The number of input/output ports created by a FIR will be given by the formula:
- Number of input ports:
NUM_INPUT_PORTS = TP_PARA_DECI_POLY x TP_SSR x (TP_DUAL_IP + 1) - Number of output ports:
NUM_OUTPUT_PORTS = TP_PARA_INTERP_POLY x TP_SSR x TP_NUM_OUTPUTS
Therefore, the maximum throughput achievable for a given data type, e.g. cint16, can be estimated with:
- maximum theoretical sample rate at input:
THROUGHPUT_IN = NUM_INPUT_PORTS x 1 GSa/s, - maximum theoretical sample rate at output =
THROUGHPUT_OUT = NUM_OUTPUT_PORTS x 1 GSa/s.
Rate-changing FIR Throughput
For rate changers, the bandwidth of either the input or output port, depending on whether it is a decimator or an interpolator, may limit the throughput of the filter.
For example, an interpolator with interpolation factor of 3 produces three times the number of outputs as inputs. However, the AIE stream port bandwidth is the same for input and output.
Hence, if the output runs at maximum bandwidth, the input would need to run at 1/3rd its maximum bandwidth, and we are forced to underutilize the input stream of the filter at only 33 percent efficiency.
However, if we are able to split the operation of the interpolator over 3 kernels, broadcast the input stream to their inputs, and operate the kernels at maximum performance, it will be possible to use both the input and output bandwidths at their maximum bandwidths.