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1 #include <stdlib.h>
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2 #include <stdio.h>
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3 #include <math.h>
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4
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5 /*
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6 Pin Eight standard tuning defines middle C as 2093/8 Hz.
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7 It uses equal temperament: a semitone difference between two pitches
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8 is a factor of 2^(1/12) between their frequencies.
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9 Thus, MIDI 0 = 60, or 2093/256.
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10 */
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11 #define C_IN_OCTAVE(octave) \
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12 ((double)((long int)2093 << octave) / 256.0)
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13 #define TWELFTH_ROOT_OF_TWO 1.0594630943592952645618252949463
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14
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15 /*
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16 DS note frequencies for the tone generator at 8 samples per period
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17 are ((-0x1000000 / (n * 8)))
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18 */
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19 #define FREQ_TO_PSG_PERIOD(freq) \
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20 ((unsigned short)(-0x1000000 / (freq * 8)))
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21
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22
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23 int writePSG(FILE *fp) {
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24
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25 // write header
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26 fputs(".section .rodata\n"
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27 ".balign 4\n"
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28 ".global midi2psgFreq\n"
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29 "midi2psgFreq:", fp);
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30
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31 int octave = 0;
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32
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33 for (; octave < 2; ++octave) {
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34 fprintf(fp, "\n@ unsupported octave %d\n.byte ", octave);
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35 for (int semitone = 0; semitone < 12; ++semitone) {
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36 if (semitone) {
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37 fputs(", ", fp);
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38 }
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39 fputs(" 0, 0", fp);
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40 }
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41 }
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42 for (; octave < 10; ++octave) {
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43 double freq = C_IN_OCTAVE(octave);
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44 fprintf(fp, "\n@ octave %d\n.byte ", octave);
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45 for (int semitone = 0; semitone < 12; ++semitone) {
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46 if (semitone) {
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47 fputs(", ", fp);
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48 freq *= TWELFTH_ROOT_OF_TWO;
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49 }
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50 unsigned int psgFreq = FREQ_TO_PSG_PERIOD(freq);
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51 printf("midi %2d = %.2f = psg %5d\n",
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52 octave * 12 + semitone,
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53 freq,
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54 psgFreq);
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55 fprintf(fp, "%3u,%3u",
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56 psgFreq & 0xFF,
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57 (psgFreq >> 8) & 0xFF);
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58 }
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59 }
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60
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61 fputs("\n", fp);
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62 return 0;
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63 }
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64
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65 /**
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66 * Writes lookup tables used by the ARM7 code.
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67 * Currently, these include the PSG pitch values.
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68 */
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69 int writeARM7(const char *filename) {
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70 FILE *fp = fopen(filename, "wt");
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71 if (!fp) {
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72 return -1;
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73 }
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74 if (writePSG(fp) < 0) {
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75 fclose(fp);
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76 return -1;
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77 }
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78 fclose(fp);
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79 return 0;
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80 }
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81
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82
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83 int main(void) {
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84 if (writeARM7("obj/ds/lookup_tables7.s") < 0) {
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85 return EXIT_FAILURE;
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86 }
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87 return EXIT_SUCCESS;
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88 }
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