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265 lines
7.4 KiB
C++
265 lines
7.4 KiB
C++
//
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// AY-3-8910.cpp
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// Clock Signal
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//
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// Created by Thomas Harte on 14/10/2016.
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// Copyright © 2016 Thomas Harte. All rights reserved.
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//
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#include "AY38910.hpp"
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using namespace GI;
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AY38910::AY38910() :
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selected_register_(0),
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tone_counters_{0, 0, 0}, tone_periods_{0, 0, 0}, tone_outputs_{0, 0, 0},
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noise_shift_register_(0xffff), noise_period_(0), noise_counter_(0), noise_output_(0),
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envelope_divider_(0), envelope_period_(0), envelope_position_(0),
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master_divider_(0),
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output_registers_{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0} {
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output_registers_[8] = output_registers_[9] = output_registers_[10] = 0;
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// set up envelope lookup tables
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for(int c = 0; c < 16; c++) {
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for(int p = 0; p < 32; p++) {
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switch(c) {
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case 0: case 1: case 2: case 3: case 9:
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envelope_shapes_[c][p] = (p < 16) ? (p^0xf) : 0;
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envelope_overflow_masks_[c] = 0x1f;
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break;
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case 4: case 5: case 6: case 7: case 15:
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envelope_shapes_[c][p] = (p < 16) ? p : 0;
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envelope_overflow_masks_[c] = 0x1f;
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break;
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case 8:
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envelope_shapes_[c][p] = (p & 0xf) ^ 0xf;
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envelope_overflow_masks_[c] = 0x00;
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break;
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case 12:
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envelope_shapes_[c][p] = (p & 0xf);
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envelope_overflow_masks_[c] = 0x00;
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break;
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case 10:
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envelope_shapes_[c][p] = (p & 0xf) ^ ((p < 16) ? 0xf : 0x0);
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envelope_overflow_masks_[c] = 0x00;
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break;
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case 14:
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envelope_shapes_[c][p] = (p & 0xf) ^ ((p < 16) ? 0x0 : 0xf);
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envelope_overflow_masks_[c] = 0x00;
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break;
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case 11:
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envelope_shapes_[c][p] = (p < 16) ? (p^0xf) : 0xf;
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envelope_overflow_masks_[c] = 0x1f;
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break;
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case 13:
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envelope_shapes_[c][p] = (p < 16) ? p : 0xf;
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envelope_overflow_masks_[c] = 0x1f;
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break;
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}
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}
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}
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// set up volume lookup table
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float max_volume = 8192;
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float root_two = sqrtf(2.0f);
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for(int v = 0; v < 16; v++) {
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volumes_[v] = (int)(max_volume / powf(root_two, (float)(v ^ 0xf)));
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}
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volumes_[0] = 0;
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}
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void AY38910::set_clock_rate(double clock_rate) {
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set_input_rate((float)clock_rate);
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}
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void AY38910::get_samples(unsigned int number_of_samples, int16_t *target) {
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unsigned int c = 0;
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while((master_divider_&7) && c < number_of_samples) {
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target[c] = output_volume_;
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master_divider_++;
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c++;
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}
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while(c < number_of_samples) {
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#define step_channel(c) \
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if(tone_counters_[c]) tone_counters_[c]--;\
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else {\
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tone_outputs_[c] ^= 1;\
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tone_counters_[c] = tone_periods_[c];\
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}
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// update the tone channels
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step_channel(0);
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step_channel(1);
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step_channel(2);
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#undef step_channel
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// ... the noise generator. This recomputes the new bit repeatedly but harmlessly, only shifting
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// it into the official 17 upon divider underflow.
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if(noise_counter_) noise_counter_--;
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else {
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noise_counter_ = noise_period_;
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noise_output_ ^= noise_shift_register_&1;
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noise_shift_register_ |= ((noise_shift_register_ ^ (noise_shift_register_ >> 3))&1) << 17;
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noise_shift_register_ >>= 1;
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}
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// ... and the envelope generator. Table based for pattern lookup, with a 'refill' step — a way of
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// implementing non-repeating patterns by locking them to table position 0x1f.
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if(envelope_divider_) envelope_divider_--;
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else {
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envelope_divider_ = envelope_period_;
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envelope_position_ ++;
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if(envelope_position_ == 32) envelope_position_ = envelope_overflow_masks_[output_registers_[13]];
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}
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evaluate_output_volume();
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for(int ic = 0; ic < 8 && c < number_of_samples; ic++) {
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target[c] = output_volume_;
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c++;
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master_divider_++;
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}
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}
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master_divider_ &= 7;
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}
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void AY38910::evaluate_output_volume() {
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int envelope_volume = envelope_shapes_[output_registers_[13]][envelope_position_];
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// The output level for a channel is:
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// 1 if neither tone nor noise is enabled;
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// 0 if either tone or noise is enabled and its value is low.
