a2bus, spectrum/exp: set a better example (nw)

src/devices/bus/a2bus/a2alfam2.cpp

@@ -101,8 +101,6 @@ a2bus_aesms_device::a2bus_aesms_device(const machine_config &mconfig, const char
 
 void a2bus_sn76489_device::device_start()
 {
-	// set_a2bus_device makes m_slot valid
-	set_a2bus_device();
 	m_latch0 = m_latch1 = m_latch2 = m_latch3 = 0;
 
 	save_item(NAME(m_latch0));

src/devices/bus/a2bus/a2applicard.cpp

@@ -87,9 +87,6 @@ a2bus_applicard_device::a2bus_applicard_device(const machine_config &mconfig, co
 
 void a2bus_applicard_device::device_start()
 {
-	// set_a2bus_device makes m_slot valid
-	set_a2bus_device();
-
 	// locate Z80 ROM
 	m_z80rom = device().machine().root_device().memregion(this->subtag(Z80_ROM_REGION).c_str())->base();
 

src/devices/bus/a2bus/a2arcadebd.cpp

@@ -71,8 +71,6 @@ a2bus_arcboard_device::a2bus_arcboard_device(const machine_config &mconfig, devi
 
 void a2bus_arcboard_device::device_start()
 {
-	// set_a2bus_device makes m_slot valid
-	set_a2bus_device();
 }
 
 void a2bus_arcboard_device::device_reset()

src/devices/bus/a2bus/a2bus.cpp

@@ -307,22 +307,30 @@ device_a2bus_card_interface::~device_a2bus_card_interface()
 void device_a2bus_card_interface::static_set_a2bus_tag(device_t &device, const char *tag, const char *slottag)
 {
 	device_a2bus_card_interface &a2bus_card = dynamic_cast<device_a2bus_card_interface &>(device);
+	assert(a2bus_card);
 	a2bus_card.m_a2bus_tag = tag;
 	a2bus_card.m_a2bus_slottag = slottag;
 }
 
-void device_a2bus_card_interface::set_a2bus_device()
+void device_a2bus_card_interface::interface_pre_start()
 {
-	// extract the slot number from the last digit of the slot tag
-	int tlen = strlen(m_a2bus_slottag);
-
-	m_slot = (m_a2bus_slottag[tlen-1] - '0');
-
-	if (m_slot < 0 || m_slot > 7)
+	if (!m_a2bus)
 	{
-		fatalerror("Slot %x out of range for Apple II Bus\n", m_slot);
-	}
+		// extract the slot number from the last digit of the slot tag
+		size_t const tlen = strlen(m_a2bus_slottag);
 
-	m_a2bus = dynamic_cast<a2bus_device *>(device().machine().device(m_a2bus_tag));
-	m_a2bus->add_a2bus_card(m_slot, this);
+		m_slot = (m_a2bus_slottag[tlen-1] - '0');
+		if (m_slot < 0 || m_slot > 7)
+			fatalerror("Slot %x out of range for Apple II Bus\n", m_slot);
+
+		device_t *const bus = device().machine().device(m_a2bus_tag);
+		if (!bus)
+			fatalerror("Can't find Apple II Bus device %s\n", m_a2bus_tag);
+
+		m_a2bus = dynamic_cast<a2bus_device *>(bus);
+		if (!m_a2bus)
+			fatalerror("Device %s (%s) is not an instance of a2bus_device\n", bus->tag(), bus->name());
+
+		m_a2bus->add_a2bus_card(m_slot, this);
+	}
 }

src/devices/bus/a2bus/a2bus.h

@@ -67,14 +67,14 @@ public:
 	// construction/destruction
 	a2bus_slot_device(const machine_config &mconfig, const char *tag, device_t *owner, uint32_t clock);
 
-	// device-level overrides
-	virtual void device_start() override;
-
 	// inline configuration
 	static void static_set_a2bus_slot(device_t &device, const char *tag, const char *slottag);
 protected:
 	a2bus_slot_device(const machine_config &mconfig, device_type type, const char *tag, device_t *owner, uint32_t clock);
 
