Xiang Liu,
Can you run the DSP_fft16x16t program by calling it from a task or from main? Will it run correctly in that case?
If you set a breakpoint in the interrupt service routine before the call to the DSP_fft16x16t function, will it reach that breakpoint the first time?
Do you find anything different in the description of the DSP_fft16x16t from the 32x32 version that might explain a difference?
Are the arguments different for the two fft functions, in a way that could help explain this odd behavior?
How are you determining whether the Interrupt Service Routine (ISR) is executed or not?
Regards,
RandyP