Problem with performance counter??

[Altera_Forum]

hi, 

i use a performance counter and try print execution time of my design but it print the message bellow:( time (sec) is 00??  Total Time: 0 seconds (0 clock-cycles) +---------------+-----+-----------+---------------+-----------+ | Section | % | Time (sec)| Time (clocks)|Occurrences| +---------------+-----+-----------+---------------+-----------+ |z1 | NaN| 0.00000| 0| 0| +---------------+-----+-----------+---------------+-----------+  thank for all members