+	// device-level overrides
+	virtual void device_start() override;
+
 	// configuration
 	const char *m_a2bus_tag, *m_a2bus_slottag;
 };
@@ -84,6 +84,7 @@ DECLARE_DEVICE_TYPE(A2BUS_SLOT, a2bus_slot_device)
 
 
 class device_a2bus_card_interface;
+
 // ======================> a2bus_device
 class a2bus_device : public device_t
 {
@@ -167,8 +168,6 @@ public:
 
 	device_a2bus_card_interface *next() const { return m_next; }
 
-	void set_a2bus_device();
-
 	uint32_t get_slotromspace() { return 0xc000 | (m_slot<<8); }      // return Cn00 address for this slot
 	uint32_t get_slotiospace() { return 0xc080 + (m_slot<<4); }       // return C0n0 address for this slot
 
@@ -194,6 +193,12 @@ public:
 protected:
 	device_a2bus_card_interface(const machine_config &mconfig, device_t &device);
 
+	virtual void interface_pre_start() override;
+
+	int slotno() const { assert(m_a2bus); return m_slot; }
+	a2bus_device &a2bus() { assert(m_a2bus); return *m_a2bus; }
+
+private:
 	a2bus_device  *m_a2bus;
 	const char *m_a2bus_tag, *m_a2bus_slottag;
 	int m_slot;

src/devices/bus/a2bus/a2cffa.cpp

@@ -102,9 +102,6 @@ a2bus_cffa2_6502_device::a2bus_cffa2_6502_device(const machine_config &mconfig,
 
 void a2bus_cffa2000_device::device_start()
 {
-	// set_a2bus_device makes m_slot valid
-	set_a2bus_device();
-
 	m_rom = device().machine().root_device().memregion(this->subtag(CFFA2_ROM_REGION).c_str())->base();
 
 	// patch default setting so slave device is enabled and up to 13 devices on both connectors
@@ -216,7 +213,7 @@ void a2bus_cffa2000_device::write_c0nx(uint8_t offset, uint8_t data)
 
 uint8_t a2bus_cffa2000_device::read_cnxx(uint8_t offset)
 {
-	int slotimg = m_slot * 0x100;
+	int const slotimg = slotno() * 0x100;
 
 	// ROM contains a CnXX image for each of slots 1-7
 	return m_eeprom[offset+slotimg];

src/devices/bus/a2bus/a2corvus.cpp

@@ -114,9 +114,6 @@ a2bus_corvus_device::a2bus_corvus_device(const machine_config &mconfig, const ch
 
 void a2bus_corvus_device::device_start()
 {
-	// set_a2bus_device makes m_slot valid
-	set_a2bus_device();
-
 	m_rom = device().machine().root_device().memregion(this->subtag(CORVUS_ROM_REGION).c_str())->base();
 }
 

src/devices/bus/a2bus/a2diskii.cpp

@@ -117,9 +117,6 @@ a2bus_agat7flop_device::a2bus_agat7flop_device(const machine_config &mconfig, co
 
 void a2bus_floppy_device::device_start()
 {
-	// set_a2bus_device makes m_slot valid
-	set_a2bus_device();
-
 	m_rom = device().machine().root_device().memregion(this->subtag(DISKII_ROM_REGION).c_str())->base();
 }
 

src/devices/bus/a2bus/a2diskiing.cpp

@@ -78,9 +78,6 @@ a2bus_diskiing_device::a2bus_diskiing_device(const machine_config &mconfig, cons
 
 void a2bus_diskiing_device::device_start()
 {
-	// set_a2bus_device makes m_slot valid
-	set_a2bus_device();
-
 	m_rom = device().machine().root_device().memregion(this->subtag(DISKII_ROM_REGION).c_str())->base();
 }
 

src/devices/bus/a2bus/a2dx1.cpp

@@ -63,8 +63,6 @@ a2bus_dx1_device::a2bus_dx1_device(const machine_config &mconfig, const char *ta
 
 void a2bus_dx1_device::device_start()
 {
-	// set_a2bus_device makes m_slot valid
-	set_a2bus_device();
 }
 
 uint8_t a2bus_dx1_device::read_c0nx(uint8_t offset)

