From 1ff03c81e7a90ba25e254521a250640400be0bdf Mon Sep 17 00:00:00 2001
From: Felipe Correa da Silva Sanches <juca@members.fsf.org>
Date: Sun, 2 Nov 2025 12:37:50 -0300
Subject: [PATCH] [Access Virus] Analog input knobs for Virus A & B

---
 src/devices/cpu/mcs51/sab80c535.cpp |  20 ++
 src/devices/cpu/mcs51/sab80c535.h   |  18 +-
 src/mame/access/acvirus.cpp         | 135 ++++++++++++-
 src/mame/layout/virusb.lay          | 284 +++++++++++++++++++++++++++-
 4 files changed, 452 insertions(+), 5 deletions(-)

diff --git a/src/devices/cpu/mcs51/sab80c535.cpp b/src/devices/cpu/mcs51/sab80c535.cpp
index 2908f418a31b5..c34c3372e5c38 100644
--- a/src/devices/cpu/mcs51/sab80c535.cpp
+++ b/src/devices/cpu/mcs51/sab80c535.cpp
@@ -78,16 +78,34 @@ u8 sab80c535_device::p5_r()
 	return m_p5 & m_port_in_cb[5]();
 }
 
+void sab80c535_device::adcon_w(u8 data)
+{
+	m_adcon = data;
+}
+
+u8 sab80c535_device::adcon_r()
+{
+	return m_adcon;
+}
+
+u8 sab80c535_device::addat_r()
+{
+	return m_an_func[m_adcon & 7]() * 2;
+}
+
 
 void sab80c535_device::sfr_map(address_map &map)
 {
 	i8052_device::sfr_map(map);
+	map(0xd8, 0xd8).rw(FUNC(sab80c535_device::adcon_r), FUNC(sab80c535_device::adcon_w));
+	map(0xd9, 0xd9).r(FUNC(sab80c535_device::addat_r));
 	map(0xe8, 0xe8).rw(FUNC(sab80c535_device::p4_r), FUNC(sab80c535_device::p4_w));
 	map(0xf8, 0xf8).rw(FUNC(sab80c535_device::p5_r), FUNC(sab80c535_device::p5_w));
 }
 
 sab80c535_device::sab80c535_device(const machine_config &mconfig, const char *tag, device_t *owner, u32 clock)
 	: i8052_device(mconfig, SAB80C535, tag, owner, clock, 0)
+	, m_an_func(*this, 0)
 {
 }
 
@@ -96,6 +114,7 @@ void sab80c535_device::device_start()
 	i8052_device::device_start();
 	save_item(NAME(m_p4));
 	save_item(NAME(m_p5));
+	save_item(NAME(m_adcon));
 }
 
 void sab80c535_device::device_reset()
@@ -103,6 +122,7 @@ void sab80c535_device::device_reset()
 	i8052_device::device_reset();
 	m_p4 = 0xff;
 	m_p5 = 0xff;
+	m_adcon = 0x00;
 }
 
 std::unique_ptr<util::disasm_interface> sab80c535_device::create_disassembler()
diff --git a/src/devices/cpu/mcs51/sab80c535.h b/src/devices/cpu/mcs51/sab80c535.h
index 50b077207ece1..5c0b2c1cef540 100644
--- a/src/devices/cpu/mcs51/sab80c535.h
+++ b/src/devices/cpu/mcs51/sab80c535.h
@@ -12,6 +12,15 @@ class sab80c535_device : public i8052_device
 	// construction/destruction
 	sab80c535_device(const machine_config &mconfig, const char *tag, device_t *owner, u32 clock);
 
+	auto an0_func() { return m_an_func[0].bind(); }
+	auto an1_func() { return m_an_func[1].bind(); }
+	auto an2_func() { return m_an_func[2].bind(); }
+	auto an3_func() { return m_an_func[3].bind(); }
+	auto an4_func() { return m_an_func[4].bind(); }
+	auto an5_func() { return m_an_func[5].bind(); }
+	auto an6_func() { return m_an_func[6].bind(); }
+	auto an7_func() { return m_an_func[7].bind(); }
+
 protected:
 	virtual void device_start() override ATTR_COLD;
 	virtual void device_reset() override ATTR_COLD;
@@ -19,13 +28,20 @@ class sab80c535_device : public i8052_device
 	virtual std::unique_ptr<util::disasm_interface> create_disassembler() override;
 	virtual void sfr_map(address_map &map) override ATTR_COLD;
 
+	devcb_read8::array<8> m_an_func;
+
 private:
-	u8 m_p4, m_p5;
+	u8 m_p4;
+	u8 m_p5;
+	u8 m_adcon;
 
 	void p4_w(u8 data);
 	u8 p4_r();
 	void p5_w(u8 data);
 	u8 p5_r();
+	void adcon_w(u8 data);
+	u8 adcon_r();
+	u8 addat_r();
 };
 
