A problem when using DSP_fft16x16t in C6416

Hello experts,
    I encounter a problem when I am using the TMS320C6416. In my dsp program, there are 2 external interputions which are all trigged by
rising edge. I use FPGA to generate the interputions which appear periodically.
    In my program, I want to accomplish the fft function. I use the DSP_fft16x16t to do the FFT.
    Here are my problem. When I use the DSP_fft16x16t and run the program, I find the program can't go into the interputions. I check the
external interputions pulse, they still appear periodically. But the program can't go into the interputions.
    When I delete the function DSP_fft16x16t or I change the DSP_fft16x16t to DSP_fft32x32, the program works properly and can go
into the interputions.
    Based the above description, I think maybe the problem is that I am not using the DSP_fft16x16t properly, so it affects the interpution
working. I also check the DSP_fft16x16t.h file and find no clue.
    Can someone give me some advice? Thank you very much.