src/devices/bus/a2bus/a2echoii.cpp

@@ -61,8 +61,6 @@ a2bus_echoii_device::a2bus_echoii_device(const machine_config &mconfig, const ch
 
 void a2bus_echoii_device::device_start()
 {
-	// set_a2bus_device makes m_slot valid
-	set_a2bus_device();
 }
 
 void a2bus_echoii_device::device_reset()

src/devices/bus/a2bus/a2hsscsi.cpp

@@ -129,9 +129,6 @@ a2bus_hsscsi_device::a2bus_hsscsi_device(const machine_config &mconfig, const ch
 
 void a2bus_hsscsi_device::device_start()
 {
-	// set_a2bus_device makes m_slot valid
-	set_a2bus_device();
-
 	m_rom = machine().root_device().memregion(this->subtag(SCSI_ROM_REGION).c_str())->base();
 
 	memset(m_ram, 0, 8192);

src/devices/bus/a2bus/a2mcms.cpp

@@ -81,8 +81,6 @@ a2bus_mcms1_device::a2bus_mcms1_device(const machine_config &mconfig, const char
 
 void a2bus_mcms1_device::device_start()
 {
-	// set_a2bus_device makes m_slot valid
-	set_a2bus_device();
 }
 
 void a2bus_mcms1_device::device_reset()
@@ -159,18 +157,13 @@ a2bus_mcms2_device::a2bus_mcms2_device(const machine_config &mconfig, const char
 
 void a2bus_mcms2_device::device_start()
 {
-	// set_a2bus_device makes m_slot valid
-	set_a2bus_device();
-
-	if (m_slot < 2)
-	{
+	if (slotno() < 2)
 		fatalerror("MCMS: Card 2 must be in slot 2 or greater\n");
-	}
 }
 
 void a2bus_mcms2_device::device_reset()
 {
-	m_card1 = static_cast<a2bus_mcms1_device *>(m_a2bus->m_device_list[m_slot-1]);
+	m_card1 = downcast<a2bus_mcms1_device *>(a2bus().m_device_list[slotno()-1]);
 	m_engine = m_card1->get_engine();
 }
 

src/devices/bus/a2bus/a2memexp.cpp

@@ -95,9 +95,6 @@ a2bus_ramfactor_device::a2bus_ramfactor_device(const machine_config &mconfig, co
 
 void a2bus_memexp_device::device_start()
 {
-	// set_a2bus_device makes m_slot valid
-	set_a2bus_device();
-
 	m_rom = device().machine().root_device().memregion(this->subtag(MEMEXP_ROM_REGION).c_str())->base();
 
 	memset(m_ram, 0xff, 1024*1024*sizeof(uint8_t));
@@ -193,15 +190,13 @@ void a2bus_memexp_device::write_c0nx(uint8_t offset, uint8_t data)
 
 uint8_t a2bus_memexp_device::read_cnxx(uint8_t offset)
 {
-	int slotimg = m_slot * 0x100;
+	int const slotimg = slotno() * 0x100;
 
 	// first 0x400 of ROM contains a CnXX image for each of slots 1-7, last 0x400 is c800 image
 	if ((m_isramfactor) && (m_regs[0xf] & 0x01))
-	{
 		return m_rom[offset+slotimg+0x1000];
-	}
-
-	return m_rom[offset+slotimg];
+	else
+		return m_rom[offset+slotimg];
 }
 
 /*-------------------------------------------------
@@ -212,9 +207,7 @@ uint8_t a2bus_memexp_device::read_c800(uint16_t offset)
 {
 	// c70a diags confirm: bit 1 of cn0F banks in the second half of the ROM
 	if ((m_isramfactor) && (m_regs[0xf] & 0x01))
-	{
 		return m_rom[offset+0x1800];
-	}
-
-	return m_rom[offset+0x800];
+	else
+		return m_rom[offset+0x800];
 }

src/devices/bus/a2bus/a2midi.cpp

@@ -74,8 +74,6 @@ a2bus_midi_device::a2bus_midi_device(const machine_config &mconfig, device_type
 
 void a2bus_midi_device::device_start()
 {
-	// set_a2bus_device makes m_slot valid
-	set_a2bus_device();
 }
 