 DECLARE_DEVICE_TYPE(SAB80C535, sab80c535_device)
diff --git a/src/mame/access/acvirus.cpp b/src/mame/access/acvirus.cpp
index a53a22cbe8649..ae4339f71b58c 100644
--- a/src/mame/access/acvirus.cpp
+++ b/src/mame/access/acvirus.cpp
@@ -90,7 +90,9 @@ class acvirus_state : public driver_device
 		m_dsp(*this, "dsp"),
 		m_rombank(*this, "rombank"),
 		m_row(*this, "ROW%u", 0U),
-		m_scan(0)
+		m_knob(*this, "knob_%u", 0U),
+		m_scan(0),
+		m_an_select(0)
 	{ }
 
 	void virusa(machine_config &config) ATTR_COLD;
@@ -119,13 +121,17 @@ class acvirus_state : public driver_device
 	u8 p1_r();
 	u8 p4_r();
 	void p1_w(u8 data);
+	void p3_w(u8 data);
 	void p5_w(u8 data);
 
 	u8 p402_r();
 
 	void palette_init(palette_device &palette) ATTR_COLD;
 
+	required_ioport_array<32> m_knob;
+
 	u8 m_scan;
+	u8 m_an_select;
 };
 
 
@@ -135,6 +141,7 @@ void acvirus_state::machine_start()
 	m_rombank->set_entry(3);
 
 	save_item(NAME(m_scan));
+	save_item(NAME(m_an_select));
 }
 
 void acvirus_state::machine_reset()
@@ -154,6 +161,11 @@ void acvirus_state::p1_w(u8 data)
 	m_lcdc->rs_w(BIT(data, 7));
 }
 
+void acvirus_state::p3_w(u8 data)
+{
+	m_an_select = (data >> 4) & 3;
+}
+
 u8 acvirus_state::p4_r()
 {
 	return m_row[m_scan & 3]->read();
@@ -205,8 +217,17 @@ void acvirus_state::virusa(machine_config &config)
 	m_maincpu->set_addrmap(AS_DATA,    &acvirus_state::data_map);
 	m_maincpu->port_in_cb<1>().set(FUNC(acvirus_state::p1_r));
 	m_maincpu->port_out_cb<1>().set(FUNC(acvirus_state::p1_w));
+	m_maincpu->port_out_cb<3>().set(FUNC(acvirus_state::p3_w));
 	m_maincpu->port_in_cb<4>().set(FUNC(acvirus_state::p4_r));
 	m_maincpu->port_out_cb<5>().set(FUNC(acvirus_state::p5_w));
+	m_maincpu->an0_func().set([this] { return m_knob[4*0 + m_an_select]->read(); });
+	m_maincpu->an1_func().set([this] { return m_knob[4*1 + m_an_select]->read(); });
+	m_maincpu->an2_func().set([this] { return m_knob[4*2 + m_an_select]->read(); });
+	m_maincpu->an3_func().set([this] { return m_knob[4*3 + m_an_select]->read(); });
+	m_maincpu->an4_func().set([this] { return m_knob[4*4 + m_an_select]->read(); });
+	m_maincpu->an5_func().set([this] { return m_knob[4*5 + m_an_select]->read(); });
+	m_maincpu->an6_func().set([this] { return m_knob[4*6 + m_an_select]->read(); });
+	m_maincpu->an7_func().set([this] { return m_knob[4*7 + m_an_select]->read(); });
 
 	screen_device &screen(SCREEN(config, "screen", SCREEN_TYPE_LCD));
 	screen.set_refresh_hz(60);
@@ -237,8 +258,17 @@ void acvirus_state::virusb(machine_config &config)
 	m_maincpu->set_addrmap(AS_DATA,    &acvirus_state::data_map);
 	m_maincpu->port_in_cb<1>().set(FUNC(acvirus_state::p1_r));
 	m_maincpu->port_out_cb<1>().set(FUNC(acvirus_state::p1_w));
+	m_maincpu->port_out_cb<3>().set(FUNC(acvirus_state::p3_w));
 	m_maincpu->port_in_cb<4>().set(FUNC(acvirus_state::p4_r));
 	m_maincpu->port_out_cb<5>().set(FUNC(acvirus_state::p5_w));
+	m_maincpu->an0_func().set([this] { return m_knob[4*0 + m_an_select]->read(); });
+	m_maincpu->an1_func().set([this] { return m_knob[4*1 + m_an_select]->read(); });
+	m_maincpu->an2_func().set([this] { return m_knob[4*2 + m_an_select]->read(); });
+	m_maincpu->an3_func().set([this] { return m_knob[4*3 + m_an_select]->read(); });
+	m_maincpu->an4_func().set([this] { return m_knob[4*4 + m_an_select]->read(); });
+	m_maincpu->an5_func().set([this] { return m_knob[4*5 + m_an_select]->read(); });
+	m_maincpu->an6_func().set([this] { return m_knob[4*6 + m_an_select]->read(); });
+	m_maincpu->an7_func().set([this] { return m_knob[4*7 + m_an_select]->read(); });
 
 	screen_device &screen(SCREEN(config, "screen", SCREEN_TYPE_LCD));
 	screen.set_refresh_hz(60);
@@ -297,7 +327,108 @@ void acvirus_state::virusc(machine_config &config)
 }
 
