filter_ex3_biquad_cascade_df1_q15.c

This example demonstrates how to use the msp_biquad_cascade_df1_q15 API to filter 16-bit input data using the Direct Form I (df1) biquad function and a cascade of filter stages.

//******************************************************************************
// IIR filter using a cascaded DF1 biquad.
//
// Brent Peterson, Jeremy Friesenhahn
// Texas Instruments Inc.
// April 2016
//******************************************************************************
#include "msp430.h"

#include <math.h>
#include <stdint.h>
#include <string.h>
#include <stdbool.h>

#include "DSPLib.h"

/* Include header generated from DSPLib GUI here (optional). */
//#include "myCoeffs_ex3.h"

/* Input signal parameters */
#define FS                  8192
#define SIGNAL_LENGTH       256
#define SIGNAL_FREQUENCY1   200
#define SIGNAL_AMPLITUDE1   0.6
#define SIGNAL_FREQUENCY2   2100
#define SIGNAL_AMPLITUDE2   0.15

/* Constants */
#define PI                  3.1415926536

/* Define example coefficients if no DSPLib GUI header is provided. */
#ifndef FILTER_COEFFS_EX3
/* Second-order sections for 16th order low pass filter (Fs=8192, Fc=1800) */
const msp_biquad_df1_q15_coeffs FILTER_COEFFS_EX3[8] = {
    {
        .b0     = _Q15(+0.312963),
        .b1By2  = _Q15(+0.608536/2),
        .b2     = _Q15(+0.312963),
        .a1By2  = _Q15(-0.215187/2),
        .a2     = _Q15(-0.019276)
    },
    {
        .b0     = _Q15(+0.341644),
        .b1By2  = _Q15(+0.533004/2),
        .b2     = _Q15(+0.341644),
        .a1By2  = _Q15(-0.145445/2),
        .a2     = _Q15(-0.070846)
    },
    {
        .b0     = _Q15(+0.393284),
        .b1By2  = _Q15(+0.399958/2),
        .b2     = _Q15(+0.393284),
        .a1By2  = _Q15(-0.021883/2),
        .a2     = _Q15(-0.164643)
    },
    {
        .b0     = _Q15(+0.459362),
        .b1By2  = _Q15(+0.236817/2),
        .b2     = _Q15(+0.459362),
        .a1By2  = _Q15(+0.131385/2),
        .a2     = _Q15(-0.286925)
    },
    {
        .b0     = _Q15(+0.532049),
        .b1By2  = _Q15(+0.070226/2),
        .b2     = _Q15(+0.532049),
        .a1By2  = _Q15(+0.291215/2),
        .a2     = _Q15(-0.425539)
    },
    {
        .b0     = _Q15(+0.606300),
        .b1By2  = _Q15(-0.079576/2),
        .b2     = _Q15(+0.606300),
        .a1By2  = _Q15(+0.440602/2),
        .a2     = _Q15(-0.573626)
    },
    {
        .b0     = _Q15(+0.680340),
        .b1By2  = _Q15(-0.199067/2),
        .b2     = _Q15(+0.680340),
        .a1By2  = _Q15(+0.569203/2),
        .a2     = _Q15(-0.730815)
    },
    {
        .b0     = _Q15(+0.755460),
        .b1By2  = _Q15(-0.278629/2),
        .b2     = _Q15(+0.755460),
        .a1By2  = _Q15(+0.671286/2),
        .a2     = _Q15(-0.903577)
    }
};
#endif

/* Filter parameters */
#define FILTER_LENGTH   (SIGNAL_LENGTH)
#define FILTER_STAGES   (sizeof(FILTER_COEFFS_EX3)/sizeof(msp_biquad_df1_q15_coeffs))

/* Filter coefficients */
DSPLIB_DATA(filterCoeffs,4)
msp_biquad_df1_q15_coeffs filterCoeffs[FILTER_STAGES];

/* Filter input signal */
DSPLIB_DATA(input,4)
_q15 input[SIGNAL_LENGTH];

/* Temporary data array for processing */
DSPLIB_DATA(temp,4)
_q15 temp[SIGNAL_LENGTH];

/* Filter result */
DSPLIB_DATA(result,4)
_q15 result[SIGNAL_LENGTH];

/* State buffer */
DSPLIB_DATA(states,4)
msp_biquad_df1_q15_states states[FILTER_STAGES];

/* Benchmark cycle counts */
volatile uint32_t cycleCount = 0;

/* Function prototypes */
extern void initSignal(void);

void main(void)
{
    msp_status status;
    msp_fill_q15_params fillParams;
    msp_biquad_cascade_df1_q15_params df1Params;
    
    /* Disable WDT. */
    WDTCTL = WDTPW + WDTHOLD;

#ifdef __MSP430_HAS_PMM__
    /* Disable GPIO power-on default high-impedance mode for FRAM devices */
    PM5CTL0 &= ~LOCKLPM5;
#endif

    /* Initialize input signal */
    initSignal();
    
    /* Initialize filter coefficients. */
    memcpy(filterCoeffs, FILTER_COEFFS_EX3, sizeof(filterCoeffs));

    /* Zero initialize filter states. */
    fillParams.length = sizeof(states)/sizeof(_q15);
    fillParams.value = 0;
    status = msp_fill_q15(&fillParams, (void *)states);
    msp_checkStatus(status);
    
    /* Initialize the parameter structure. */
    df1Params.length = FILTER_LENGTH;
    df1Params.stages = FILTER_STAGES;
    df1Params.coeffs = filterCoeffs;
    df1Params.states = states;
    
    /* Invoke the msp_biquad_cascade_df1_q15 function. */
    msp_benchmarkStart(MSP_BENCHMARK_BASE, 8);
    status = msp_biquad_cascade_df1_q15(&df1Params, input, result);
    cycleCount = msp_benchmarkStop(MSP_BENCHMARK_BASE);
    msp_checkStatus(status);
    
    /* End of program. */
    __no_operation();
}

void initSignal(void)
{
    msp_status status;
    msp_add_q15_params addParams;
    msp_sinusoid_q15_params sinParams;

    /* Generate Q15 input signal 1 */
    sinParams.length = SIGNAL_LENGTH;
    sinParams.amplitude = _Q15(SIGNAL_AMPLITUDE1);
    sinParams.cosOmega = _Q15(cosf(2*PI*SIGNAL_FREQUENCY1/FS));
    sinParams.sinOmega = _Q15(sinf(2*PI*SIGNAL_FREQUENCY1/FS));
    status = msp_sinusoid_q15(&sinParams, input);
    msp_checkStatus(status);

    /* Generate Q15 input signal 2 to temporary array */
    sinParams.length = SIGNAL_LENGTH;
    sinParams.amplitude = _Q15(SIGNAL_AMPLITUDE2);
    sinParams.cosOmega = _Q15(cosf(2*PI*SIGNAL_FREQUENCY2/FS));
    sinParams.sinOmega = _Q15(sinf(2*PI*SIGNAL_FREQUENCY2/FS));
    status = msp_sinusoid_q15(&sinParams, temp);
    msp_checkStatus(status);

    /* Add input signals */
    addParams.length = SIGNAL_LENGTH;
    status = msp_add_q15(&addParams, input, temp, input);
    msp_checkStatus(status);
}