 void a2bus_midi_device::device_reset()

src/devices/bus/a2bus/a2mockingboard.cpp

@@ -145,9 +145,6 @@ a2bus_echoplus_device::a2bus_echoplus_device(const machine_config &mconfig, cons
 
 void a2bus_ayboard_device::device_start()
 {
-	// set_a2bus_device makes m_slot valid
-	set_a2bus_device();
-
 	save_item(NAME(m_porta1));
 	save_item(NAME(m_porta2));
 }
@@ -250,7 +247,7 @@ void a2bus_ayboard_device::write_cnxx(uint8_t offset, uint8_t data)
 		}
 		else
 		{
-			logerror("Mockingboard(%d): unk write %02x to Cn%02X (%s)\n", m_slot, data, offset, machine().describe_context());
+			logerror("Mockingboard(%d): unk write %02x to Cn%02X (%s)\n", slotno(), data, offset, machine().describe_context());
 		}
 	}
 }

src/devices/bus/a2bus/a2pic.cpp

@@ -115,9 +115,6 @@ a2bus_pic_device::a2bus_pic_device(const machine_config &mconfig, device_type ty
 
 void a2bus_pic_device::device_start()
 {
-	// set_a2bus_device makes m_slot valid
-	set_a2bus_device();
-
 	m_rom = device().machine().root_device().memregion(this->subtag(PIC_ROM_REGION).c_str())->base();
 
 	m_timer = timer_alloc(0, nullptr);

src/devices/bus/a2bus/a2sam.cpp

@@ -55,8 +55,6 @@ a2bus_sam_device::a2bus_sam_device(const machine_config &mconfig, const char *ta
 
 void a2bus_sam_device::device_start()
 {
-	// set_a2bus_device makes m_slot valid
-	set_a2bus_device();
 }
 
 void a2bus_sam_device::device_reset()

src/devices/bus/a2bus/a2scsi.cpp

@@ -122,9 +122,6 @@ a2bus_scsi_device::a2bus_scsi_device(const machine_config &mconfig, const char *
 
 void a2bus_scsi_device::device_start()
 {
-	// set_a2bus_device makes m_slot valid
-	set_a2bus_device();
-
 	m_rom = device().machine().root_device().memregion(this->subtag(SCSI_ROM_REGION).c_str())->base();
 
 	memset(m_ram, 0, 8192);

src/devices/bus/a2bus/a2softcard.cpp

@@ -63,9 +63,6 @@ a2bus_softcard_device::a2bus_softcard_device(const machine_config &mconfig, cons
 
 void a2bus_softcard_device::device_start()
 {
-	// set_a2bus_device makes m_slot valid
-	set_a2bus_device();
-
 	save_item(NAME(m_bEnabled));
 	save_item(NAME(m_FirstZ80Boot));
 }

src/devices/bus/a2bus/a2ssc.cpp

@@ -143,9 +143,6 @@ a2bus_ssc_device::a2bus_ssc_device(const machine_config &mconfig, device_type ty
 
 void a2bus_ssc_device::device_start()
 {
-	// set_a2bus_device makes m_slot valid
-	set_a2bus_device();
-
 	m_rom = machine().root_device().memregion(this->subtag(SSC_ROM_REGION).c_str())->base();
 }
 

src/devices/bus/a2bus/a2swyft.cpp

@@ -61,9 +61,6 @@ a2bus_swyft_device::a2bus_swyft_device(const machine_config &mconfig, device_typ
 
 void a2bus_swyft_device::device_start()
 {
-	// set_a2bus_device makes m_slot valid
-	set_a2bus_device();
-
 	m_rom = device().machine().root_device().memregion(this->subtag(SWYFT_ROM_REGION).c_str())->base();
 
 	save_item(NAME(m_rombank));

src/devices/bus/a2bus/a2themill.cpp

@@ -79,9 +79,6 @@ a2bus_themill_device::a2bus_themill_device(const machine_config &mconfig, const
 
 void a2bus_themill_device::device_start()
 {
-	// set_a2bus_device makes m_slot valid
-	set_a2bus_device();
-
 	save_item(NAME(m_bEnabled));
 	save_item(NAME(m_flipAddrSpace));
 	save_item(NAME(m_6809Mode));