 
+INPUT_PORTS_START( virusa_knobs )
+	PORT_START("knob_0")
+	PORT_ADJUSTER(64, "Master Volume") PORT_MINMAX(0, 127)
+
+	PORT_START("knob_1")
+	PORT_ADJUSTER(64, "Definable 1") PORT_MINMAX(0, 127)
+
+	PORT_START("knob_2")
+	PORT_ADJUSTER(64, "Definable 2") PORT_MINMAX(0, 127)
+
+	PORT_START("knob_3")
+	PORT_ADJUSTER(64, "LFO 1: Rate") PORT_MINMAX(0, 127)
+
+	PORT_START("knob_4")
+	PORT_ADJUSTER(64, "LFO 2: Rate") PORT_MINMAX(0, 127)
+
+	PORT_START("knob_5")
+	PORT_ADJUSTER(64, "Osc 1: Shape") PORT_MINMAX(0, 127)
+
+	PORT_START("knob_6")
+	PORT_ADJUSTER(64, "Osc 1: Wave/PW") PORT_MINMAX(0, 127)
+
+	PORT_START("knob_7")
+	PORT_ADJUSTER(64, "Osc 2: Shape") PORT_MINMAX(0, 127)
+
+	PORT_START("knob_8")
+	PORT_ADJUSTER(64, "Osc 2: Wave/PW") PORT_MINMAX(0, 127)
+
+	PORT_START("knob_9")
+	PORT_ADJUSTER(64, "Osc 2 Semitone") PORT_MINMAX(0, 127)
+
+	PORT_START("knob_10")
+	PORT_ADJUSTER(64, "Osc 2 Detune") PORT_MINMAX(0, 127)
+
+	PORT_START("knob_11")
+	PORT_ADJUSTER(64, "Osc 2 FM Amount") PORT_MINMAX(0, 127)
+
+	PORT_START("knob_12")
+	PORT_ADJUSTER(64, "Mixer Osc Bal") PORT_MINMAX(0, 127)
+
+	PORT_START("knob_13")
+	PORT_ADJUSTER(64, "Mixer Sub Osc") PORT_MINMAX(0, 127)
+
+	PORT_START("knob_14")
+	PORT_ADJUSTER(64, "Mixer Osc Volume") PORT_MINMAX(0, 127)
+
+	PORT_START("knob_15")
+	PORT_ADJUSTER(64, "Value (Program)") PORT_MINMAX(0, 127)
+
+	PORT_START("knob_16")
+	PORT_ADJUSTER(64, "Cutoff") PORT_MINMAX(0, 127)
+
+	PORT_START("knob_17")
+	PORT_ADJUSTER(64, "Cutoff 2") PORT_MINMAX(0, 127)
+
+	PORT_START("knob_18")
+	PORT_ADJUSTER(64, "Filter Attack") PORT_MINMAX(0, 127)
+
+	PORT_START("knob_19")
+	PORT_ADJUSTER(64, "Amp Attack") PORT_MINMAX(0, 127)
+
+	PORT_START("knob_20")
+	PORT_ADJUSTER(64, "Filter Resonance") PORT_MINMAX(0, 127)
+
+	PORT_START("knob_21")
+	PORT_ADJUSTER(64, "Filter EnvAmount") PORT_MINMAX(0, 127)
+
+	PORT_START("knob_22")
+	PORT_ADJUSTER(64, "Filter Key Follow") PORT_MINMAX(0, 127)
+
+	PORT_START("knob_23")
+	PORT_ADJUSTER(64, "Filter Balance") PORT_MINMAX(0, 127)
+
+	PORT_START("knob_24")
+	PORT_ADJUSTER(64, "Filter Decay") PORT_MINMAX(0, 127)
+
+	PORT_START("knob_25")
+	PORT_ADJUSTER(64, "Filter Sustain") PORT_MINMAX(0, 127)
+
+	PORT_START("knob_26")
+	PORT_ADJUSTER(64, "Filter Time") PORT_MINMAX(0, 127)
+
+	PORT_START("knob_27")
+	PORT_ADJUSTER(64, "Filter Release") PORT_MINMAX(0, 127)
+
+	PORT_START("knob_28")
+	PORT_ADJUSTER(64, "Amp Decay") PORT_MINMAX(0, 127)
+
+	PORT_START("knob_29")
+	PORT_ADJUSTER(64, "Amp Sustain") PORT_MINMAX(0, 127)
+
+	PORT_START("knob_30")
+	PORT_ADJUSTER(64, "Amp Time") PORT_MINMAX(0, 127)
+
+	PORT_START("knob_31")
+	PORT_ADJUSTER(64, "Amp Release") PORT_MINMAX(0, 127)
+INPUT_PORTS_END
+
+
 static INPUT_PORTS_START( virusa )
+	PORT_INCLUDE( virusa_knobs )
+
 	PORT_START("ROW0")
 	PORT_BIT(0x01, IP_ACTIVE_LOW, IPT_OTHER) PORT_CODE(KEYCODE_1) PORT_NAME("Key Follow")
 	PORT_BIT(0x02, IP_ACTIVE_LOW, IPT_OTHER) PORT_CODE(KEYCODE_V) PORT_NAME("Multi")
@@ -340,6 +471,8 @@ INPUT_PORTS_END
 
