vsPrintf() takes too much memory in RTOS.

gridsense wrote on Sunday, October 23, 2011:

In my code, there is a function “xUartPrintF()” which get called by every task to print out message,  it calls a library function “vsprintf()”. I find that “vsprintf()” take too much memory, is there anyway to avoid it?

Here is the code: 

static char PrintFBuffer;

UART_STATUS xUartPrintF(const char* format, …)
  va_list args;

  /* Open variable parameter list */

  /* Format the string */
  if (!vsprintf(PrintFBuffer,format,args))
    return UART_STATUS_FAIL;

  /* Send the string via RS232 */
  if (xUartTransmit(PrintFBuffer) != UART_STATUS_SUCCESS)
    return UART_STATUS_FAIL;

  /* End parameter list */


rtel wrote on Sunday, October 23, 2011:

vsPrintf() takes too much memory in RTOS

How much memory it takes is a characteristic of the library you are using, not of the RTOS.  Some standard libraries are massive, consume monster amounts of stack, and even dynamically allocate memory within their implementations - while others are lean and mean and work well in resource constrained embedded systems.

get called by every task to print out message

As this function is a global resource and not re-entrant, I hope it has some external mutual exclusion being used.

is there anyway to avoid it

There is a minimal sprintf() implementation provided with the FreeRTOS distribution (as a third party piece of code).  It can be used if you don’t want to print out floating point numbers.  Find (multiple copies of) it by searching the FreeRTOS/Demo directory for a file called printf-stdarg.c.  Including it in your project should allow its implementation to be used in preference to the standard libraries version.  Don’t use the snprintf() version defined in the same file though, as it is not really implemented, just included to allow linking.

Hope that helps.