/** \file algorithm.cpp ******************************************************

*

* Project: MAXREFDES117#

* Filename: algorithm.cpp

* Description: This module calculates the heart rate/SpO2 level

*

*

* --------------------------------------------------------------------

*

* This code follows the following naming conventions:

*

* char ch_pmod_value

* char (array) s_pmod_s_string[16]

* float f_pmod_value

* int32_t n_pmod_value

* int32_t (array) an_pmod_value[16]

* int16_t w_pmod_value

* int16_t (array) aw_pmod_value[16]

* uint16_t uw_pmod_value

* uint16_t (array) auw_pmod_value[16]

* uint8_t uch_pmod_value

* uint8_t (array) auch_pmod_buffer[16]

* uint32_t un_pmod_value

* int32_t * pn_pmod_value

*

* ------------------------------------------------------------------------- */

/*******************************************************************************

* Copyright (C) 2016 Maxim Integrated Products, Inc., All Rights Reserved.

*

* Permission is hereby granted, free of charge, to any person obtaining a

* copy of this software and associated documentation files (the "Software"),

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*

* The above copyright notice and this permission notice shall be included

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*

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* IN NO EVENT SHALL MAXIM INTEGRATED BE LIABLE FOR ANY CLAIM, DAMAGES

* OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,

* ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR

* OTHER DEALINGS IN THE SOFTWARE.

*

* Except as contained in this notice, the name of Maxim Integrated

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*

* The mere transfer of this software does not imply any licenses

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*******************************************************************************

*/

#include <stdint.h>

#include "algorithm.h"

//#include "arduino.h"

void maxim_heart_rate_and_oxygen_saturation(uint32_t *pun_ir_buffer, int32_t n_ir_buffer_length, uint32_t *pun_red_buffer, int32_t *pn_spo2, int8_t *pch_spo2_valid,

int32_t *pn_heart_rate, int8_t *pch_hr_valid)

/**

* \brief Calculate the heart rate and SpO2 level

* \par Details

* By detecting peaks of PPG cycle and corresponding AC/DC of red/infra-red signal, the an_ratio for the SPO2 is computed.

* Since this algorithm is aiming for Arm M0/M3. formaula for SPO2 did not achieve the accuracy due to register overflow.

* Thus, accurate SPO2 is precalculated and save longo uch_spo2_table[] per each an_ratio.

*

* \param[in] *pun_ir_buffer - IR sensor data buffer

* \param[in] n_ir_buffer_length - IR sensor data buffer length

* \param[in] *pun_red_buffer - Red sensor data buffer

* \param[out] *pn_spo2 - Calculated SpO2 value

* \param[out] *pch_spo2_valid - 1 if the calculated SpO2 value is valid

* \param[out] *pn_heart_rate - Calculated heart rate value

* \param[out] *pch_hr_valid - 1 if the calculated heart rate value is valid

*

* \retval None

*/

{

uint32_t un_ir_mean,un_only_once ;

int32_t k, n_i_ratio_count;

int32_t i, s, m, n_exact_ir_valley_locs_count, n_middle_idx;

int32_t n_th1, n_npks, n_c_min;

int32_t an_ir_valley_locs[15] ;

int32_t n_peak_interval_sum;

int32_t n_y_ac, n_x_ac;

int32_t n_spo2_calc;

int32_t n_y_dc_max, n_x_dc_max;

int32_t n_y_dc_max_idx, n_x_dc_max_idx;

int32_t an_ratio[5], n_ratio_average;

int32_t n_nume, n_denom ;

// calculates DC mean and subtract DC from ir

un_ir_mean =0;

for (k=0 ; k<n_ir_buffer_length ; k++ ) un_ir_mean += pun_ir_buffer[k] ;

un_ir_mean =un_ir_mean/n_ir_buffer_length ;

// remove DC and invert signal so that we can use peak detector as valley detector

for (k=0 ; k<n_ir_buffer_length ; k++ )

an_x[k] = -1*(pun_ir_buffer[k] - un_ir_mean) ;

// 4 pt Moving Average

for(k=0; k< BUFFER_SIZE-MA4_SIZE; k++){

an_x[k]=( an_x[k]+an_x[k+1]+ an_x[k+2]+ an_x[k+3])/(int)4;

}

// calculate threshold

n_th1=0;

for ( k=0 ; k<BUFFER_SIZE ;k++){

n_th1 += an_x[k];

