From 1d288b08b6f58f9f11c33c14976002c7bf0b70e3 Mon Sep 17 00:00:00 2001
From: Thomas Harte <thomas.harte@gmail.com>
Date: Thu, 19 Nov 2020 21:19:27 -0500
Subject: [PATCH] Attempts the two most basic forms of DOC output.

Sans interrupts. Or register reads of any variety.
---
 Machines/Apple/AppleIIgs/AppleIIgs.cpp |  2 +-
 Machines/Apple/AppleIIgs/Sound.cpp     | 70 ++++++++++++++++++++++++--
 Machines/Apple/AppleIIgs/Sound.hpp     |  3 ++
 3 files changed, 71 insertions(+), 4 deletions(-)

diff --git a/Machines/Apple/AppleIIgs/AppleIIgs.cpp b/Machines/Apple/AppleIIgs/AppleIIgs.cpp
index ed9f136d7..ef57b4de6 100644
--- a/Machines/Apple/AppleIIgs/AppleIIgs.cpp
+++ b/Machines/Apple/AppleIIgs/AppleIIgs.cpp
@@ -764,7 +764,7 @@ class ConcreteMachine:
 		AudioSource mixer_;
 		Outputs::Speaker::LowpassSpeaker<AudioSource> speaker_;
 		Cycles cycles_since_audio_update_;
-		static constexpr int audio_divider = 8;
+		static constexpr int audio_divider = 16;
 		void update_audio() {
 			const auto divided_cycles = cycles_since_audio_update_.divide(Cycles(audio_divider));
 			sound_glu_.run_for(divided_cycles);
diff --git a/Machines/Apple/AppleIIgs/Sound.cpp b/Machines/Apple/AppleIIgs/Sound.cpp
index 53d6391fe..d7c12fb9c 100644
--- a/Machines/Apple/AppleIIgs/Sound.cpp
+++ b/Machines/Apple/AppleIIgs/Sound.cpp
@@ -74,7 +74,7 @@ void GLU::EnsoniqState::set_register(uint16_t address, uint8_t value) {
 					interrupt_state = value;
 				break;
 				case 0xe1:
-					oscillator_count = (value >> 1) ? (value >> 1) : 1;
+					oscillator_count = 1 + ((value >> 1) & 31);
 				break;
 				case 0xe2:
 					/* Writing to the analogue to digital input definitely makes no sense. */
@@ -164,8 +164,49 @@ void GLU::generate_audio(size_t number_of_samples, std::int16_t *target, int16_t
 	(void)range;
 
 	auto next_store = pending_stores_[pending_store_read_].load(std::memory_order::memory_order_acquire);
-	for(size_t c = 0; c < number_of_samples; c++) {
-		target[c] = 0;
+	for(size_t sample = 0; sample < number_of_samples; sample++) {
+
+		// TODO: there's a bit of a hack here where it is assumed that the input clock has been
+		// divided in advance. Real hardware divides by 8, I think?
+
+		// Seed output as 0.
+		int output = 0;
+
+		// Apply phase updates to all enabled oscillators.
+		for(int c = 0; c < remote_.oscillator_count; c++) {
+			// Don't do anything for halted oscillators.
+			if(remote_.oscillators[c].control&1) continue;
+
+			remote_.oscillators[c].position += remote_.oscillators[c].velocity;
+
+			// Test for a new halting event.
+			switch(remote_.oscillators[c].control & 6) {
+				case 0:	// Free-run mode; just keep the counter to its genuine 24 bits and always update sample.
+					remote_.oscillators[c].position &= 0x00ffffff;
+					output += remote_.oscillators[c].output(remote_.ram_);
+				break;
+
+				case 2:	// One-shot mode; check for end of run. Otherwise update sample.
+					if(remote_.oscillators[c].position & 0xff000000) {
+						remote_.oscillators[c].position = 0;
+						remote_.oscillators[c].control |= 1;
+					} else {
+						output += remote_.oscillators[c].output(remote_.ram_);
+					}
+				break;
+
+				case 4:	// Sync/AM mode.
+					assert(false);
+				break;
+
+				case 6:	// Swap mode.
+					assert(false);
+				break;
+			}
+		}
+
+		// Maximum total output was 32 channels times a 16-bit range. Map that down.
+		target[sample] = (output * output_range_) >> 20;
 
 		// Apply any RAM writes that interleave here.
 		++pending_store_read_time_;
@@ -178,6 +219,29 @@ void GLU::generate_audio(size_t number_of_samples, std::int16_t *target, int16_t
 	}
 }
 
+uint8_t GLU::EnsoniqState::Oscillator::sample(uint8_t *ram) {
+	// Table size mask should be 0x8000 for the largest table size, and 0xff00 for
+	// the smallest.
+	const uint16_t table_size_mask = 0xffff >> (8 - ((table_size >> 3) & 7));
+
+	// The pointer should use (at most) 15 bits; starting with bit 1 for resolution 0
+	// and starting at bit 8 for resolution 7.
+	const uint16_t table_pointer = uint16_t(position >> (1 + table_size&7));
+
+	// The full pointer is composed of the bits of the programmed address not touched by
+	// the table pointer, plus the table pointer.
+	const uint16_t sample_address = (address & ~table_size_mask) | (table_pointer & table_size_mask);
+
+	// Ignored here: bit 6 should select between RAM banks. But for now this is IIgs-centric,
+	// and that has only one bank of RAM.
+	return ram[sample_address];
+}
+
+int16_t GLU::EnsoniqState::Oscillator::output(uint8_t *ram) {
+	// Samples are unsigned 8-bit; do the proper work to make volume work correctly.
+	return int8_t(sample(ram) ^ 128) * volume;
+}
+
 void GLU::skip_audio(EnsoniqState &state, size_t number_of_samples) {
 	(void)number_of_samples;
 	(void)state;
diff --git a/Machines/Apple/AppleIIgs/Sound.hpp b/Machines/Apple/AppleIIgs/Sound.hpp
index c84bd6615..5fb7a3278 100644
--- a/Machines/Apple/AppleIIgs/Sound.hpp
+++ b/Machines/Apple/AppleIIgs/Sound.hpp
@@ -75,6 +75,9 @@ class GLU: public Outputs::Speaker::SampleSource {
 				uint8_t address;
 				uint8_t control;
 				uint8_t table_size;
+
+				uint8_t sample(uint8_t *ram);
+				int16_t output(uint8_t *ram);
 			} oscillators[32];
 
 			// TODO: do all of these need to be on the audio thread?