 
 static INPUT_PORTS_START( virusb )
+	PORT_INCLUDE( virusa_knobs )
+
 	PORT_START("ROW0")
 	PORT_BIT(0x01, IP_ACTIVE_LOW, IPT_OTHER) PORT_CODE(KEYCODE_1) PORT_NAME("LFO 1: Edit")
 	PORT_BIT(0x02, IP_ACTIVE_LOW, IPT_OTHER) PORT_CODE(KEYCODE_V) PORT_NAME("Multi")
diff --git a/src/mame/layout/virusb.lay b/src/mame/layout/virusb.lay
index 1facfac9e88e3..c408792f1ff27 100644
--- a/src/mame/layout/virusb.lay
+++ b/src/mame/layout/virusb.lay
@@ -60,7 +60,22 @@ license:CC0-1.0
 		<disk><color red="0.8" green="0.8" blue="0.8"/><bounds x="0" y="0" width="5" height="5"/></disk>
 	</element>
 
-	<element name="knob">
+
+	<element name="transparent"><rect><color red="0.0" green="0.0" blue="0.0" alpha="0.0"/></rect></element>
+	<element name="knob_outer"><disk><color red="0.0" green="0.0" blue="0.0" alpha="0.0"/></disk></element>
+	<element name="knob_value">
+		<simplecounter maxstate="100" digits="1"><color red="0.8" green="0.8" blue="0.8"/></simplecounter>
+	</element>
+	<group name="knob">
+		<element ref="knob_outer" id="knob_~knob_input~"><bounds x="0" y="0" width="68" height="68"/></element>
+		<element ref="knob_value" inputtag="~knob_input~" inputmask="0xffff" inputraw="yes">
+			<bounds x="17" y="27" width="34" height="24"/>
+		</element>
+		<element ref="transparent" clickthrough="no"><bounds x="17" y="22" width="34" height="24"/></element>
+	</group>
+
+
+	<element name="rotating_knob">
 		<disk>
 			<color red="0" green="0" blue="0"/>
 			<bounds x="0" y="0" width="47" height="47"/>
@@ -69,10 +84,14 @@ license:CC0-1.0
 			<color red="0.13" green="0.13" blue="0.13"/>
 			<bounds x="2" y="2" width="43" height="43"/>
 		</disk>
+		<!-- For now ommit the tick. I'd like to animate it later using
+		     currently unsupported element rotations with arbitrary angles:
+
 		<rect>
 			<color red="0.6" green="0.6" blue="0.6"/>
 			<bounds x="22" y="2" width="3" height="12"/>
 		</rect>
+		-->
 		<disk>
 			<color red="1" green="1" blue="1" alpha="0.05"/>
 			<bounds x="5" y="5" width="37" height="37"/>
@@ -81,7 +100,7 @@ license:CC0-1.0
 
 	<group name="knob_base">
 		<!-- body -->
-		<element ref="knob">
+		<element ref="rotating_knob">
 			<bounds x="15" y="12" width="47" height="47"/>
 		</element>
 
@@ -562,10 +581,18 @@ license:CC0-1.0
 <!-- FIXME: All input tags and input masks here are incorrect. They're just place holders for now -->
 
 		<group ref="knob_0_6_12"><!-- MASTER VOLUME --><bounds x="99" y="115" width="77" height="77"/></group>
+		<param name="knob_input" value="knob_0"/>
+		<group ref="knob"><bounds x="99" y="115" width="77" height="77"/></group>
 		<element ref="master_volume_text"><bounds x="90" y="196" width="96" height="12"/></element>
+
 		<group ref="knob_0_6_12"><!-- DEFINABLE 1 --><bounds x="99" y="223" width="77" height="77"/></group>
+		<param name="knob_input" value="knob_1"/>
+		<group ref="knob"><bounds x="99" y="223" width="77" height="77"/></group>
 		<element ref="definable_1_text"><bounds x="99" y="304" width="81" height="12"/></element>
+
 		<group ref="knob_0_6_12"><!-- DEFINABLE 2 --><bounds x="99" y="330" width="77" height="77"/></group>
+		<param name="knob_input" value="knob_2"/>
+		<group ref="knob"><bounds x="99" y="330" width="77" height="77"/></group>
 		<element ref="definable_2_text"><bounds x="99" y="411" width="81" height="12"/></element>
 
 		<element ref="minus2_text"><bounds x="98" y="462" width="12" height="12"/></element>
@@ -590,6 +617,8 @@ license:CC0-1.0
 		<element ref="lfo_1_text"><bounds x="209" y="84" width="47" height="16"/></element>
 
