Hi Carlos,
The sampling rate of the input signal is 48KHz . This means that there is a 20.83uS between every incoming sample . Within this interval , the FIR operation should be completed on that sample. Hence you must make sure that the FIR function is completed within that time interval .
As mentioned in one of the responses above , can you measure time duration from the moment the FIR function is called till the end of that function . If this exceeds the time interval between the two interrupts , the FIR function should be optimized .
You have to exploit the SHARC architecture like using the SIMD mode , circular buffering , MAC instructions etc to get an optimized code .
Regards,
Mahesh