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annotate psg.c @ 354:15dd6418fe67

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Initial PSG support. Mostly works, noise channel is borked though.
author Mike Pavone <pavone@retrodev.com>
date Thu, 23 May 2013 23:42:42 -0700
parents
children fcd31d19dddd
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rev   line source
354
15dd6418fe67 Initial PSG support. Mostly works, noise channel is borked though.
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1 #include "psg.h"
15dd6418fe67 Initial PSG support. Mostly works, noise channel is borked though.
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2 #include "render.h"
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3 #include <string.h>
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4 #include <stdlib.h>
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5
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6 void psg_init(psg_context * context, uint32_t sample_rate, uint32_t clock_rate, uint32_t samples_frame)
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7 {
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8 memset(context, 0, sizeof(*context));
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9 context->audio_buffer = malloc(sizeof(*context->audio_buffer) * samples_frame);
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10 context->back_buffer = malloc(sizeof(*context->audio_buffer) * samples_frame);
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11 context->buffer_inc = (double)sample_rate / (double)clock_rate;
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12 context->samples_frame = samples_frame;
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13 for (int i = 0; i < 4; i++) {
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14 context->volume[i] = 0xF;
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15 }
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16 }
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17
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18 void psg_write(psg_context * context, uint8_t value)
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19 {
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20 if (value & 0x80) {
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21 context->latch = value & 0x70;
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22 uint8_t channel = value >> 5 & 0x3;
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23 if (value & 0x10) {
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24 context->volume[channel] = value & 0xF;
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25 } else {
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26 if (channel == 3) {
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27 switch(value & 0x3)
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28 {
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29 case 0:
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30 case 1:
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31 case 2:
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32 context->counter_load[3] = 0x10 << (value & 0x3);
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33 context->noise_use_tone = 0;
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34 break;
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35 default:
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36 context->counter_load[3] = context->counter_load[2];
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37 context->noise_use_tone = 1;
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38 }
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39 context->noise_type = value & 0x4;
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40 context->lsfr = 0x8000;
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41 } else {
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42 context->counter_load[channel] = (context->counter_load[channel] & 0x3F0) | (value & 0xF);
15dd6418fe67 Initial PSG support. Mostly works, noise channel is borked though.
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43 if (channel == 2 && context->noise_use_tone) {
15dd6418fe67 Initial PSG support. Mostly works, noise channel is borked though.
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44 context->counter_load[3] = context->counter_load[2];
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45 }
15dd6418fe67 Initial PSG support. Mostly works, noise channel is borked though.
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46 }
15dd6418fe67 Initial PSG support. Mostly works, noise channel is borked though.
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47 }
15dd6418fe67 Initial PSG support. Mostly works, noise channel is borked though.
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48 } else {
15dd6418fe67 Initial PSG support. Mostly works, noise channel is borked though.
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49 if (!(context->latch & 0x10)) {
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50 uint8_t channel = context->latch >> 5 & 0x3;
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51 if (channel != 3) {
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52 context->counter_load[channel] = (value << 4 & 0x3F0) | (context->counter_load[channel] & 0xF);
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53 if (channel == 2 && context->noise_use_tone) {
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54 context->counter_load[3] = context->counter_load[2];
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55 }
15dd6418fe67 Initial PSG support. Mostly works, noise channel is borked though.
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56 }
15dd6418fe67 Initial PSG support. Mostly works, noise channel is borked though.
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57 }
15dd6418fe67 Initial PSG support. Mostly works, noise channel is borked though.
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58 }
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59 }
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60
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61 #define PSG_VOL_DIV 2
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62
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63 //table shamelessly swiped from PSG doc from smspower.org
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64 int16_t volume_table[16] = {
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65 32767/PSG_VOL_DIV, 26028/PSG_VOL_DIV, 20675/PSG_VOL_DIV, 16422/PSG_VOL_DIV, 13045/PSG_VOL_DIV, 10362/PSG_VOL_DIV,
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66 8231/PSG_VOL_DIV, 6568/PSG_VOL_DIV, 5193/PSG_VOL_DIV, 4125/PSG_VOL_DIV, 3277/PSG_VOL_DIV, 2603/PSG_VOL_DIV,
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67 2067/PSG_VOL_DIV, 1642/PSG_VOL_DIV, 1304/PSG_VOL_DIV, 0
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68 };
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69
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70 void psg_run(psg_context * context, uint32_t cycles)
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71 {
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72 while (context->cycles < cycles) {
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73 for (int i = 0; i < 4; i++) {
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74 if (context->counters[i]) {
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75 context->counters[i] -= 1;
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76 }
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77 if (!context->counters[i]) {
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78 context->counters[i] = context->counter_load[i];
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79 context->output_state[i] = !context->output_state[i];
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80 if (i == 3 && context->output_state[i]) {
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81 context->noise_out = context->lsfr & 1;
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82 context->lsfr = (context->lsfr >> 1) | (context->lsfr << 15);
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83 if (context->noise_type) {
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84 //white noise
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85 if (context->lsfr & 0x40) {
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86 context->lsfr ^= 0x8000;
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87 }
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88 }
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89 }
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90 }
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91 }
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92 context->buffer_fraction += context->buffer_inc;
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93 if (context->buffer_fraction >= 1.0) {
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94 context->buffer_fraction -= 1.0;
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95 int16_t acc = 0;
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96 for (int i = 0; i < 3; i++) {
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97 if (context->output_state[i]) {
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98 acc += volume_table[context->volume[i]];
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99 }
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100 }
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101 if (context->noise_out) {
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102 acc += volume_table[context->volume[3]];
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103 }
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104 context->audio_buffer[context->buffer_pos++] = acc;
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105 if (context->buffer_pos == context->samples_frame) {
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106 render_wait_audio(context);
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107 }
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108 }
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109 context->cycles++;
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110 }
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111 }
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112