src/devices/bus/a2bus/a2thunderclock.cpp

@@ -89,9 +89,6 @@ a2bus_thunderclock_device::a2bus_thunderclock_device(const machine_config &mconf
 
 void a2bus_thunderclock_device::device_start()
 {
-	// set_a2bus_device makes m_slot valid
-	set_a2bus_device();
-
 	m_rom = device().machine().root_device().memregion(this->subtag(THUNDERCLOCK_ROM_REGION).c_str())->base();
 
 	save_item(NAME(m_dataout));

src/devices/bus/a2bus/a2ultraterm.cpp

@@ -157,9 +157,6 @@ a2bus_ultratermenh_device::a2bus_ultratermenh_device(const machine_config &mconf
 
 void a2bus_videx160_device::device_start()
 {
-	// set_a2bus_device makes m_slot valid
-	set_a2bus_device();
-
 	m_rom = machine().root_device().memregion(this->subtag(ULTRATERM_ROM_REGION).c_str())->base();
 
 	m_chrrom = machine().root_device().memregion(this->subtag(ULTRATERM_GFX_REGION).c_str())->base();
@@ -256,7 +253,7 @@ void a2bus_videx160_device::write_c0nx(uint8_t offset, uint8_t data)
 
 uint8_t a2bus_videx160_device::read_cnxx(uint8_t offset)
 {
-	return m_rom[offset+(m_slot * 0x100)];
+	return m_rom[offset+(slotno() * 0x100)];
 }
 
 /*-------------------------------------------------

src/devices/bus/a2bus/a2videoterm.cpp

@@ -211,9 +211,6 @@ a2bus_aevm80_device::a2bus_aevm80_device(const machine_config &mconfig, const ch
 
 void a2bus_videx80_device::device_start()
 {
-	// set_a2bus_device makes m_slot valid
-	set_a2bus_device();
-
 	m_rom = device().machine().root_device().memregion(this->subtag(VIDEOTERM_ROM_REGION).c_str())->base();
 
 	m_chrrom = device().machine().root_device().memregion(this->subtag(VIDEOTERM_GFX_REGION).c_str())->base();

src/devices/bus/a2bus/a2vulcan.cpp

@@ -131,9 +131,6 @@ a2bus_vulcangold_device::a2bus_vulcangold_device(const machine_config &mconfig,
 
 void a2bus_vulcanbase_device::device_start()
 {
-	// set_a2bus_device makes m_slot valid
-	set_a2bus_device();
-
 	m_rom = device().machine().root_device().memregion(this->subtag(VULCAN_ROM_REGION).c_str())->base();
 
 	save_item(NAME(m_lastdata));
@@ -262,7 +259,7 @@ void a2bus_vulcanbase_device::write_c0nx(uint8_t offset, uint8_t data)
 
 uint8_t a2bus_vulcanbase_device::read_cnxx(uint8_t offset)
 {
-	int slotimg = m_slot * 0x100;
+	int const slotimg = slotno() * 0x100;
 
 	// ROM contains a CnXX image for each of slots 1-7 at 0x3400
 	return m_rom[offset+slotimg+0x3400];

src/devices/bus/a2bus/a2zipdrive.cpp

@@ -81,9 +81,6 @@ a2bus_zipdrive_device::a2bus_zipdrive_device(const machine_config &mconfig, cons
 
 void a2bus_zipdrivebase_device::device_start()
 {
-	// set_a2bus_device makes m_slot valid
-	set_a2bus_device();
-
 	m_rom = device().machine().root_device().memregion(this->subtag(ZIPDRIVE_ROM_REGION).c_str())->base();
 
 	save_item(NAME(m_lastdata));
@@ -174,7 +171,7 @@ void a2bus_zipdrivebase_device::write_c0nx(uint8_t offset, uint8_t data)
 
 uint8_t a2bus_zipdrivebase_device::read_cnxx(uint8_t offset)
 {
-	int slotimg = m_slot * 0x100;
+	int const slotimg = slotno() * 0x100;
 