 		<group ref="knob_0_6_12"><!-- RATE --><bounds x="209" y="115" width="77" height="77"/></group>
+		<param name="knob_input" value="knob_3"/>
+		<group ref="knob"><bounds x="209" y="115" width="77" height="77"/></group>
 		<element ref="rate_text"><bounds x="235" y="196" width="28" height="12"/></element>
 
 		<element ref="led" name="LED5"><bounds x="292" y="108" width="11" height="11"/></element>
@@ -637,6 +666,8 @@ license:CC0-1.0
 <!-- LFO 2 -->
 		<element ref="lfo_2_text"><bounds x="209" y="335" width="48" height="16"/></element>
 		<group ref="knob_0_6_12"><!-- RATE --><bounds x="209" y="360" width="77" height="77"/></group>
+		<param name="knob_input" value="knob_4"/>
+		<group ref="knob"><bounds x="209" y="360" width="77" height="77"/></group>
 		<element ref="rate_text"><bounds x="235" y="440" width="28" height="12"/></element>
 
 		<element ref="led" name="LED18"><bounds x="292" y="353" width="11" height="11"/></element>
@@ -687,9 +718,13 @@ license:CC0-1.0
 		<element ref="1_text"><bounds x="500" y="102" width="8" height="16"/></element>
 
 		<group ref="knob_wave"><!-- SHAPE --><bounds x="495" y="115" width="88" height="74"/></group>
+		<param name="knob_input" value="knob_5"/>
+		<group ref="knob"><bounds x="498" y="115" width="88" height="74"/></group>
 		<element ref="shape_text"><bounds x="525" y="196" width="36" height="12"/></element>
 
 		<group ref="knob_0_6_12"><!-- WAVE SEL / PW --><bounds x="504" y="223" width="77" height="77"/></group>
+		<param name="knob_input" value="knob_6"/>
+		<group ref="knob"><bounds x="504" y="223" width="77" height="77"/></group>
 		<group ref="wave_sel_pill_text"><bounds x="504" y="301" width="50" height="13"/></group>
 		<element ref="slash_pw_text"><bounds x="557" y="302" width="22" height="12"/></element>
 
@@ -697,15 +732,23 @@ license:CC0-1.0
 		<element ref="2_text"><bounds x="613" y="102" width="9" height="16"/></element>
 
 		<group ref="knob_wave"><!-- SHAPE --><bounds x="602" y="115" width="88" height="74"/></group>
+		<param name="knob_input" value="knob_7"/>
+		<group ref="knob"><bounds x="605" y="115" width="88" height="74"/></group>
 		<element ref="shape_text"><bounds x="633" y="196" width="36" height="12"/></element>
 
 		<group ref="knob_48"><!-- SEMITONE --><bounds x="720" y="115" width="77" height="77"/></group>
+		<param name="knob_input" value="knob_10"/>
+		<group ref="knob"><bounds x="720" y="115" width="77" height="77"/></group>
 		<element ref="semitone_text"><bounds x="730" y="196" width="59" height="12"/></element>
 
 		<group ref="knob_0_6_12"><!-- DETUNE --><bounds x="830" y="115" width="77" height="77"/></group>
+		<param name="knob_input" value="knob_9"/>
+		<group ref="knob"><bounds x="830" y="115" width="77" height="77"/></group>
 		<element ref="detune_text"><bounds x="845" y="196" width="44" height="12"/></element>
 
 		<group ref="knob_0_6_12"><!-- WAVE SEL / PW --><bounds x="613" y="223" width="77" height="77"/></group>
+		<param name="knob_input" value="knob_8"/>
+		<group ref="knob"><bounds x="613" y="223" width="77" height="77"/></group>
 		<group ref="wave_sel_pill_text"><bounds x="613" y="301" width="50" height="13"/></group>
 		<element ref="slash_pw_text"><bounds x="666" y="302" width="22" height="12"/></element>
 
@@ -719,16 +762,26 @@ license:CC0-1.0
 		<element ref="sync_text"><bounds x="769" y="300" width="29" height="12"/></element>
 
 		<group ref="knob_0_6_12"><!-- FM AMOUNT --><bounds x="830" y="223" width="77" height="77"/></group>
+		<param name="knob_input" value="knob_11"/>
+		<group ref="knob"><bounds x="830" y="223" width="77" height="77"/></group>
 		<element ref="fm_amount_text"><bounds x="834" y="300" width="66" height="12"/></element>
 
 <!-- MIX -->
 		<element ref="mix_text"><bounds x="935" y="84" width="29" height="16"/></element>
 
