Task stack size of RTX kernel

Hi,

I am trying to use the RTC of LPC2378 and the RTX kernel of KEIL.

The below is the code of one of my tasks.

void job3 (void) __task
{
        while(1)
        {
                snprintf(FMTstring, 29, "%04d-%02d-%02d Y%03d-W%01d %02d:%02d:%02d\r",
                        RTC_YEAR, RTC_MONTH, RTC_DOM,
                        RTC_DOY,  RTC_DOW,
                        RTC_HOUR, RTC_MIN, RTC_SEC );

                UART0sbWRITE( (BYTE *)FMTstring, 29 );
                UART0sendKICK();
                os_dly_wait (100);
        }
}

I found that, I need to set the "Task stack size" to 348 bytes, otherwise I will get a stack overflow. Since I do not declare any variable in this task, why it needs so large stack?