m6502: put back get_cycle() since OG says it'll be needed in future, but compile-time disable the slow precalculation/caching (nw)

src/emu/cpu/m6502/m6502.c

@@ -129,6 +129,7 @@ void m6502_device::init()
 	inst_substate = 0;
 	inst_state_base = 0;
 	sync = false;
+	end_cycles = 0;
 	inhibit_interrupts = false;
 }
 
@@ -142,6 +143,7 @@ void m6502_device::device_reset()
 	apu_irq_state = false;
 	irq_taken = false;
 	v_state = false;
+	end_cycles = 0;
 	sync = false;
 	sync_w(CLEAR_LINE);
 	inhibit_interrupts = false;
@@ -398,8 +400,18 @@ UINT8 m6502_device::do_asr(UINT8 v)
 	return v;
 }
 
+UINT64 m6502_device::get_cycle()
+{
+	return end_cycles == 0 || icount <= 0 ? machine().time().as_ticks(clock()) : end_cycles - icount;
+}
+
 void m6502_device::execute_run()
 {
+	// get_cycle() is currently unused, and this precalculation
+	// enormously slows down drivers with high interleave
+#if 0
+	end_cycles = machine().time().as_ticks(clock()) + icount;
+#endif
 	if(inst_substate)
 		do_exec_partial();
 
@@ -412,6 +424,7 @@ void m6502_device::execute_run()
 		}
 		do_exec_full();
 	}
+	end_cycles = 0;
 }
 
 void m6502_device::execute_set_input(int inputnum, int state)

src/emu/cpu/m6502/m6502.h

@@ -61,6 +61,7 @@ public:
 	DECLARE_WRITE_LINE_MEMBER( irq_line );
 	DECLARE_WRITE_LINE_MEMBER( nmi_line );
 
+	UINT64 get_cycle();
 	bool get_sync() const { return sync; }
 	void disable_direct() { direct_disabled = true; }
 
@@ -200,6 +201,7 @@ protected:
 	int icount;
 	bool nmi_state, irq_state, apu_irq_state, v_state;
 	bool irq_taken, sync, direct_disabled, inhibit_interrupts;
+	UINT64 end_cycles;
 
 	static const disasm_entry disasm_entries[0x100];
 

src/emu/cpu/m6502/m740.c

@@ -77,6 +77,7 @@ void m740_device::device_reset()
 	apu_irq_state = false;
 	irq_taken = false;
 	v_state = false;
+	end_cycles = 0;
 	sync = false;
 	inhibit_interrupts = false;
 	SP = 0x00ff;