 		<group ref="knob_1plus2"><!-- OSC BAL --><bounds x="935" y="115" width="77" height="77"/></group>
+		<param name="knob_input" value="knob_12"/>
+		<group ref="knob"><bounds x="935" y="115" width="77" height="77"/></group>
 		<element ref="osc_bal_text"><bounds x="947" y="196" width="52" height="12"/></element>
+
 		<group ref="knob_0_6_12"><!-- SUB OSC --><bounds x="935" y="223" width="77" height="77"/></group>
+		<param name="knob_input" value="knob_13"/>
+		<group ref="knob"><bounds x="935" y="223" width="77" height="77"/></group>
 		<element ref="sub_osc_text"><bounds x="948" y="300" width="51" height="12"/></element>
+
 		<group ref="knob_saturation"><!-- OSC VOL --><bounds x="935" y="330" width="77" height="77"/></group>
+		<param name="knob_input" value="knob_14"/>
+		<group ref="knob"><bounds x="935" y="330" width="77" height="77"/></group>
 		<element ref="osc_vol_text"><bounds x="947" y="405" width="52" height="12"/></element>
 
 		<!-- The display -->
@@ -801,7 +854,9 @@ license:CC0-1.0
 		<element ref="plus_text"><bounds x="890" y="547" width="6" height="12"/></element>
 		<element ref="program_text"><bounds x="836" y="558" width="34" height="9"/></element>
 
-		<group ref="knob_0_6_12"><!-- PROGRAM --><bounds x="935" y="463" width="77" height="77"/></group>
+		<group ref="knob_0_6_12"><!-- Value (Program) --><bounds x="935" y="463" width="77" height="77"/></group>
+		<param name="knob_input" value="knob_15"/>
+		<group ref="knob"><bounds x="935" y="463" width="77" height="77"/></group>
 		<element ref="value_program_connector"><bounds x="876" y="538" width="98" height="27"/></element>
 
 
@@ -809,25 +864,37 @@ license:CC0-1.0
 		<element ref="filters_text"><bounds x="1102" y="84" width="68" height="16"/></element>
 
 		<group ref="knob_0_6_12"><!-- CUTOFF --><bounds x="1075" y="115" width="77" height="77"/></group>
+		<param name="knob_input" value="knob_16"/>
+		<group ref="knob"><bounds x="1075" y="115" width="77" height="77"/></group>
 		<element ref="cutoff_text"><bounds x="1093" y="196" width="40" height="12"/></element>
 
 		<group ref="knob_0_6_12"><!-- RESONANCE --><bounds x="1185" y="115" width="77" height="77"/></group>
+		<param name="knob_input" value="knob_20"/>
+		<group ref="knob"><bounds x="1185" y="115" width="77" height="77"/></group>
 		<element ref="resonance_text"><bounds x="1190" y="196" width="66" height="12"/></element>
 
 		<group ref="knob_0_6_12"><!-- ENV AMOUNT --><bounds x="1295" y="115" width="77" height="77"/></group>
+		<param name="knob_input" value="knob_21"/>
+		<group ref="knob"><bounds x="1295" y="115" width="77" height="77"/></group>
 		<element ref="env_amount_text"><bounds x="1299" y="196" width="70" height="12"/></element>
 
 		<group ref="knob_100pc"><!-- KEYFOLLOW --><bounds x="1405" y="115" width="77" height="77"/></group>
+		<param name="knob_input" value="knob_22"/>
+		<group ref="knob"><bounds x="1405" y="115" width="77" height="77"/></group>
 		<element ref="keyfollow_text"><bounds x="1412" y="196" width="63" height="12"/></element>
 
 		<element ref="filter_connector"><bounds x="1184" y="192" width="370" height="28"/></element>
 
 		<group ref="knob_1plus2"><!-- FILTER BALANCE --><bounds x="1515" y="115" width="77" height="77"/></group>
+		<param name="knob_input" value="knob_23"/>
+		<group ref="knob"><bounds x="1515" y="115" width="77" height="77"/></group>
 		<element ref="filter_balance_text"><bounds x="1511" y="196" width="84" height="12"/></element>
 		<element ref="filt_1_text"><bounds x="1512" y="212" width="27" height="12"/></element>
 		<element ref="filt_2_text"><bounds x="1558" y="212" width="28" height="12"/></element>
 
 		<group ref="knob_6"><!-- CUTOFF 2 --><bounds x="1075" y="223" width="77" height="77"/></group>
+		<param name="knob_input" value="knob_17"/>
+		<group ref="knob"><bounds x="1075" y="223" width="77" height="77"/></group>
 		<element ref="cutoff_2_text"><bounds x="1084" y="300" width="59" height="12"/></element>
 
 		<element ref="led" name="LED38"><bounds x="1197" y="230" width="11" height="11"/></element>
@@ -885,20 +952,30 @@ license:CC0-1.0
 		<element ref="select_text"><bounds x="1526" y="300" width="44" height="12"/></element>
 
 		<group ref="knob_0_6_12"><!-- ATTACK --><bounds x="1075" y="330" width="77" height="77"/></group>
+		<param name="knob_input" value="knob_18"/>
+		<group ref="knob"><bounds x="1075" y="330" width="77" height="77"/></group>
 		<element ref="attack_text"><bounds x="1091" y="405" width="44" height="12"/></element>
 
