CLK/Components/AY38910/AY38910.cpp

//
//  AY-3-8910.cpp
//  Clock Signal
//
//  Created by Thomas Harte on 14/10/2016.
//  Copyright © 2016 Thomas Harte. All rights reserved.
//

#include "AY38910.hpp"

using namespace GI;

AY38910::AY38910() :
	_selected_register(0),
	_tone_counters{0, 0, 0}, _tone_periods{0, 0, 0}, _tone_outputs{0, 0, 0},
	_noise_shift_register(0xffff), _noise_period(0), _noise_counter(0), _noise_output(0),
	_envelope_divider(0), _envelope_period(0), _envelope_position(0),
	_master_divider(0),
	_output_registers{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0}
{
	_output_registers[8] = _output_registers[9] = _output_registers[10] = 0;

	// set up envelope lookup tables
	for(int c = 0; c < 16; c++)
	{
		for(int p = 0; p < 32; p++)
		{
			switch(c)
			{
				case 0: case 1: case 2: case 3: case 9:
					_envelope_shapes[c][p] = (p < 16) ? (p^0xf) : 0;
					_envelope_overflow_masks[c] = 0x1f;
				break;
				case 4: case 5: case 6: case 7: case 15:
					_envelope_shapes[c][p] = (p < 16) ? p : 0;
					_envelope_overflow_masks[c] = 0x1f;
				break;

				case 8:
					_envelope_shapes[c][p] = (p & 0xf) ^ 0xf;
					_envelope_overflow_masks[c] = 0x00;
				break;
				case 12:
					_envelope_shapes[c][p] = (p & 0xf);
					_envelope_overflow_masks[c] = 0x00;
				break;

				case 10:
					_envelope_shapes[c][p] = (p & 0xf) ^ ((p < 16) ? 0xf : 0x0);
					_envelope_overflow_masks[c] = 0x00;
				break;
				case 14:
					_envelope_shapes[c][p] = (p & 0xf) ^ ((p < 16) ? 0x0 : 0xf);
					_envelope_overflow_masks[c] = 0x00;
				break;

				case 11:
					_envelope_shapes[c][p] = (p < 16) ? (p^0xf) : 0xf;
					_envelope_overflow_masks[c] = 0x1f;
				break;
				case 13:
					_envelope_shapes[c][p] = (p < 16) ? p : 0xf;
					_envelope_overflow_masks[c] = 0x1f;
				break;
			}
		}
	}

	// set up volume lookup table
	float max_volume = 8192;
	float root_two = sqrtf(2.0f);
	for(int v = 0; v < 16; v++)
	{
		_volumes[v] = (int)(max_volume / powf(root_two, (float)(v ^ 0xf)));
	}
	_volumes[0] = 0;
}

void AY38910::set_clock_rate(double clock_rate)
{
	set_input_rate((float)clock_rate);
}

void AY38910::get_samples(unsigned int number_of_samples, int16_t *target)
{
	int c = 0;
	while((_master_divider&15) && c < number_of_samples)
	{
		target[c] = _output_volume;
		_master_divider++;
		c++;
	}

	while(c < number_of_samples)
	{
#define step_channel(c) \
	if(_tone_counters[c]) _tone_counters[c]--;\
	else\
	{\
		_tone_outputs[c] ^= 1;\
		_tone_counters[c] = _tone_periods[c];\
	}

		// update the tone channels
		step_channel(0);
		step_channel(1);
		step_channel(2);

#undef step_channel

		// ... the noise generator. This recomputes the new bit repeatedly but harmlessly, only shifting
		// it into the official 17 upon divider underflow.
		if(_noise_counter) _noise_counter--;
		else
		{
			_noise_counter = _noise_period;
			_noise_output ^= _noise_shift_register&1;
			_noise_shift_register |= ((_noise_shift_register ^ (_noise_shift_register >> 3))&1) << 17;
			_noise_shift_register >>= 1;
		}

		// ... and the envelope generator. Table based for pattern lookup, with a 'refill' step — a way of
		// implementing non-repeating patterns by locking them to table position 0x1f.
		if(_envelope_divider) _envelope_divider--;
		else
		{
			_envelope_divider = _envelope_period;
			_envelope_position ++;
			if(_envelope_position == 32) _envelope_position = _envelope_overflow_masks[_output_registers[13]];
		}

		evaluate_output_volume();

		for(int ic = 0; ic < 16 && c < number_of_samples; ic++)
		{
			target[c] = _output_volume;
			c++;
			_master_divider++;
		}
	}

