--- Frodo4/Src/CPUC64_SC.cpp	2004/01/11 14:03:29	1.4
+++ Frodo4/Src/CPUC64_SC.cpp	2010/04/22 15:08:18	1.8
@@ -1,7 +1,7 @@
 /*
  *  CPUC64_SC.cpp - Single-cycle 6510 (C64) emulation
  *
- *  Frodo (C) 1994-1997,2002-2003 Christian Bauer
+ *  Frodo Copyright (C) Christian Bauer
  *
  *  This program is free software; you can redistribute it and/or modify
  *  it under the terms of the GNU General Public License as published by
@@ -103,6 +103,7 @@ MOS6510::MOS6510(C64 *c64, uint8 *Ram, u
 	dfff_byte = 0x55;
 	BALow = false;
 	first_irq_cycle = first_nmi_cycle = 0;
+	opflags = 0;
 }
 
 
@@ -179,6 +180,7 @@ void MOS6510::SetState(MOS6510State *s)
 
 	ddr = s->ddr;
 	pr = s->pr;
+	pr_out = 0;  // FIXME: should be saved in MOS6510State
 	new_config();
 
 	pc = s->pc;
@@ -201,7 +203,8 @@ void MOS6510::SetState(MOS6510State *s)
 
 void MOS6510::new_config(void)
 {
-	uint8 port = ~ddr | pr;
+	pr_out = (pr_out & ~ddr) | (pr & ddr);
+	uint8 port = pr | ~ddr;
 
 	basic_in = (port & 3) == 3;
 	kernal_in = port & 2;
@@ -279,12 +282,16 @@ inline uint8 MOS6510::read_byte_io(uint1
 uint8 MOS6510::read_byte(uint16 adr)
 {
 	if (adr < 0xa000) {
-		if (adr >= 2)
+		if (adr >= 2) {
 			return ram[adr];
-		else if (adr == 0)
+		} else if (adr == 0) {
 			return ddr;
-		else
-			return (ddr & pr) | (~ddr & 0x17);
+		} else {
+			uint8 byte = (pr | ~ddr) & (pr_out | 0x17);
+			if (!(ddr & 0x20))
+				byte &= 0xdf;
+			return byte;
+		}
 	} else
 		return read_byte_io(adr);
 }
@@ -294,7 +301,7 @@ uint8 MOS6510::read_byte(uint16 adr)
  *  $dfa0-$dfff: Emulator identification
  */
 
-const char frodo_id[0x5c] = "FRODO\r(C) 1994-1997 CHRISTIAN BAUER";
+const char frodo_id[0x5c] = "FRODO\r(C) CHRISTIAN BAUER";
 
 uint8 MOS6510::read_emulator_id(uint16 adr)
 {
@@ -546,12 +553,13 @@ void MOS6510::Reset(void)
 		ram[0x8004] = 0;
 
 	// Initialize extra 6510 registers and memory configuration
-	ddr = pr = 0;
+	ddr = pr = pr_out = 0;
 	new_config();
 
 	// Clear all interrupt lines
 	interrupt.intr_any = 0;
 	nmi_state = false;
+	opflags = 0;
 
 	// Read reset vector
 	pc = read_word(0xfffc);
@@ -596,13 +604,23 @@ void MOS6510::EmulateCycle(void)
 
 	// Any pending interrupts in state 0 (opcode fetch)?
 	if (!state && interrupt.intr_any) {
-		if (interrupt.intr[INT_RESET])
+		if (interrupt.intr[INT_RESET]) {
 			Reset();
-		else if (interrupt.intr[INT_NMI] && (the_c64->CycleCounter-first_nmi_cycle >= 2)) {
-			interrupt.intr[INT_NMI] = false;	// Simulate an edge-triggered input
-			state = 0x0010;
-		} else if ((interrupt.intr[INT_VICIRQ] || interrupt.intr[INT_CIAIRQ]) && (the_c64->CycleCounter-first_irq_cycle >= 2) && !i_flag)
-			state = 0x0008;
+		} else if (interrupt.intr[INT_NMI]) {
+			uint32 int_delay = (opflags & OPFLAG_INT_DELAYED) ? 1 : 0;  // Taken branches to the same page delay the NMI
+			if (the_c64->CycleCounter - first_nmi_cycle - int_delay >= 2) {
+				interrupt.intr[INT_NMI] = false;	// Simulate an edge-triggered input
+				state = 0x0010;
+				opflags = 0;
+			}
+		} else if ((interrupt.intr[INT_VICIRQ] || interrupt.intr[INT_CIAIRQ]) &&
+				   (!i_flag || (opflags & OPFLAG_IRQ_DISABLED)) && !(opflags & OPFLAG_IRQ_ENABLED)) {
+			uint32 int_delay = (opflags & OPFLAG_INT_DELAYED) ? 1 : 0;  // Taken branches to the same page delay the IRQ
+			if (the_c64->CycleCounter - first_irq_cycle - int_delay >= 2) {
+				state = 0x0008;
+				opflags = 0;
+			}
+		}
 	}
 
 #include "CPU_emulcycle.h"