 	// ROM contains CnXX images for each of slots 1-7 at 0x0 and 0x1000
 	return m_rom[offset+slotimg+0x1000];

src/devices/bus/a2bus/agat7langcard.cpp

@@ -48,9 +48,6 @@ a2bus_agat7langcard_device::a2bus_agat7langcard_device(const machine_config &mco
 
 void a2bus_agat7langcard_device::device_start()
 {
-	// set_a2bus_device makes m_slot valid
-	set_a2bus_device();
-
 	memset(m_ram, 0, 32 * 1024);
 
 	save_item(NAME(m_inh_state));

src/devices/bus/a2bus/agat7ram.cpp

@@ -48,9 +48,6 @@ a2bus_agat7ram_device::a2bus_agat7ram_device(const machine_config &mconfig, cons
 
 void a2bus_agat7ram_device::device_start()
 {
-	// set_a2bus_device makes m_slot valid
-	set_a2bus_device();
-
 	memset(m_ram, 0, 32 * 1024);
 
 	save_item(NAME(m_inh_state));

src/devices/bus/a2bus/agat840k_hle.cpp

@@ -133,9 +133,6 @@ void a2bus_agat840k_hle_device::index_callback(int unit, int state)
 
 void a2bus_agat840k_hle_device::device_start()
 {
-	// set_a2bus_device makes m_slot valid
-	set_a2bus_device();
-
 	m_rom = device().machine().root_device().memregion(this->subtag(AGAT840K_ROM_REGION).c_str())->base();
 
 	m_mxcs = MXCSR_SYNC;

src/devices/bus/a2bus/corvfdc01.cpp

@@ -128,9 +128,6 @@ a2bus_corvfdc01_device::a2bus_corvfdc01_device(const machine_config &mconfig, co
 
 void a2bus_corvfdc01_device::device_start()
 {
-	// set_a2bus_device makes m_slot valid
-	set_a2bus_device();
-
 	m_rom = device().machine().root_device().memregion(this->subtag(FDC01_ROM_REGION).c_str())->base();
 
 	save_item(NAME(m_fdc_local_status));

src/devices/bus/a2bus/corvfdc02.cpp

@@ -96,9 +96,6 @@ a2bus_corvfdc02_device::a2bus_corvfdc02_device(const machine_config &mconfig, co
 
 void a2bus_corvfdc02_device::device_start()
 {
-	// set_a2bus_device makes m_slot valid
-	set_a2bus_device();
-
 	m_rom = device().machine().root_device().memregion(this->subtag(FDC02_ROM_REGION).c_str())->base();
 
 	m_timer = timer_alloc(0);

src/devices/bus/a2bus/ezcgi.cpp

@@ -120,8 +120,6 @@ a2bus_ezcgi_9958_device::a2bus_ezcgi_9958_device(const machine_config &mconfig,
 
 void a2bus_ezcgi_device::device_start()
 {
-	// set_a2bus_device makes m_slot valid
-	set_a2bus_device();
 }
 
 void a2bus_ezcgi_device::device_reset()
@@ -130,8 +128,6 @@ void a2bus_ezcgi_device::device_reset()
 
 void a2bus_ezcgi_9938_device::device_start()
 {
-	// set_a2bus_device makes m_slot valid
-	set_a2bus_device();
 }
 
 void a2bus_ezcgi_9938_device::device_reset()
@@ -140,8 +136,6 @@ void a2bus_ezcgi_9938_device::device_reset()
 
 void a2bus_ezcgi_9958_device::device_start()
 {
-	// set_a2bus_device makes m_slot valid
-	set_a2bus_device();
 }
 
 void a2bus_ezcgi_9958_device::device_reset()

src/devices/bus/a2bus/laser128.cpp

@@ -11,6 +11,9 @@
 #include "emu.h"
 #include "laser128.h"
 
