看了一个例程，可以实现了

  #define DEBUG_PRINT(fmt,...)  snprintf(UART_DEBUG_BUFFER, UART_DEBUG_BUFFER_LINE_SIZE, fmt, __VA_ARGS__); \
           UART_DEBUG_PRINT();

#ifdef __DEBUG_UART__
/*******************************************************************
*   Function:    UART_DEBUG_PRINT
*   Description: Prints debug info over the UART using a predefined
*     buffer.
*******************************************************************/
int UART_DEBUG_PRINT(void)
{
unsigned int i = 0;  /* index */
char temp;    /* temp char */

/* loop through the debug buffer until the end, a NULL, or an error */
for ( i = 0; i < UART_DEBUG_BUFFER_LINE_SIZE; i++)
{
  temp = UART_DEBUG_BUFFER[i];

  /* if not NULL then print it */
  if (temp)
  {
   if( 0 == PutChar(temp) )
   {
    /* if error was detected then quit */
    return 0;
   }

   /* if it was a newline we need to add a carriage return */
   if ( 0x0a == temp )
   {
    if( 0 == PutChar(0x0d) )
    {
     /* if error was detected then quit */
     return 0;
    }
   }
  }
  else
  {
   /* else NULL was found */
   return 1;
  }
}

return 1;
}
#endif