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Starts trying to make sense of the various fields at play.

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Thomas Harte 2020-04-08 23:15:44 -04:00
parent dd6769bfbc
commit a0d14f4030
2 changed files with 47 additions and 6 deletions
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8
Components/OPL2/OPL2.cpp
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@ -185,7 +185,7 @@ void OPLL::write_register(uint8_t address, uint8_t value) {
if(address >= 0x20 && address <= 0x28) {
const auto index = address - 0x20;
channels_[index].frequency = (channels_[index].frequency & 0xff) | (value & 1);
channels_[index].octave = (value >> 1) & 7;
channels_[index].octave = (value >> 1) & 0x7;
channels_[index].key_on = value & 0x10;
channels_[index].hold_sustain_level = value & 0x20;
return;
@ -198,8 +198,8 @@ void OPLL::setup_fixed_instrument(int number, const uint8_t *data) {
auto carrier = &operators_[number * 2 + 1];
// Set waveforms — only sine and halfsine are available.
carrier->waveform = (data[3] & 0x10) ? 1 : 0;
modulator->waveform = (data[3] & 0x08) ? 1 : 0;
carrier->waveform = Operator::Waveform((data[3] & 0x10) ? 1 : 0);
modulator->waveform = Operator::Waveform((data[3] & 0x08) ? 1 : 0);
// Set modulator amplitude and key-scale level.
modulator->scaling_level = data[2] >> 6;
@ -317,7 +317,7 @@ void OPL2::write_register(uint8_t address, uint8_t value) {
const auto index = operator_by_address[address - 0xe0];
if(index == -1) return;
operators_[index].waveform = value & 3;
operators_[index].waveform = Operator::Waveform(value & 3);
return;
}

45
Components/OPL2/OPL2.hpp
View File

@ -19,18 +19,43 @@ namespace Yamaha {
namespace OPL {
struct Operator {
/// If true then an amplitude modulation of "3.7Hz" is applied,
/// with a depth "determined by the AM-DEPTH of the BD register"?
bool apply_amplitude_modulation = false;
/// If true then a vibrato of '6.4 Hz' is applied, with a depth
/// "determined by VOB_DEPTH of the BD register"?
bool apply_vibrato = false;
/// Selects between an ADSR envelope that holds at the sustain level
/// for as long as this key is on, releasing afterwards, and one that
/// simply switches straight to the release rate once the sustain
/// level is hit, getting back to 0 regardless of an ongoing key-on.
bool hold_sustain_level = false;
/// Provides a potential faster step through the ADSR envelope. Cf. p12.
bool keyboard_scaling_rate = false;
/// Indexes a lookup table to determine what multiple of the channel's frequency
/// this operator is advancing at.
int frequency_multiple = 0;
int scaling_level = 0;
/// Sets the current output level of this modulator, as an attenuation.
int output_level = 0;
/// Selects attenuation that is applied as a function of interval. Cf. p14.
int scaling_level = 0;
/// Sets the ADSR rates.
int attack_rate = 0;
int decay_rate = 0;
int sustain_level = 0;
int release_rate = 0;
int waveform = 0;
/// Selects the generated waveform.
enum class Waveform {
Sine, HalfSine, AbsSine, PulseSine
} waveform = Waveform::Sine;
};
struct Channel {
@ -39,6 +64,22 @@ struct Channel {
bool key_on = false;
int feedback_strength = 0;
bool use_fm_synthesis = true;
// This should be called at a rate of around 49,716 Hz.
void update() {
// Per the documentation:
// F-Num = Music Frequency * 2^(20-Block) / 49716
//
// Given that a 256-entry table is used to store a quarter of a sine wave,
// making 1024 steps per complete wave, add what I've called frequency
// to an accumulator and move on whenever that exceeds 2^(10 - octave).
//
// TODO: but, how does that apply to the two operator multipliers?
//
// Or: 2^19?
}
// Stateful information.
};
template <typename Child> class OPLBase: public ::Outputs::Speaker::SampleSource {