	_master_divider &= 15;
}

void AY38910::evaluate_output_volume()
{
	int envelope_volume = _envelope_shapes[_output_registers[13]][_envelope_position];

	// The output level for a channel is:
	//	1 if neither tone nor noise is enabled;
	//	0 if either tone or noise is enabled and its value is low.
	// The tone/noise enable bits use inverse logic — 0 = on, 1 = off — permitting the OR logic below.
#define tone_level(c, tone_bit)		(_tone_outputs[c] | (_output_registers[7] >> tone_bit))
#define noise_level(c, noise_bit)	(_noise_output | (_output_registers[7] >> noise_bit))

#define level(c, tone_bit, noise_bit)	tone_level(c, tone_bit) & noise_level(c, noise_bit) & 1
	const int channel_levels[3] = {
		level(0, 0, 3),
		level(1, 1, 4),
		level(2, 2, 5),
	};
#undef level

		// Channel volume is a simple selection: if the bit at 0x10 is set, use the envelope volume; otherwise use the lower four bits
#define channel_volume(c)	\
	((_output_registers[c] >> 4)&1) * envelope_volume + (((_output_registers[c] >> 4)&1)^1) * (_output_registers[c]&0xf)

	const int volumes[3] = {
		channel_volume(8),
		channel_volume(9),
		channel_volume(10)
	};
#undef channel_volume

	// Mix additively.
	_output_volume = (int16_t)(
		_volumes[volumes[0]] * channel_levels[0] +
		_volumes[volumes[1]] * channel_levels[1] +
		_volumes[volumes[2]] * channel_levels[2]
	);
}

void AY38910::select_register(uint8_t r)
{
	_selected_register = r & 0xf;
}

void AY38910::set_register_value(uint8_t value)
{
	_registers[_selected_register] = value;
	if(_selected_register < 14)
	{
		int selected_register = _selected_register;
		enqueue([=] () {
			uint8_t masked_value = value;
			switch(selected_register)
			{
				case 0: case 2: case 4:
				case 1: case 3: case 5:
				{
					int channel = selected_register >> 1;

					if(selected_register & 1)
						_tone_periods[channel] = (_tone_periods[channel] & 0xff) | (uint16_t)((value&0xf) << 8);
					else
						_tone_periods[channel] = (_tone_periods[channel] & ~0xff) | value;
					_tone_counters[channel] = _tone_periods[channel];
				}
				break;

				case 6:
					_noise_period = value & 0x1f;
					_noise_counter = _noise_period;
				break;

				case 11:
					_envelope_period = (_envelope_period & ~0xff) | value;
					_envelope_divider = _envelope_period;
				break;

				case 12:
					_envelope_period = (_envelope_period & 0xff) | (int)(value << 8);
					_envelope_divider = _envelope_period;
				break;

				case 13:
					masked_value &= 0xf;
					_envelope_position = 0;
				break;
			}
			_output_registers[selected_register] = masked_value;
			evaluate_output_volume();
		});
	}
}

uint8_t AY38910::get_register_value()
{
	// This table ensures that bits that aren't defined within the AY are returned as 1s
	// when read. I can't find documentation on this and don't have a machine to test, so
	// this is provisionally a guess. TODO: investigate.
	const uint8_t register_masks[16] = {
		0x00, 0xf0, 0x00, 0xf0, 0x00, 0xf0, 0xe0, 0x00,
		0xe0, 0xe0, 0xe0, 0x00, 0x00, 0xf0, 0x00, 0x00
	};

	return _registers[_selected_register] | register_masks[_selected_register];
}

uint8_t AY38910::get_port_output(bool port_b)
{
	return _registers[port_b ? 15 : 14];
}

void AY38910::set_data_input(uint8_t r)
{
	_data_input = r;
}

uint8_t AY38910::get_data_output()
{
	return _data_output;
}

void AY38910::set_control_lines(ControlLines control_lines)
{
	ControlState new_state;
	switch((int)control_lines)
	{
		default:					new_state = Inactive;		break;

		case (int)(BCDIR | BC2 | BC1):
		case BCDIR:
		case BC1:					new_state = LatchAddress;	break;

		case (int)(BC2 | BC1):		new_state = Read;			break;
		case (int)(BCDIR | BC2):	new_state = Write;			break;
	}

	if(new_state != _control_state)
	{
		_control_state = new_state;
		switch(new_state)
		{
			default: break;
			case LatchAddress:	select_register(_data_input);			break;
			case Write:			set_register_value(_data_input);		break;
			case Read:			_data_output = get_register_value();	break;
		}
	}
}