File content as of revision 1:f69ec4c889ff:

#include "hydro_dsp.h"

arm_iir_lattice_instance_q15 iir_filter[NUM_CHANNELS];

// TODO: need an A and B for each possible frequency
// our pinger: 27k
// dave's pinger(s): TODO: ask about this
q15_t A_27k0[FILTER_ORDER] = {};
q15_t B_27k0[FILTER_ORDER+1] = {};

// Set these variables to select which set of coefficients (taps) we use
q15_t* A_select = A_27k0;
q15_t* B_select = B_27k0;

q15_t state_arr[NUM_CHANNELS][FILTER_ORDER + BLOCK_SIZE];

q15_t filtered[BLOCK_SIZE];

void setup_dsp()
{
    memset(state_arr, 0, 2*NUM_CHANNELS*(FILTER_ORDER + BLOCK_SIZE));
    for (int i = 0; i < NUM_CHANNELS; i++) {
        arm_iir_lattice_init_q15(iir_filter+i, FILTER_ORDER, A_27k0, B_27k0, state_arr[i], BLOCK_SIZE);
    }
}

// Figure out where the wave starts in the filtered output
// TODO: does this work?
// Returns the index of the first "high" in the signal or -1 if there is none
int find_timestamp_tdoa(q15_t* filtered)
{
    // Uncomment the num_hits stuff if our filtering sucks
    //char num_hits = 0;
    for (int j = 0; j < BLOCK_SIZE; j++)
    {
        if (filtered[j] > TDOA_THRESH || filtered[j] < -1 * TDOA_THRESH)
        {
            return j;
            /*num_hits++;
            if (num_hits > TDOA_MIN_NUM_HITS)
            {
                return j;            
            }*/
        }
    }
    
    return -1;
}