mcs51.cpp: Eliminate atrocious hack for breaking out of INT0 polling loops (nw)

src/devices/cpu/mcs51/mcs51.cpp

@@ -1770,10 +1770,6 @@ void mcs51_cpu_device::check_irqs()
 		return;
 	}
 
-	/* also break out of jb int0,<self> loops */
-	if (ROP(PC) == 0x20 && ROP_ARG(PC+1) == 0xb2 && ROP_ARG(PC+2) == 0xfd)
-		PC += 3;
-
 	//Save current pc to stack, set pc to new interrupt vector
 	push_pc();
 	PC = int_vec;

src/mame/drivers/segas16a.cpp

@@ -570,32 +570,19 @@ READ8_MEMBER( segas16a_state::mcu_io_r )
 //**************************************************************************
 
 //-------------------------------------------------
-//  mcu_irq_assert - signal an interrupt to the
+//  i8751_main_cpu_vblank_w - if we have a fake
-//  I8751 MCU, and boost interleave to ensure
-//  good synchronization with the main CPU
-//-------------------------------------------------
-
-INTERRUPT_GEN_MEMBER( segas16a_state::mcu_irq_assert )
-{
-	// toggle the INT0 line on the MCU
-	m_mcu->set_input_line(MCS51_INT0_LINE, ASSERT_LINE);
-	m_mcu->set_input_line(MCS51_INT0_LINE, CLEAR_LINE);
-
-	// boost interleave to ensure that the MCU can break the M68000 out of a STOP
-	machine().scheduler().boost_interleave(attotime::zero, attotime::from_usec(100));
-}
-
-
-//-------------------------------------------------
-//  i8751_main_cpu_vblank - if we have a fake
 //  handler, we hook this to execute it
 //-------------------------------------------------
 
-INTERRUPT_GEN_MEMBER( segas16a_state::i8751_main_cpu_vblank )
+WRITE_LINE_MEMBER(segas16a_state::i8751_main_cpu_vblank_w)
 {
 	// if we have a fake 8751 handler, call it on VBLANK
-	if (!m_i8751_vblank_hook.isnull())
+	if (state && !m_i8751_vblank_hook.isnull())
 		m_i8751_vblank_hook();
+
+	// if we have a 8751, toggle the INT0 line on the MCU
+	if (m_mcu.found())
+		m_mcu->set_input_line(MCS51_INT0_LINE, state);
 }
 
 
@@ -2060,12 +2047,14 @@ MACHINE_CONFIG_END
 MACHINE_CONFIG_START(segas16a_state::system16a_i8751)
 	system16a(config);
 	MCFG_DEVICE_MODIFY("maincpu")
-	MCFG_DEVICE_VBLANK_INT_DRIVER("screen", segas16a_state, i8751_main_cpu_vblank)
+	MCFG_DEVICE_VBLANK_INT_REMOVE()
 
 	MCFG_DEVICE_ADD("mcu", I8751, 8000000)
 	MCFG_DEVICE_IO_MAP(mcu_io_map)
 	MCFG_MCS51_PORT_P1_OUT_CB(WRITE8(*this, segas16a_state, mcu_control_w))
-	MCFG_DEVICE_VBLANK_INT_DRIVER("screen", segas16a_state, mcu_irq_assert)
+
+	MCFG_SCREEN_MODIFY("screen")
+	MCFG_SCREEN_VBLANK_CALLBACK(WRITELINE(*this, segas16a_state, i8751_main_cpu_vblank_w))
 MACHINE_CONFIG_END
 
 

src/mame/drivers/system1.cpp

@@ -583,6 +583,11 @@ WRITE8_MEMBER(system1_state::mcu_control_w)
 	    Bit 1 -> n/c
 	    Bit 0 -> Directly connected to Z80 /INT line
 	*/
+
+	/* boost interleave to ensure that the MCU can break the Z80 out of a HALT */
+	if (!BIT(m_mcu_control, 6) && BIT(data, 6))
+		machine().scheduler().boost_interleave(attotime::zero, attotime::from_usec(10));
+
 	m_mcu_control = data;
 	m_maincpu->set_input_line(INPUT_LINE_HALT, (data & 0x40) ? ASSERT_LINE : CLEAR_LINE);
 	m_maincpu->set_input_line(0, (data & 0x01) ? CLEAR_LINE : ASSERT_LINE);
@@ -630,17 +635,6 @@ READ8_MEMBER(system1_state::mcu_io_r)
 }
 
 
-INTERRUPT_GEN_MEMBER(system1_state::mcu_irq_assert)
-{
-	/* toggle the INT0 line on the MCU */
-	device.execute().set_input_line(MCS51_INT0_LINE, ASSERT_LINE);
-	device.execute().set_input_line(MCS51_INT0_LINE, CLEAR_LINE);
-
-	/* boost interleave to ensure that the MCU can break the Z80 out of a HALT */
-	machine().scheduler().boost_interleave(attotime::zero, attotime::from_usec(10));
-}
-
-
 TIMER_DEVICE_CALLBACK_MEMBER(system1_state::mcu_t0_callback)
 {
 	/* The T0 line is clocked by something; if it is not clocked fast
@@ -2455,7 +2449,11 @@ MACHINE_CONFIG_START(system1_state::mcu)
 	MCFG_DEVICE_ADD("mcu", I8751, SOUND_CLOCK)
 	MCFG_DEVICE_IO_MAP(mcu_io_map)
 	MCFG_MCS51_PORT_P1_OUT_CB(WRITE8(*this, system1_state, mcu_control_w))
-	MCFG_DEVICE_VBLANK_INT_DRIVER("screen", system1_state, mcu_irq_assert)
+
+	MCFG_DEVICE_MODIFY("screen")
+	MCFG_SCREEN_VBLANK_CALLBACK(INPUTLINE("mcu", MCS51_INT0_LINE))
+	// This interrupt is driven by pin 15 of a PAL16R4 (315-5138 on Choplifter), based on the vertical count.
+	// The actual duty cycle likely differs from VBLANK, which is another output from the same PAL.
 
 	MCFG_TIMER_DRIVER_ADD_PERIODIC("mcu_t0", system1_state, mcu_t0_callback, attotime::from_usec(2500))
 MACHINE_CONFIG_END

src/mame/includes/segas16a.h

@@ -83,8 +83,7 @@ public:
 	DECLARE_READ8_MEMBER( mcu_io_r );
 
 	// I8751-related VBLANK interrupt handlers
-	INTERRUPT_GEN_MEMBER( mcu_irq_assert );
+	DECLARE_WRITE_LINE_MEMBER(i8751_main_cpu_vblank_w);
-	INTERRUPT_GEN_MEMBER( i8751_main_cpu_vblank );
 
 	// game-specific driver init
 	DECLARE_DRIVER_INIT(generic);

src/mame/includes/system1.h

@@ -119,7 +119,6 @@ public:
 	uint32_t screen_update_system1(screen_device &screen, bitmap_ind16 &bitmap, const rectangle &cliprect);
 	uint32_t screen_update_system2(screen_device &screen, bitmap_ind16 &bitmap, const rectangle &cliprect);
 	uint32_t screen_update_system2_rowscroll(screen_device &screen, bitmap_ind16 &bitmap, const rectangle &cliprect);
-	INTERRUPT_GEN_MEMBER(mcu_irq_assert);
 	TIMER_DEVICE_CALLBACK_MEMBER(soundirq_gen);
 	TIMER_DEVICE_CALLBACK_MEMBER(mcu_t0_callback);
 	DECLARE_WRITE8_MEMBER(system1_videoram_bank_w);