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Introduces double-resolution envelopes for the Atari ST.
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Thomas Harte
parent
d85ae21b2f
commit
206ab380c7
@ -13,44 +13,55 @@
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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 < 32; p++) {
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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_shapes_[c][p] = (p < 16) ? (p^0xf) : 0;
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envelope_overflow_masks_[c] = 0x1f;
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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_shapes_[c][p] = (p < 16) ? p : 0;
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envelope_overflow_masks_[c] = 0x1f;
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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_shapes_[c][p] = (p & 0xf) ^ 0xf;
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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_shapes_[c][p] = (p & 0xf);
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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_shapes_[c][p] = (p & 0xf) ^ ((p < 16) ? 0xf : 0x0);
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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_shapes_[c][p] = (p & 0xf) ^ ((p < 16) ? 0x0 : 0xf);
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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_shapes_[c][p] = (p < 16) ? (p^0xf) : 0xf;
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envelope_overflow_masks_[c] = 0x1f;
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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_shapes_[c][p] = (p < 16) ? p : 0xf;
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envelope_overflow_masks_[c] = 0x1f;
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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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@ -63,16 +74,24 @@ 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 < 16; v++) {
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volumes_[v] = static_cast<int>(max_volume / powf(root_two, static_cast<float>(v ^ 0xf)));
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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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volumes_[0] = 0;
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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_&7) && c < number_of_samples) {
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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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@ -83,49 +102,49 @@ void AY38910::get_samples(std::size_t number_of_samples, int16_t *target) {
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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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tone_counters_[c] = tone_periods_[c] << 1;\
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}
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// update the tone channels
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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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// 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_;
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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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// ... 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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// 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_ == 32) envelope_position_ = envelope_overflow_masks_[output_registers_[13]];
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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 < 8 && c < number_of_samples; ic++) {
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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_ &= 7;
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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_];
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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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@ -142,9 +161,10 @@ void AY38910::evaluate_output_volume() {
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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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// 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)
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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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@ -116,11 +116,11 @@ class AY38910: public ::Outputs::Speaker::SampleSource {
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int envelope_period_ = 0;
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int envelope_divider_ = 0;
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int envelope_position_ = 0;
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int envelope_shapes_[16][32];
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int envelope_position_ = 0, envelope_position_mask_ = 0;
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int envelope_shapes_[16][64];
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int envelope_overflow_masks_[16];
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int volumes_[16];
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int volumes_[32];
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enum ControlState {
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Inactive,
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