ymfm: Latch the multi-frequency state at key on. Fixes sor2 punch sou…

…nd on megadriv.
mamedev · Apr 5, 2021 · 90d6b1b · 90d6b1b
1 parent 4e33773
commit 90d6b1b
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Showing 2 changed files with 19 additions and 5 deletions.
diff --git a/src/devices/sound/ymfm.cpp b/src/devices/sound/ymfm.cpp
@@ -1054,7 +1054,8 @@ void ymopm_registers::log_keyon(u32 choffs, u32 opoffs)
 template<bool IsOpnA>
 ymopn_registers_base<IsOpnA>::ymopn_registers_base() :
 	m_lfo_counter(0),
-	m_lfo_am(0)
+	m_lfo_am(0),
+	m_multi_freq(0)
 {
 	// create the waveforms
 	for (int index = 0; index < WAVEFORM_LENGTH; index++)
@@ -1073,6 +1074,7 @@ void ymopn_registers_base<IsOpnA>::save(device_t &device)
 	{
 		device.save_item(YMFM_NAME(m_lfo_counter));
 		device.save_item(YMFM_NAME(m_lfo_am));
+		device.save_item(YMFM_NAME(m_multi_freq));
 	}
 	device.save_item(YMFM_NAME(m_regdata));
 }
@@ -1177,11 +1179,22 @@ bool ymopn_registers_base<IsOpnA>::write(u16 index, u8 data, u32 &channel, u32 &
 	// handle writes to the key on index
 	if (index == 0x28)
 	{
+		// channel in low 2 bits; channel 3 is not valid
 		channel = BIT(data, 0, 2);
 		if (channel == 3)
 			return false;
+
+		// upper channels for OPNA
 		if (IsOpnA)
 			channel += BIT(data, 2, 1) * 3;
+
+		// when channel 2 key on hits, latch the multifrequency state
+		// megadriv sor2 flips the multi_freq bit on and off during playback
+		// of its sounds, specifically the punch sound
+		if (channel == 2)
+			m_multi_freq = multi_freq();
+
+		// operator mask is the top 4 bits
 		opmask = BIT(data, 4, 4);
 		return true;
 	}
@@ -1276,7 +1289,7 @@ void ymopn_registers_base<IsOpnA>::cache_operator_data(u32 choffs, u32 opoffs, y
 
 	// if multi-frequency mode is enabled and this is channel 2,
 	// fetch one of the special frequencies
-	if (multi_freq() && choffs == 2)
+	if (m_multi_freq && choffs == 2)
 	{
 		if (opoffs == 2)
 			block_freq = cache.block_freq = multi_block_freq(1);
@@ -1388,7 +1401,7 @@ void ymopn_registers_base<IsOpnA>::log_keyon(u32 choffs, u32 opoffs)
 	u32 opnum = (opoffs & 15) - ((opoffs & 15) / 4) + 12 * BIT(opoffs, 8);
 
 	u32 block_freq = ch_block_freq(choffs);
-	if (multi_freq() && choffs == 2)
+	if (m_multi_freq && choffs == 2)
 	{
 		if (opoffs == 2)
 			block_freq = multi_block_freq(1);
@@ -1427,7 +1440,7 @@ void ymopn_registers_base<IsOpnA>::log_keyon(u32 choffs, u32 opoffs)
 		LOG(" pm=%d", ch_lfo_pm_sens(choffs));
 	if (am || pm)
 		LOG(" lfo=%02X", lfo_rate());
-	if (multi_freq() && choffs == 2)
+	if (m_multi_freq && choffs == 2)
 		LOG(" multi=1");
 }
 

diff --git a/src/devices/sound/ymfm.h b/src/devices/sound/ymfm.h
@@ -577,7 +577,7 @@ class ymopn_registers_base : public ymfm_registers_base
 	u32 lfo_rate() const                   { return IsOpnA ? byte(0x22, 0, 3) : 0; }
 	u32 timer_a_value() const              { return word(0x24, 0, 8, 0x25, 0, 2); }
 	u32 timer_b_value() const              { return byte(0x26, 0, 8); }
-	u32 csm() const                        { return (byte(0x27, 6, 2) == 2); }
+	u32 csm() const                        { return byte(0x27, 7, 1); }
 	u32 multi_freq() const                 { return (byte(0x27, 6, 2) != 0); }
 	u32 reset_timer_b() const              { return byte(0x27, 5, 1); }
 	u32 reset_timer_a() const              { return byte(0x27, 4, 1); }
@@ -629,6 +629,7 @@ class ymopn_registers_base : public ymfm_registers_base
 	// internal state
 	u32 m_lfo_counter;               // LFO counter
 	u8 m_lfo_am;                     // current LFO AM value
+	u8 m_multi_freq;                 // channel 2 is currently multi-frequency
 	u8 m_regdata[REGISTERS];         // register data
 	u16 m_waveform[WAVEFORMS][WAVEFORM_LENGTH]; // waveforms
 };