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// The tone/noise enable bits use inverse logic — 0 = on, 1 = off — permitting the OR logic below.
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#define tone_level(c, tone_bit) (tone_outputs_[c] | (output_registers_[7] >> tone_bit))
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#define noise_level(c, noise_bit) (noise_output_ | (output_registers_[7] >> noise_bit))
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#define level(c, tone_bit, noise_bit) tone_level(c, tone_bit) & noise_level(c, noise_bit) & 1
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const int channel_levels[3] = {
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level(0, 0, 3),
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level(1, 1, 4),
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level(2, 2, 5),
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};
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#undef level
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// Channel volume is a simple selection: if the bit at 0x10 is set, use the envelope volume; otherwise use the lower four bits
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#define channel_volume(c) \
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((output_registers_[c] >> 4)&1) * envelope_volume + (((output_registers_[c] >> 4)&1)^1) * (output_registers_[c]&0xf)
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const int volumes[3] = {
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channel_volume(8),
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channel_volume(9),
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channel_volume(10)
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};
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#undef channel_volume
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// Mix additively.
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output_volume_ = (int16_t)(
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volumes_[volumes[0]] * channel_levels[0] +
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volumes_[volumes[1]] * channel_levels[1] +
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volumes_[volumes[2]] * channel_levels[2]
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);
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}
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void AY38910::select_register(uint8_t r) {
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selected_register_ = r & 0xf;
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}
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void AY38910::set_register_value(uint8_t value) {
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registers_[selected_register_] = value;
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if(selected_register_ < 14) {
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int selected_register = selected_register_;
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enqueue([=] () {
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uint8_t masked_value = value;
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switch(selected_register) {
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case 0: case 2: case 4:
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case 1: case 3: case 5: {
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int channel = selected_register >> 1;
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if(selected_register & 1)
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tone_periods_[channel] = (tone_periods_[channel] & 0xff) | (uint16_t)((value&0xf) << 8);
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else
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tone_periods_[channel] = (tone_periods_[channel] & ~0xff) | value;
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tone_counters_[channel] = tone_periods_[channel];
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}
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break;
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case 6:
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noise_period_ = value & 0x1f;
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noise_counter_ = noise_period_;
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break;
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case 11:
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envelope_period_ = (envelope_period_ & ~0xff) | value;
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envelope_divider_ = envelope_period_;
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break;
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case 12:
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envelope_period_ = (envelope_period_ & 0xff) | (int)(value << 8);
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envelope_divider_ = envelope_period_;
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break;
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case 13:
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masked_value &= 0xf;
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envelope_position_ = 0;
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break;
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}
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output_registers_[selected_register] = masked_value;
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evaluate_output_volume();
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});
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}
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}
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uint8_t AY38910::get_register_value() {
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// This table ensures that bits that aren't defined within the AY are returned as 1s
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// when read. I can't find documentation on this and don't have a machine to test, so
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// this is provisionally a guess. TODO: investigate.
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const uint8_t register_masks[16] = {
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0x00, 0xf0, 0x00, 0xf0, 0x00, 0xf0, 0xe0, 0x00,
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0xe0, 0xe0, 0xe0, 0x00, 0x00, 0xf0, 0x00, 0x00
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};
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return registers_[selected_register_] | register_masks[selected_register_];
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}
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uint8_t AY38910::get_port_output(bool port_b) {
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return registers_[port_b ? 15 : 14];
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}
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void AY38910::set_data_input(uint8_t r) {
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data_input_ = r;
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}
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uint8_t AY38910::get_data_output() {
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return data_output_;
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}
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void AY38910::set_control_lines(ControlLines control_lines) {
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ControlState new_state;
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switch((int)control_lines) {
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default: new_state = Inactive; break;
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case (int)(BCDIR | BC2 | BC1):
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case BCDIR:
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case BC1: new_state = LatchAddress; break;
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case (int)(BC2 | BC1): new_state = Read; break;
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case (int)(BCDIR | BC2): new_state = Write; break;
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}
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if(new_state != control_state_) {
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control_state_ = new_state;
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switch(new_state) {
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default: break;
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case LatchAddress: select_register(data_input_); break;
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case Write: set_register_value(data_input_); break;
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case Read: data_output_ = get_register_value(); break;
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}
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}
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}
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