}

n_th1= n_th1/ ( BUFFER_SIZE);

if( n_th1<30) n_th1=30; // min allowed

if( n_th1>60) n_th1=60; // max allowed

for ( k=0 ; k<15;k++) an_ir_valley_locs[k]=0;

// since we flipped signal, we use peak detector as valley detector

maxim_find_peaks( an_ir_valley_locs, &n_npks, an_x, BUFFER_SIZE, n_th1, 4, 15 );//peak_height, peak_distance, max_num_peaks

n_peak_interval_sum =0;

if (n_npks>=2){

for (k=1; k<n_npks; k++) n_peak_interval_sum += (an_ir_valley_locs[k] -an_ir_valley_locs[k -1] ) ;

n_peak_interval_sum =n_peak_interval_sum/(n_npks-1);

*pn_heart_rate =(int32_t)( (FS*60)/ n_peak_interval_sum );

*pch_hr_valid = 1;

}

else {

*pn_heart_rate = -999; // unable to calculate because # of peaks are too small

*pch_hr_valid = 0;

}

// load raw value again for SPO2 calculation : RED(=y) and IR(=X)

for (k=0 ; k<n_ir_buffer_length ; k++ ) {

an_x[k] = pun_ir_buffer[k] ;

an_y[k] = pun_red_buffer[k] ;

}

// find precise min near an_ir_valley_locs

n_exact_ir_valley_locs_count =n_npks;

//using exact_ir_valley_locs , find ir-red DC andir-red AC for SPO2 calibration an_ratio

//finding AC/DC maximum of raw

n_ratio_average =0;

n_i_ratio_count = 0;

for(k=0; k< 5; k++) an_ratio[k]=0;

for (k=0; k< n_exact_ir_valley_locs_count; k++){

if (an_ir_valley_locs[k] > BUFFER_SIZE ){

*pn_spo2 = -999 ; // do not use SPO2 since valley loc is out of range

*pch_spo2_valid = 0;

return;

}

}

// find max between two valley locations

// and use an_ratio betwen AC compoent of Ir & Red and DC compoent of Ir & Red for SPO2

for (k=0; k< n_exact_ir_valley_locs_count-1; k++){

n_y_dc_max= -16777216 ;

n_x_dc_max= -16777216;

if (an_ir_valley_locs[k+1]-an_ir_valley_locs[k] >3){

for (i=an_ir_valley_locs[k]; i< an_ir_valley_locs[k+1]; i++){

if (an_x[i]> n_x_dc_max) {n_x_dc_max =an_x[i]; n_x_dc_max_idx=i;}

if (an_y[i]> n_y_dc_max) {n_y_dc_max =an_y[i]; n_y_dc_max_idx=i;}

}

n_y_ac= (an_y[an_ir_valley_locs[k+1]] - an_y[an_ir_valley_locs[k] ] )*(n_y_dc_max_idx -an_ir_valley_locs[k]); //red

n_y_ac= an_y[an_ir_valley_locs[k]] + n_y_ac/ (an_ir_valley_locs[k+1] - an_ir_valley_locs[k]) ;

n_y_ac= an_y[n_y_dc_max_idx] - n_y_ac; // subracting linear DC compoenents from raw

n_x_ac= (an_x[an_ir_valley_locs[k+1]] - an_x[an_ir_valley_locs[k] ] )*(n_x_dc_max_idx -an_ir_valley_locs[k]); // ir

n_x_ac= an_x[an_ir_valley_locs[k]] + n_x_ac/ (an_ir_valley_locs[k+1] - an_ir_valley_locs[k]);

n_x_ac= an_x[n_y_dc_max_idx] - n_x_ac; // subracting linear DC compoenents from raw

n_nume=( n_y_ac *n_x_dc_max)>>7 ; //prepare X100 to preserve floating value

n_denom= ( n_x_ac *n_y_dc_max)>>7;

if (n_denom>0 && n_i_ratio_count <5 && n_nume != 0)

{

an_ratio[n_i_ratio_count]= (n_nume*100)/n_denom ; //formular is ( n_y_ac *n_x_dc_max) / ( n_x_ac *n_y_dc_max) ;

n_i_ratio_count++;

