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annotate fir/freqresp.c @ 376:9b3e5be96bab

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fir2freq: a tool for analyzing captured FIR coefficient sets
author Mychaela Falconia <falcon@freecalypso.org>
date Mon, 02 Aug 2021 04:59:46 +0000
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9b3e5be96bab fir2freq: a tool for analyzing captured FIR coefficient sets
Mychaela Falconia <falcon@freecalypso.org>
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1 /*
9b3e5be96bab fir2freq: a tool for analyzing captured FIR coefficient sets
Mychaela Falconia <falcon@freecalypso.org>
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2 * This program computes the frequency response of a Calypso DSP FIR filter
9b3e5be96bab fir2freq: a tool for analyzing captured FIR coefficient sets
Mychaela Falconia <falcon@freecalypso.org>
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3 * whose coefficients have been captured somewhere out in the wild.
9b3e5be96bab fir2freq: a tool for analyzing captured FIR coefficient sets
Mychaela Falconia <falcon@freecalypso.org>
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4 * The math has been taken from section 2.2.2 of this article:
9b3e5be96bab fir2freq: a tool for analyzing captured FIR coefficient sets
Mychaela Falconia <falcon@freecalypso.org>
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5 *
9b3e5be96bab fir2freq: a tool for analyzing captured FIR coefficient sets
Mychaela Falconia <falcon@freecalypso.org>
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6 * https://dspguru.com/dsp/faqs/fir/properties/
9b3e5be96bab fir2freq: a tool for analyzing captured FIR coefficient sets
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7 */
9b3e5be96bab fir2freq: a tool for analyzing captured FIR coefficient sets
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8
9b3e5be96bab fir2freq: a tool for analyzing captured FIR coefficient sets
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9 #include <math.h>
9b3e5be96bab fir2freq: a tool for analyzing captured FIR coefficient sets
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10 #include <stdio.h>
9b3e5be96bab fir2freq: a tool for analyzing captured FIR coefficient sets
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11 #include <stdlib.h>
9b3e5be96bab fir2freq: a tool for analyzing captured FIR coefficient sets
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12
9b3e5be96bab fir2freq: a tool for analyzing captured FIR coefficient sets
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13 #define NCOEFF 31
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14
9b3e5be96bab fir2freq: a tool for analyzing captured FIR coefficient sets
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15 int coeff_int[NCOEFF];
9b3e5be96bab fir2freq: a tool for analyzing captured FIR coefficient sets
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16 float coeff_float[NCOEFF];
9b3e5be96bab fir2freq: a tool for analyzing captured FIR coefficient sets
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17 unsigned nsteps;
9b3e5be96bab fir2freq: a tool for analyzing captured FIR coefficient sets
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18 float freq_step, omega_step;
9b3e5be96bab fir2freq: a tool for analyzing captured FIR coefficient sets
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19 float freq, omega;
9b3e5be96bab fir2freq: a tool for analyzing captured FIR coefficient sets
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20
9b3e5be96bab fir2freq: a tool for analyzing captured FIR coefficient sets
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21 static void
9b3e5be96bab fir2freq: a tool for analyzing captured FIR coefficient sets
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22 coeff_to_float()
9b3e5be96bab fir2freq: a tool for analyzing captured FIR coefficient sets
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23 {
9b3e5be96bab fir2freq: a tool for analyzing captured FIR coefficient sets
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24 unsigned n;
9b3e5be96bab fir2freq: a tool for analyzing captured FIR coefficient sets
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25
9b3e5be96bab fir2freq: a tool for analyzing captured FIR coefficient sets
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26 for (n = 0; n < NCOEFF; n++)
9b3e5be96bab fir2freq: a tool for analyzing captured FIR coefficient sets
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27 coeff_float[n] = coeff_int[n] / 16384.0f;
9b3e5be96bab fir2freq: a tool for analyzing captured FIR coefficient sets
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28 }
9b3e5be96bab fir2freq: a tool for analyzing captured FIR coefficient sets
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29
9b3e5be96bab fir2freq: a tool for analyzing captured FIR coefficient sets
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30 static void
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31 do_one_freq()
9b3e5be96bab fir2freq: a tool for analyzing captured FIR coefficient sets
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32 {
9b3e5be96bab fir2freq: a tool for analyzing captured FIR coefficient sets
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33 unsigned n;
9b3e5be96bab fir2freq: a tool for analyzing captured FIR coefficient sets
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34 float angle_arg, rsum, isum;
9b3e5be96bab fir2freq: a tool for analyzing captured FIR coefficient sets
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35 float gain, db;
9b3e5be96bab fir2freq: a tool for analyzing captured FIR coefficient sets
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36
9b3e5be96bab fir2freq: a tool for analyzing captured FIR coefficient sets
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37 angle_arg = 0;
9b3e5be96bab fir2freq: a tool for analyzing captured FIR coefficient sets
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38 rsum = 0;
9b3e5be96bab fir2freq: a tool for analyzing captured FIR coefficient sets
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39 isum = 0;
9b3e5be96bab fir2freq: a tool for analyzing captured FIR coefficient sets
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40 for (n = 0; n < NCOEFF; n++) {
9b3e5be96bab fir2freq: a tool for analyzing captured FIR coefficient sets
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41 rsum += coeff_float[n] * cosf(angle_arg);
9b3e5be96bab fir2freq: a tool for analyzing captured FIR coefficient sets
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42 isum -= coeff_float[n] * sinf(angle_arg);
9b3e5be96bab fir2freq: a tool for analyzing captured FIR coefficient sets
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43 angle_arg += omega;
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44 }
9b3e5be96bab fir2freq: a tool for analyzing captured FIR coefficient sets
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45 gain = hypotf(rsum, isum);
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46 db = log10f(gain) * 20.0f;
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47 printf("%.2f\t%f\t%.2f\n", freq, gain, db);
9b3e5be96bab fir2freq: a tool for analyzing captured FIR coefficient sets
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48 }
9b3e5be96bab fir2freq: a tool for analyzing captured FIR coefficient sets
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49
9b3e5be96bab fir2freq: a tool for analyzing captured FIR coefficient sets
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50 main(argc, argv)
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51 char **argv;
9b3e5be96bab fir2freq: a tool for analyzing captured FIR coefficient sets
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52 {
9b3e5be96bab fir2freq: a tool for analyzing captured FIR coefficient sets
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53 unsigned n;
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54
9b3e5be96bab fir2freq: a tool for analyzing captured FIR coefficient sets
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55 if (argc != 3) {
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56 fprintf(stderr, "usage: %s coeff-file nsteps\n", argv[0]);
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57 exit(1);
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58 }
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59 if (read_fir_coeff_table_int(argv[1], coeff_int) < 0)
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60 exit(1); /* error msg already printed */
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61 coeff_to_float();
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62 nsteps = strtoul(argv[2], 0, 0);
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63 if (nsteps < 1) {
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64 fprintf(stderr, "error: nsteps argument must be >= 1\n");
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65 exit(1);
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66 }
9b3e5be96bab fir2freq: a tool for analyzing captured FIR coefficient sets
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67 freq_step = 4000.0f / nsteps;
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68 omega_step = M_PI / nsteps;
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69 n = 0;
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70 freq = 0;
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71 omega = 0;
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72 for (;;) {
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73 do_one_freq();
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74 if (n >= nsteps)
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75 break;
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76 n++;
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77 freq += freq_step;
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78 omega += omega_step;
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79 }
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80 exit(0);
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81 }