alt_timestamp returns the same value

Hello, I'm trying below:
int main()
{
alt_u32 t1;
alt_u32 t2;
alt_u32 t3;

int ret = alt_timestamp_start();
t1 = alt_timestamp();
usleep(1000000);
t2 = alt_timestamp();
t3 = alt_timestamp_freq();

return 0;
}

ret is 0, t3 is 50000000(the input clock of Interval Timer object),
but t1 and t2 always show 4209704959.
It seems that the Timer is not ticking.
I also tried alt_nticks which always returned 0;
I wonder what might be the problem here.

-Cyclone V Dev Board
-QuartusII 15.0(64bit), Qsys on Win7
-NiosI 15.0 Software Build Tools for Eclipse

Thanks in advance.