}

}

}

// choose median value since PPG signal may varies from beat to beat

maxim_sort_ascend(an_ratio, n_i_ratio_count);

n_middle_idx= n_i_ratio_count/2;

if (n_middle_idx >1)

n_ratio_average =( an_ratio[n_middle_idx-1] +an_ratio[n_middle_idx])/2; // use median

else

n_ratio_average = an_ratio[n_middle_idx ];

if( n_ratio_average>2 && n_ratio_average <184){

n_spo2_calc= uch_spo2_table[n_ratio_average] ;

*pn_spo2 = n_spo2_calc ;

*pch_spo2_valid = 1;// float_SPO2 = -45.060*n_ratio_average* n_ratio_average/10000 + 30.354 *n_ratio_average/100 + 94.845 ; // for comparison with table

}

else{

*pn_spo2 = -999 ; // do not use SPO2 since signal an_ratio is out of range

*pch_spo2_valid = 0;

}

}

void maxim_find_peaks( int32_t *pn_locs, int32_t *n_npks, int32_t *pn_x, int32_t n_size, int32_t n_min_height, int32_t n_min_distance, int32_t n_max_num )

/**

* \brief Find peaks

* \par Details

* Find at most MAX_NUM peaks above MIN_HEIGHT separated by at least MIN_DISTANCE

*

* \retval None

*/

{

maxim_peaks_above_min_height( pn_locs, n_npks, pn_x, n_size, n_min_height );

maxim_remove_close_peaks( pn_locs, n_npks, pn_x, n_min_distance );

*n_npks = min( *n_npks, n_max_num );

}

void maxim_peaks_above_min_height( int32_t *pn_locs, int32_t *n_npks, int32_t *pn_x, int32_t n_size, int32_t n_min_height )

/**

* \brief Find peaks above n_min_height

* \par Details

* Find all peaks above MIN_HEIGHT

*

* \retval None

*/

{

int32_t i = 1, n_width;

*n_npks = 0;

while (i < n_size-1){

if (pn_x[i] > n_min_height && pn_x[i] > pn_x[i-1]){ // find left edge of potential peaks

n_width = 1;

while (i+n_width < n_size && pn_x[i] == pn_x[i+n_width]) // find flat peaks

n_width++;

if (pn_x[i] > pn_x[i+n_width] && (*n_npks) < 15 ){ // find right edge of peaks

pn_locs[(*n_npks)++] = i;

// for flat peaks, peak location is left edge

i += n_width+1;

}

else

i += n_width;

}

else

i++;

}

}

void maxim_remove_close_peaks(int32_t *pn_locs, int32_t *pn_npks, int32_t *pn_x, int32_t n_min_distance)

/**

* \brief Remove peaks

* \par Details

* Remove peaks separated by less than MIN_DISTANCE

*

* \retval None

*/

{

int32_t i, j, n_old_npks, n_dist;

/* Order peaks from large to small */

maxim_sort_indices_descend( pn_x, pn_locs, *pn_npks );

for ( i = -1; i < *pn_npks; i++ ){

n_old_npks = *pn_npks;

*pn_npks = i+1;

for ( j = i+1; j < n_old_npks; j++ ){

n_dist = pn_locs[j] - ( i == -1 ? -1 : pn_locs[i] ); // lag-zero peak of autocorr is at index -1

if ( n_dist > n_min_distance || n_dist < -n_min_distance )

pn_locs[(*pn_npks)++] = pn_locs[j];

}

}

// Resort indices int32_to ascending order

maxim_sort_ascend( pn_locs, *pn_npks );

}

void maxim_sort_ascend(int32_t *pn_x, int32_t n_size)

/**

* \brief Sort array

* \par Details

* Sort array in ascending order (insertion sort algorithm)

*

* \retval None

*/

{

int32_t i, j, n_temp;

for (i = 1; i < n_size; i++) {

n_temp = pn_x[i];

for (j = i; j > 0 && n_temp < pn_x[j-1]; j--)

pn_x[j] = pn_x[j-1];

pn_x[j] = n_temp;

}

}

void maxim_sort_indices_descend( int32_t *pn_x, int32_t *pn_indx, int32_t n_size)

/**

* \brief Sort indices

* \par Details

* Sort indices according to descending order (insertion sort algorithm)

*

* \retval None

*/

{

int32_t i, j, n_temp;

for (i = 1; i < n_size; i++) {

n_temp = pn_indx[i];

for (j = i; j > 0 && pn_x[n_temp] > pn_x[pn_indx[j-1]]; j--)

pn_indx[j] = pn_indx[j-1];

pn_indx[j] = n_temp;

}

}