From 49ff39abee9fa38601d7d77117edd0e9048c091e Mon Sep 17 00:00:00 2001
From: Laurens Holst <laurens@grauw.nl>
Date: Tue, 3 May 2022 19:32:17 +0200
Subject: [PATCH] AY8930: Fix tone and noise period in expanded mode.

By doubling the internal clock frequency.

In expanded mode, the same tone period is an octave higher than in compat mode.
In expanded mode, the noise period is twice as fast as currently implemented.

See https://github.com/tildearrow/furnace/pull/416
---
 src/engine/platform/ay8930.cpp       | 4 ++--
 src/engine/platform/sound/ay8910.cpp | 8 ++++----
 2 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/src/engine/platform/ay8930.cpp b/src/engine/platform/ay8930.cpp
index 5b823606..3fec732b 100644
--- a/src/engine/platform/ay8930.cpp
+++ b/src/engine/platform/ay8930.cpp
@@ -27,7 +27,7 @@
 #define rWrite(a,v) if (!skipRegisterWrites) {pendingWrites[a]=v;}
 #define immWrite2(a,v) if (!skipRegisterWrites) {writes.emplace(a,v); if (dumpWrites) {addWrite(a,v);} }
 
-#define CHIP_DIVIDER 8
+#define CHIP_DIVIDER 4
 
 const char* regCheatSheetAY8930[]={
   "FreqL_A", "00",
@@ -645,7 +645,7 @@ void DivPlatformAY8930::setFlags(unsigned int flags) {
       chipClock=COLOR_NTSC/2.0;
       break;
   }
-  rate=chipClock/8;
+  rate=chipClock/4;
   for (int i=0; i<3; i++) {
     oscBuf[i]->rate=rate;
   }
diff --git a/src/engine/platform/sound/ay8910.cpp b/src/engine/platform/sound/ay8910.cpp
index 8bb38788..4d19e7de 100644
--- a/src/engine/platform/sound/ay8910.cpp
+++ b/src/engine/platform/sound/ay8910.cpp
@@ -1064,7 +1064,7 @@ void ay8910_device::sound_stream_update(short** outputs, int outLen)
 		{
 			tone = &m_tone[chan];
 			const int period = std::max<int>(1,tone->period);
-			tone->count += is_expanded_mode() ? 16 : 1;
+			tone->count += is_expanded_mode() ? 16 : (m_feature & PSG_HAS_EXPANDED_MODE) ? 2 : 1;
 			while (tone->count >= period)
 			{
 				tone->duty_cycle = (tone->duty_cycle - 1) & 0x1f;
@@ -1080,7 +1080,7 @@ void ay8910_device::sound_stream_update(short** outputs, int outLen)
 			 * channels.
 			 */
 			m_count_noise = 0;
-			m_prescale_noise ^= 1;
+			m_prescale_noise = (m_prescale_noise + 1) & ((m_feature & PSG_HAS_EXPANDED_MODE) ? 3 : 1);
 
 			if (!m_prescale_noise || is_expanded_mode()) // AY8930 noise generator rate is twice compares as compatibility mode
 			{
@@ -1469,7 +1469,7 @@ ay8910_device::ay8910_device(device_type type, unsigned int clock,
     m_noise_latch(0),
 		m_mode(0),
 		m_env_step_mask((!(feature & PSG_HAS_EXPANDED_MODE)) && (psg_type == PSG_TYPE_AY) ? 0x0f : 0x1f),
-		m_step(         (!(feature & PSG_HAS_EXPANDED_MODE)) && (psg_type == PSG_TYPE_AY) ? 2 : 1),
+		m_step(         (feature & PSG_HAS_EXPANDED_MODE) || (psg_type == PSG_TYPE_AY) ? 2 : 1),
 		m_zero_is_off(  (!(feature & PSG_HAS_EXPANDED_MODE)) && (psg_type == PSG_TYPE_AY) ? 1 : 0),
 		m_par(          (!(feature & PSG_HAS_EXPANDED_MODE)) && (psg_type == PSG_TYPE_AY) ? &ay8910_param : &ym2149_param),
 		m_par_env(      (!(feature & PSG_HAS_EXPANDED_MODE)) && (psg_type == PSG_TYPE_AY) ? &ay8910_param : &ym2149_param_env),
@@ -1502,7 +1502,7 @@ void ay8910_device::set_type(psg_type_t psg_type)
 	else
 	{
 		m_env_step_mask = 0x1f;
-		m_step = 1;
+		m_step = (m_feature & PSG_HAS_EXPANDED_MODE) ? 2 : 1;
 		m_zero_is_off = 0;
 		m_par = &ym2149_param;
 		m_par_env = &ym2149_param_env;