For filters with an integer rate change, the core accepts input samples at fixed intervals and produces an output that has a fixed sample period. A decimation by 3 filter with an input sampling frequency of 50 MHz and a clock frequency of 200 MHz has an input sample period of four clocks cycles and an output sample period of 12 clock cycles.
The exception to this is interpolating filters with a rate change that when divided into the input sample period leaves a non-zero remainder; for example, an interpolation by 3 filter with an input sampling frequency of 25 MHz and a clock frequency of 200 MHz. The input sample period is 8 but the output sample period needs to be 2.666…7. In this circumstance the core generates the interpolated output samples with a period of 2 but following the final interpolated output sample, there is an additional 2 clock cycles where no outputs are produced. This generates three output samples for every eight clock cycles and an effective sample rate of 2.666…7 clock cycles.