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347 lines
11 KiB
C++
347 lines
11 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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#include <cmath>
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using namespace GI::AY38910;
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AY38910::AY38910(Personality personality, Concurrency::DeferringAsyncTaskQueue &task_queue) : task_queue_(task_queue) {
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// Don't use the low bit of the envelope position if this is an AY.
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envelope_position_mask_ |= personality == Personality::AY38910;
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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 < 64; 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: \____ */
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envelope_shapes_[c][p] = (p < 32) ? (p^0x1f) : 0;
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envelope_overflow_masks_[c] = 0x3f;
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break;
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case 4: case 5: case 6: case 7: case 15:
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/* Envelope: /____ */
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envelope_shapes_[c][p] = (p < 32) ? p : 0;
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envelope_overflow_masks_[c] = 0x3f;
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break;
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case 8:
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/* Envelope: \\\\\\\\ */
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envelope_shapes_[c][p] = (p & 0x1f) ^ 0x1f;
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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: //////// */
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envelope_shapes_[c][p] = (p & 0x1f);
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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: \/\/\/\/ */
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envelope_shapes_[c][p] = (p & 0x1f) ^ ((p < 32) ? 0x1f : 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: /\/\/\/\ */
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envelope_shapes_[c][p] = (p & 0x1f) ^ ((p < 32) ? 0x0 : 0x1f);
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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: \------ (if - is high) */
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envelope_shapes_[c][p] = (p < 32) ? (p^0x1f) : 0x1f;
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envelope_overflow_masks_[c] = 0x3f;
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break;
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case 13:
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/* Envelope: /------- */
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envelope_shapes_[c][p] = (p < 32) ? p : 0x1f;
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envelope_overflow_masks_[c] = 0x3f;
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break;
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}
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}
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}
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set_sample_volume_range(0);
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}
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void AY38910::set_sample_volume_range(std::int16_t range) {
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// set up volume lookup table
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const float max_volume = static_cast<float>(range) / 3.0f; // As there are three channels.
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const float root_two = sqrtf(2.0f);
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for(int v = 0; v < 32; v++) {
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volumes_[v] = int(max_volume / powf(root_two, float(v ^ 0x1f) / 2.0f));
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}
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evaluate_output_volume();
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}
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void AY38910::get_samples(std::size_t number_of_samples, int16_t *target) {
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// Note on structure below: the real AY has a built-in divider of 8
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// prior to applying its tone and noise dividers. But the YM fills the
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// same total periods for noise and tone with double-precision envelopes.
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// Therefore this class implements a divider of 4 and doubles the tone
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// and noise periods. The envelope ticks along at the divide-by-four rate,
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// but if this is an AY rather than a YM then its lowest bit is forced to 1,
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// matching the YM datasheet's depiction of envelope level 31 as equal to
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// programmatic volume 15, envelope level 29 as equal to programmatic 14, etc.
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std::size_t c = 0;
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while((master_divider_&3) && 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] << 1;\
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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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// Update 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_ << 1; // To cover the double resolution of envelopes.
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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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// Update 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 the final table position.
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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_ == 64) 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 < 4 && 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_ &= 3;
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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_ | envelope_position_mask_];
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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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// mapped to the range 1–31 in case this is a YM.
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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) << 1) + 1)
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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_ = static_cast<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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bool AY38910::is_zero_level() {
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// Confirm that the AY is trivially at the zero level if all three volume controls are set to fixed zero.
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return output_registers_[0x8] == 0 && output_registers_[0x9] == 0 && output_registers_[0xa] == 0;
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}
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// MARK: - Register manipulation
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void AY38910::select_register(uint8_t r) {
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selected_register_ = r;
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}
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void AY38910::set_register_value(uint8_t value) {
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// There are only 16 registers.
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if(selected_register_ > 15) return;
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// If this is a register that affects audio output, enqueue a mutation onto the
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// audio generation thread.
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if(selected_register_ < 14) {
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const int selected_register = selected_register_;
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task_queue_.defer([=] () {
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// Perform any register-specific mutation to output generation.
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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) | static_cast<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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}
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break;
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case 6:
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noise_period_ = value & 0x1f;
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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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break;
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case 12:
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envelope_period_ = (envelope_period_ & 0xff) | static_cast<int>(value << 8);
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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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// Store a copy of the current register within the storage used by the audio generation
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// thread, and apply any changes to output volume.
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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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// Decide which outputs are going to need updating (if any).
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bool update_port_a = false;
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bool update_port_b = true;
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if(port_handler_) {
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if(selected_register_ == 7) {
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const uint8_t io_change = registers_[7] ^ value;
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update_port_b = !!(io_change&0x80);
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update_port_a = !!(io_change&0x40);
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} else {
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update_port_b = selected_register_ == 15;
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update_port_a = selected_register_ != 15;
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}
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}
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// Keep a copy of the new value that is usable from the emulation thread.
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registers_[selected_register_] = value;
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// Update ports as required.
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if(update_port_b) set_port_output(true);
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if(update_port_a) set_port_output(false);
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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 0s
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// when read, conforming to CPC-sourced unit tests.
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const uint8_t register_masks[16] = {
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0xff, 0x0f, 0xff, 0x0f, 0xff, 0x0f, 0x1f, 0xff,
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0x1f, 0x1f, 0x1f, 0xff, 0xff, 0x0f, 0xff, 0xff
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};
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if(selected_register_ > 15) return 0xff;
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return registers_[selected_register_] & register_masks[selected_register_];
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}
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// MARK: - Port querying
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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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// MARK: - Bus handling
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void AY38910::set_port_handler(PortHandler *handler) {
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port_handler_ = handler;
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set_port_output(true);
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set_port_output(false);
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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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update_bus();
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}
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void AY38910::set_port_output(bool port_b) {
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// Per the data sheet: "each [IO] pin is provided with an on-chip pull-up resistor,
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// so that when in the "input" mode, all pins will read normally high". Therefore,
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// report programmer selection of input mode as creating an output of 0xff.
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if(port_handler_) {
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const bool is_output = !!(registers_[7] & (port_b ? 0x80 : 0x40));
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port_handler_->set_port_output(port_b, is_output ? registers_[port_b ? 15 : 14] : 0xff);
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}
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}
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uint8_t AY38910::get_data_output() {
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if(control_state_ == Read && selected_register_ >= 14 && selected_register_ < 16) {
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// Per http://cpctech.cpc-live.com/docs/psgnotes.htm if a port is defined as output then the
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// value returned to the CPU when reading it is the and of the output value and any input.
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// If it's defined as input then you just get the input.
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const uint8_t mask = port_handler_ ? port_handler_->get_port_input(selected_register_ == 15) : 0xff;
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switch(selected_register_) {
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default: break;
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case 14: return mask & ((registers_[0x7] & 0x40) ? registers_[14] : 0xff);
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case 15: return mask & ((registers_[0x7] & 0x80) ? registers_[15] : 0xff);
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}
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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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switch(static_cast<int>(control_lines)) {
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default: control_state_ = Inactive; break;
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case static_cast<int>(BDIR | BC2 | BC1):
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case BDIR:
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case BC1: control_state_ = LatchAddress; break;
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case static_cast<int>(BC2 | BC1): control_state_ = Read; break;
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case static_cast<int>(BDIR | BC2): control_state_ = Write; break;
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}
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update_bus();
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}
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void AY38910::update_bus() {
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// Assume no output, unless this turns out to be a read.
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data_output_ = 0xff;
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switch(control_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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