Using FIR Function with Streaming Interface - 2022.2 English

The run() function with streaming interfaces and without config input is defined in the HLS namespace similar to this:

 void run(
 hls::stream<in_data_t> &in_V,
 hls::stream<out_data_t> &out_V);

With config input, it is defined similar to this:

 void run(
 hls::stream<in_data_t> &in_V,
 hls::stream<out_data_t> &out_V,
 hls::stream<config_t> &config_V);

The FIR function is defined in the HLS namespace and can be called as follows:

// Create an instance of the FIR
static hls::FIR<STATIC_PARAM> fir1;
// Execute the FIR instance fir1
fir1.run(INPUT_DATA_STREAM, OUTPUT_DATA_STREAM);

The STATIC_PARAM is the static parameterization struct that defines most static parameters for the FIR. Both the input and output data are supplied to the function as hls::stream<>. These ports on the FIR IP will be implemented as AXI4-Stream ports.

Xilinx recommends always using the FIR function in a dataflow region using set_directive_dataflow or #pragma HLS dataflow.

The following code example demonstrates how the FIR IP function can be used.

template<typename data_t, int LENGTH>
void process_fe(data_t in[LENGTH], hls::stream<data_t> &out)
{
    for(unsigned i = 0; i < LENGTH; ++i)
        out.write(in[i]);
}

template<typename data_t, int LENGTH>
void process_be(hls::stream<data_t> &in, data_t out[LENGTH])
{
    for(unsigned i = 0; i < LENGTH; ++i)
        out[i] = in.read();
}

// TOP function
void fir_top(
    data_t in[FIR1_LENGTH],
    data_out_t out[FIR2_LENGTH])
{

    #pragma HLS dataflow

    hls::stream<data_t> fir1_in;
    hls::stream<data_intern_t> fir1_out;
    hls::stream<data_out_t> fir2_out;

    // Create FIR instance
    static hls::FIR<config1> fir1;
    static hls::FIR<config2> fir2;

    //==================================================
    // Dataflow process
    process_fe<data_t, FIR1_LENGTH>(in, fir1_in);
    fir1.run(fir1_in, fir1_out);
    fir2.run(fir1_out, fir2_out);
    process_be<data_out_t, FIR2_LENGTH>(fir2_out, out);
    //==================================================
}