 		<group ref="knob_0_6_12"><!-- DECAY --><bounds x="1185" y="330" width="77" height="77"/></group>
+		<param name="knob_input" value="knob_24"/>
+		<group ref="knob"><bounds x="1185" y="330" width="77" height="77"/></group>
 		<element ref="decay_text"><bounds x="1207" y="405" width="37" height="12"/></element>
 
 		<group ref="knob_0_6_12"><!-- SUSTAIN --><bounds x="1295" y="330" width="77" height="77"/></group>
+		<param name="knob_input" value="knob_25"/>
+		<group ref="knob"><bounds x="1295" y="330" width="77" height="77"/></group>
 		<element ref="sustain_text"><bounds x="1308" y="405" width="51" height="12"/></element>
 
 		<element ref="gray_line"><bounds x="1360" y="413" width="71" height="1"/></element>
 
 		<group ref="knob_fall_rise"><!-- TIME --><bounds x="1405" y="326" width="77" height="81"/></group>
+		<param name="knob_input" value="knob_26"/>
+		<group ref="knob"><bounds x="1405" y="326" width="77" height="81"/></group>
 		<element ref="time_text"><bounds x="1431" y="405" width="29" height="12"/></element>
 
 		<group ref="knob_0_6_12"><!-- RELEASE --><bounds x="1515" y="330" width="77" height="77"/></group>
+		<param name="knob_input" value="knob_27"/>
+		<group ref="knob"><bounds x="1515" y="330" width="77" height="77"/></group>
 		<element ref="release_text"><bounds x="1526" y="405" width="51" height="12"/></element>
 
 
@@ -906,21 +983,222 @@ license:CC0-1.0
 		<element ref="amplifier_text"><bounds x="1086" y="437" width="99" height="16"/></element>
 
 		<group ref="knob_0_6_12"><!-- ATTACK --><bounds x="1075" y="463" width="77" height="77"/></group>
+		<param name="knob_input" value="knob_19"/>
+		<group ref="knob"><bounds x="1075" y="463" width="77" height="77"/></group>
 		<element ref="attack_text"><bounds x="1091" y="543" width="44" height="12"/></element>
 
 		<group ref="knob_0_6_12"><!-- DECAY --><bounds x="1185" y="463" width="77" height="77"/></group>
+		<param name="knob_input" value="knob_28"/>
+		<group ref="knob"><bounds x="1185" y="463" width="77" height="77"/></group>
 		<element ref="decay_text"><bounds x="1207" y="543" width="37" height="12"/></element>
 
 		<group ref="knob_0_6_12"><!-- SUSTAIN --><bounds x="1295" y="463" width="77" height="77"/></group>
+		<param name="knob_input" value="knob_29"/>
+		<group ref="knob"><bounds x="1295" y="463" width="77" height="77"/></group>
 		<element ref="sustain_text"><bounds x="1308" y="543" width="51" height="12"/></element>
 
 		<element ref="gray_line"><bounds x="1360" y="551" width="71" height="1"/></element>
 
 		<group ref="knob_fall_rise"><!-- TIME --><bounds x="1405" y="459" width="77" height="81"/></group>
+		<param name="knob_input" value="knob_30"/>
+		<group ref="knob"><bounds x="1405" y="459" width="77" height="81"/></group>
 		<element ref="time_text"><bounds x="1431" y="543" width="29" height="12"/></element>
 
 		<group ref="knob_0_6_12"><!-- RELEASE --><bounds x="1515" y="463" width="77" height="77"/></group>
+		<param name="knob_input" value="knob_31"/>
+		<group ref="knob"><bounds x="1515" y="463" width="77" height="77"/></group>
 		<element ref="release_text"><bounds x="1526" y="543" width="51" height="12"/></element>
 	</view>
 
