In some modes of operation, the FIR requires an additional input to configure how the coefficients are used. For a complete description of which modes require this input configuration, refer to the FIR Compiler LogiCORE IP Product Guide (PG149).
This input configuration can be performed in the C code using a standard ap_int.h 8-bit data type. In this example, the header file fir_top.h
specifies the use of the FIR and ap_fixed
libraries, defines a number of the design parameter values and then defines some fixed-point types based on these:
#include "ap_fixed.h"
#include "hls_fir.h"
const unsigned FIR_LENGTH = 21;
const unsigned INPUT_WIDTH = 16;
const unsigned INPUT_FRACTIONAL_BITS = 0;
const unsigned OUTPUT_WIDTH = 24;
const unsigned OUTPUT_FRACTIONAL_BITS = 0;
const unsigned COEFF_WIDTH = 16;
const unsigned COEFF_FRACTIONAL_BITS = 0;
const unsigned COEFF_NUM = 7;
const unsigned COEFF_SETS = 3;
const unsigned INPUT_LENGTH = FIR_LENGTH;
const unsigned OUTPUT_LENGTH = FIR_LENGTH;
const unsigned CHAN_NUM = 1;
typedef ap_fixed<INPUT_WIDTH, INPUT_WIDTH - INPUT_FRACTIONAL_BITS> s_data_t;
typedef ap_fixed<OUTPUT_WIDTH, OUTPUT_WIDTH - OUTPUT_FRACTIONAL_BITS> m_data_t;
typedef ap_uint<8> config_t;
In the top-level code, the information in the header file is included, the static parameterization struct is created using the same constant values used to specify the bit-widths, ensuring the C code and FIR configuration match, and the coefficients are specified. At the top-level, an input configuration, defined in the header file as 8-bit data, is passed into the FIR.
#include "fir_top.h"
struct param1 : hls::ip_fir::params_t {
static const double coeff_vec[total_num_coeff];
static const unsigned input_length = INPUT_LENGTH;
static const unsigned output_length = OUTPUT_LENGTH;
static const unsigned num_coeffs = COEFF_NUM;
static const unsigned coeff_sets = COEFF_SETS;
};
const double param1::coeff_vec[total_num_coeff] =
{6,0,-4,-3,5,6,-6,-13,7,44,64,44,7,-13,-6,6,5,-3,-4,0,6};
void dummy_fe(s_data_t in[INPUT_LENGTH], s_data_t out[INPUT_LENGTH],
config_t* config_in, config_t* config_out)
{
*config_out = *config_in;
for(unsigned i = 0; i < INPUT_LENGTH; ++i)
out[i] = in[i];
}
void dummy_be(m_data_t in[OUTPUT_LENGTH], m_data_t out[OUTPUT_LENGTH])
{
for(unsigned i = 0; i < OUTPUT_LENGTH; ++i)
out[i] = in[i];
}
// DUT
void fir_top(s_data_t in[INPUT_LENGTH],
m_data_t out[OUTPUT_LENGTH],
config_t* config)
{
s_data_t fir_in[INPUT_LENGTH];
m_data_t fir_out[OUTPUT_LENGTH];
config_t fir_config;
// Create struct for config
static hls::FIR<param1> fir1;
//==================================================
// Dataflow process
dummy_fe(in, fir_in, config, &fir_config);
fir1.run(fir_in, fir_out, &fir_config);
dummy_be(fir_out, out);
//==================================================
}
Design examples using the FIR C library are provided in the Vitis HLS examples and can be accessed using menu option .