places by default.
	  #if 0
	  case 'f':
	  case 'F':
	  {
	  	char ch[10]={0};
	  	const char * s=ch;
	  	double a = va_arg(*pParamList, double);
	  	sprintf(ch,"%4.3f",a);
	  	do{
			c = *s;
			s++;
			if (c == '\0') break;
			_StoreChar(&BufferDesc, c);
		}while(BufferDesc.ReturnValue >= 0);
	  }break;
	  #else
	  case 'f':
	  case 'F': {
		float fv = (float)va_arg(*pParamList, double);    // Retrieves the input floating point value
		if(fv < 0) _StoreChar(&BufferDesc, '-');          // Judge the sign
		v = abs((int)fv);                                 // Take the positive integer part
		_PrintInt(&BufferDesc, v, 10u, NumDigits, FieldWidth, FormatFlags);  // According to an integer
		_StoreChar(&BufferDesc, '.');                                        // Display decimal point
		v = abs((int)(fv * 1000));               
		v = v % 1000;
		_PrintInt(&BufferDesc, v, 10u, 3, FieldWidth, FormatFlags);          // Display three decimal places
	  }break;
	  #endif
      default:
        break;
      }
      sFormat++;
    } else {
      _StoreChar(&BufferDesc, c);
    }
  } while (BufferDesc.ReturnValue >= 0);

  if (BufferDesc.ReturnValue > 0) {
    //
    // Write remaining data, if any
    //
    if (BufferDesc.Cnt != 0u) {
      SEGGER_RTT_Write(BufferIndex, acBuffer, BufferDesc.Cnt);
    }
    BufferDesc.ReturnValue += (int)BufferDesc.Cnt;
  }
  return BufferDesc.ReturnValue;
}