+	<script><![CDATA[
+		file:set_resolve_tags_callback(
+			function()
+				local view = file.views["Default Layout"]
+				install_slider_callbacks(view)
+
+				for i = 0, 31 do
+					local knob_input = "knob_" .. i
+					add_knob(view, "knob_" .. knob_input, knob_input, 3.5, HORIZONTAL)
+				end
+			end)
+
+		-----------------------------------------------------------------------
+		-- Slider and knob library starts.
+		-- Can be copied as-is to other layouts.
+		-----------------------------------------------------------------------
+		VERTICAL = 0
+		HORIZONTAL = 1
+
+		local widgets = {}   -- Stores slider and knob information.
+		local pointers = {}  -- Tracks pointer state.
+
+		-- The knob's Y position must be animated using <animate inputtag="{port_name}">.
+		-- The click area's vertical size must exactly span the range of the
+		-- knob's movement.
+		function add_slider(view, clickarea_id, knob_id, port_name)
+			table.insert(widgets, {
+				clickarea   = get_layout_item(view, clickarea_id),
+				slider_knob = get_layout_item(view, knob_id),
+				field       = get_port_field(port_name),
+				is_knob     = false })
+		end
+
+		-- A sweep between the attached field's min and max values requires
+		-- moving the pointer by `scale * clickarea.height` pixes.
+		function add_knob(view, clickarea_id, port_name, scale, drag_direction)
+			table.insert(widgets, {
+				clickarea     = get_layout_item(view, clickarea_id),
+				field         = get_port_field(port_name),
+				is_knob       = true,
+				scale         = scale,
+				is_horizontal = (drag_direction == HORIZONTAL) })
+		end
+
+		function get_layout_item(view, item_id)
+			local item = view.items[item_id]
+			if item == nil then
+				emu.print_error("Layout element: '" .. item_id .. "' not found.")
+			end
+			return item
+		end
+
+		function get_port_field(port_name)
+			local port = file.device:ioport(port_name)
+			if port == nil then
+				emu.print_error("Port: '" .. port_name .. "' not found.")
+				return nil
+			end
+			local field = nil
+			for k, val in pairs(port.fields) do
+				field = val
+				break
+			end
+			local field_msg = "Needs to either be an IPT_ADJUSTER, or an analog port with auto-center."
+			if field == nil then
+				emu.print_error("Port '" .. port_name .."' " .. field_msg)
+				return nil
+			end
+			if field.is_analog and (not field.centerdelta or field.centerdelta == 0) then
+				emu.print_error("Port '" .. port_name .."' " .. field_msg)
+				return nil
+			end
+			return field
+		end
+
+		local function release_pointer(pointer_id)
+			if pointers[pointer_id] then
+				local field = widgets[pointers[pointer_id].selected_widget].field
+				if field.is_analog then
+					field:clear_value()
+				end
+			end
+			pointers[pointer_id] = nil
+		end
+
+		local function pointer_updated(type, id, dev, x, y, btn, dn, up, cnt)
+			-- If a button is not pressed, reset the state of the current pointer.
+			if btn & 1 == 0 then
+				release_pointer(id)
+				return
+			end
+
+			-- If a button was just pressed, find the affected widget, if any.
+			if dn & 1 ~= 0 then
+				for i = 1, #widgets do
+					local found, relative
+					if widgets[i].slider_knob and widgets[i].slider_knob.bounds:includes(x, y) then
+						found = true
+						relative = true
+					elseif widgets[i].clickarea.bounds:includes(x, y) then
+						found = true
+						relative = false
+					end
+					if found then
+						pointers[id] = {
+							selected_widget = i,
+							relative = relative,
+							start_x = x,
+							start_y = y,
+							start_value = widgets[i].field.port:read() }
+						break
+					end
+				end
+			end
+
+			-- If there is no widget selected by the current pointer, we are done.
+			if pointers[id] == nil then
+				return
+			end
+
+			-- A widget is selected. Update its state based on the pointer's position.
+
+			local pointer = pointers[id]
+			local widget = widgets[pointer.selected_widget]
+
+			local min_value = widget.field.minvalue
+			local max_value = widget.field.maxvalue
+			local value_range = max_value - min_value
+
+			local new_value
+			if widget.is_knob then
+				if widget.is_horizontal then
+					local step_x = value_range / (widget.scale * widget.clickarea.bounds.width)
+					new_value = pointer.start_value + (x - pointer.start_x) * step_x
+				else
+					local step_y = value_range / (widget.scale * widget.clickarea.bounds.height)
+					new_value = pointer.start_value + (pointer.start_y - y) * step_y
+				end
+			else
+				local knob_half_height = widget.slider_knob.bounds.height / 2
+				local min_y = widget.clickarea.bounds.y0 + knob_half_height
+				local max_y = widget.clickarea.bounds.y1 - knob_half_height
+
+				if pointer.relative then
+					-- User clicked on the knob. The new value will depend on how
+					--  much the knob was dragged.
+					new_value = pointer.start_value - value_range * (y - pointer.start_y) / (max_y - min_y)
+				else
+					-- User clicked elsewhere on the slider. The new value will depend on
+					-- the absolute position of the click.
+					new_value = max_value - value_range * (y - min_y) / (max_y - min_y)
+				end
+			end
+
+			new_value = math.floor(new_value + 0.5)
+			if new_value < min_value then new_value = min_value end
+			if new_value > max_value then new_value = max_value end
+
+			if widget.field.is_analog then
+				widget.field:set_value(new_value)
+			else
+				widget.field.user_value = new_value
+			end
+		end
+
+		local function pointer_left(type, id, dev, x, y, up, cnt)
+			release_pointer(id)
+		end
+
+		local function pointer_aborted(type, id, dev, x, y, up, cnt)
+			release_pointer(id)
+		end
+
+		local function forget_pointers()
+			for id, pointer in pairs(pointers) do
+				release_pointer(id)
+			end
+			pointers = {}
+		end
+
+		function install_slider_callbacks(view)
+			view:set_pointer_updated_callback(pointer_updated)
+			view:set_pointer_left_callback(pointer_left)
+			view:set_pointer_aborted_callback(pointer_aborted)
+			view:set_forget_pointers_callback(forget_pointers)
+		end
+		-----------------------------------------------------------------------
+		-- Slider and knob library ends.
+		-----------------------------------------------------------------------
+	]]></script>
+
 </mamelayout>