+//#define VERBOSE 1
+#include "logmacro.h"
+
 /***************************************************************************
     PARAMETERS
 ***************************************************************************/
@@ -54,9 +57,6 @@ a2bus_laser128_device::a2bus_laser128_device(const machine_config &mconfig, cons
 
 void a2bus_laser128_device::device_start()
 {
-	// set_a2bus_device makes m_slot valid
-	set_a2bus_device();
-
 	save_item(NAME(m_slot7_bank));
 	save_item(NAME(m_slot7_ram_bank));
 }
@@ -79,12 +79,12 @@ void a2bus_laser128_device::write_c0nx(uint8_t offset, uint8_t data)
 
 uint8_t a2bus_laser128_device::read_cnxx(uint8_t offset)
 {
-	return m_rom[offset + (m_slot * 0x100) + 0x4000];
+	return m_rom[offset + (slotno() * 0x100) + 0x4000];
 }
 
 uint8_t a2bus_laser128_device::read_c800(uint16_t offset)
 {
-	switch (m_slot)
+	switch (slotno())
 	{
 		case 1:
 			return m_rom[(offset & 0x7ff) + 0x4800];
@@ -100,10 +100,9 @@ uint8_t a2bus_laser128_device::read_c800(uint16_t offset)
 
 		case 7:
 			if (offset < 0x400)
-			{
 				return m_slot7_ram[offset];
-			}
-			return m_rom[(offset & 0x3ff) + 0x6000 + m_slot7_bank];
+			else
+				return m_rom[(offset & 0x3ff) + 0x6000 + m_slot7_bank];
 	}
 
 	return 0xff;
@@ -111,29 +110,34 @@ uint8_t a2bus_laser128_device::read_c800(uint16_t offset)
 
 void a2bus_laser128_device::write_c800(uint16_t offset, uint8_t data)
 {
-	if ((m_slot == 7) && (offset < 0x400))
+	if ((slotno() == 7) && (offset < 0x400))
 	{
 		m_slot7_ram[offset] = data;
 	}
 
 	// UDCREG
-	if ((m_slot == 7) && (offset == 0x7f8))
+	if ((slotno() == 7) && (offset == 0x7f8))
 	{
-//      printf("%02x to UDCREG\n", data);
+		LOG("%02x to UDCREG\n", data);
 
 		m_slot7_ram_bank = (data & 0x8) ? 0x400 : 0;
 		m_slot7_bank = (((data >> 4) & 0x7) * 0x400);
 
-//      printf("\tRAM bank %x, ROM bank %x\n", m_slot7_ram_bank, m_slot7_bank);
+		LOG("\tRAM bank %x, ROM bank %x\n", m_slot7_ram_bank, m_slot7_bank);
 	}
 }
 
 bool a2bus_laser128_device::take_c800()
 {
-	if ((m_slot == 1) || (m_slot == 2) || (m_slot == 5) || (m_slot == 6) || (m_slot == 7))
+	switch (slotno())
 	{
-		return true;
+		case 1:
+		case 2:
+		case 5:
+		case 6:
+		case 7:
+			return true;
+		default:
+			return false;
 	}
-
-	return false;
 }

src/devices/bus/a2bus/mouse.cpp

@@ -180,9 +180,6 @@ a2bus_mouse_device::a2bus_mouse_device(const machine_config &mconfig, const char
 
 void a2bus_mouse_device::device_start()
 {
-	// set_a2bus_device makes m_slot valid
-	set_a2bus_device();
-
 	// register save state variables
 	save_item(NAME(m_port_a_in));
 	save_item(NAME(m_port_b_in));

src/devices/bus/a2bus/pc_xporter.cpp

@@ -202,9 +202,6 @@ a2bus_pcxporter_device::a2bus_pcxporter_device(const machine_config &mconfig, co
 
 void a2bus_pcxporter_device::device_start()
 {
-	// set_a2bus_device makes m_slot valid
-	set_a2bus_device();
-
 	memset(m_ram, 0, 768*1024);
 	memset(m_regs, 0, 0x400);
 	m_offset = 0;

src/devices/bus/a2bus/ramcard128k.cpp

@@ -46,9 +46,6 @@ a2bus_ssramcard_device::a2bus_ssramcard_device(const machine_config &mconfig, co
 
 void a2bus_ssramcard_device::device_start()
 {
-	// set_a2bus_device makes m_slot valid
-	set_a2bus_device();
-
 	memset(m_ram, 0, 128*1024);
 
 	save_item(NAME(m_inh_state));

