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280 lines
6.8 KiB
C++
280 lines
6.8 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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_output_registers{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0}
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{
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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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{
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for(int p = 0; p < 32; p++)
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{
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switch(c)
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{
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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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{
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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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{
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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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{
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int c = 0;
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while((_master_divider&15) && c < number_of_samples)
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{
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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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{
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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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{\
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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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{
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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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{
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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 < 16 && c < number_of_samples; ic++)
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{
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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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}
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void AY38910::evaluate_output_volume()
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{
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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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// (which is implemented here with reverse logic, assuming _channel_output and _noise_output are already inverted)
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#define level(c, tb, nb) \
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(((((_output_registers[7] >> tb)&1)^1) & _tone_outputs[c]) | ((((_output_registers[7] >> nb)&1)^1) & _noise_output)) ^ 1
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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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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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{
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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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{
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_registers[_selected_register] = value;
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if(_selected_register < 14)
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{
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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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{
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case 0: case 2: case 4:
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case 1: case 3: case 5:
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{
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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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{
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return _registers[_selected_register];
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}
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uint8_t AY38910::get_port_output(bool port_b)
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{
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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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{
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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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{
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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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{
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ControlState new_state;
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switch((int)control_lines)
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{
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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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{
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_control_state = new_state;
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switch(new_state)
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{
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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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