src/devices/bus/a2bus/ramcard16k.cpp

@@ -46,9 +46,6 @@ a2bus_ramcard_device::a2bus_ramcard_device(const machine_config &mconfig, const
 
 void a2bus_ramcard_device::device_start()
 {
-	// set_a2bus_device makes m_slot valid
-	set_a2bus_device();
-
 	memset(m_ram, 0, 16*1024);
 
 	save_item(NAME(m_inh_state));

src/devices/bus/a2bus/ssbapple.cpp

@@ -62,13 +62,8 @@ a2bus_ssb_device::a2bus_ssb_device(const machine_config &mconfig, const char *ta
 
 void a2bus_ssb_device::device_start()
 {
-	// set_a2bus_device makes m_slot valid
-	set_a2bus_device();
-
-	if (m_slot != 2)
-	{
+	if (slotno() != 2)
 		popmessage("SSB Card should be in slot 2!\n");
-	}
 }
 
 void a2bus_ssb_device::device_reset()

src/devices/bus/a2bus/ssprite.cpp

@@ -71,8 +71,6 @@ a2bus_ssprite_device::a2bus_ssprite_device(const machine_config &mconfig, device
 
 void a2bus_ssprite_device::device_start()
 {
-	// set_a2bus_device makes m_slot valid
-	set_a2bus_device();
 }
 
 void a2bus_ssprite_device::device_reset()

src/devices/bus/a2bus/timemasterho.cpp

@@ -138,9 +138,6 @@ a2bus_timemasterho_device::a2bus_timemasterho_device(const machine_config &mconf
 
 void a2bus_timemasterho_device::device_start()
 {
-	// set_a2bus_device makes m_slot valid
-	set_a2bus_device();
-
 	m_rom = device().machine().root_device().memregion(this->subtag(TIMEMASTER_ROM_REGION).c_str())->base();
 }
 

src/devices/bus/a2bus/transwarp.cpp

@@ -151,9 +151,6 @@ a2bus_transwarp_device::a2bus_transwarp_device(const machine_config &mconfig, co
 
 void a2bus_transwarp_device::device_start()
 {
-	// set_a2bus_device makes m_slot valid
-	set_a2bus_device();
-
 	m_timer = timer_alloc(0);
 
 	save_item(NAME(m_bEnabled));

src/devices/bus/spectrum/exp.cpp

@@ -68,13 +68,27 @@ spectrum_expansion_slot_device::~spectrum_expansion_slot_device()
 }
 
 
+//-------------------------------------------------
+//  device_validity_check - device-specific checks
+//-------------------------------------------------
+
+void spectrum_expansion_slot_device::device_validity_check(validity_checker &valid) const
+{
+	device_t *const card(get_card_device());
+	if (card && !dynamic_cast<device_spectrum_expansion_interface *>(card))
+		osd_printf_error("Card device %s (%s) does not implement device_spectrum_expansion_interface\n", card->tag(), card->name());
+}
+
 //-------------------------------------------------
 //  device_start - device-specific startup
 //-------------------------------------------------
 
 void spectrum_expansion_slot_device::device_start()
 {
-	m_card = dynamic_cast<device_spectrum_expansion_interface *>(get_card_device());
+	device_t *const card_device(get_card_device());
+	m_card = dynamic_cast<device_spectrum_expansion_interface *>(card_device);
+	if (card_device && !m_card)
+		throw emu_fatalerror("spectrum_expansion_slot_device: card device %s (%s) does not implement device_spectrum_expansion_interface\n", card_device->tag(), card_device->name());
 
 	// resolve callbacks
 	m_irq_handler.resolve_safe();
@@ -87,10 +101,6 @@ void spectrum_expansion_slot_device::device_start()
 
 void spectrum_expansion_slot_device::device_reset()
 {
-	if (get_card_device())
-	{
-		get_card_device()->reset();
-	}
 }
 
 //-------------------------------------------------

src/devices/bus/spectrum/exp.h

@@ -104,6 +104,7 @@ public:
 
 protected:
 	// device-level overrides
+	virtual void device_validity_check(validity_checker &valid) const override;
 	virtual void device_start() override;
 	virtual void device_reset() override;