Changed Z80 core and fixed raising of interrupt on R register.

8 files changed, 267 insertions, 363 deletions

diff --git a/src/Makefile b/src/Makefile
index 5ff98c5..5103ab6 100644
--- a/src/Makefile
+++ b/src/Makefile
@@ -18,7 +18,7 @@
 # 
 # -------------------------------------------------------------------------
 # 
-# $Id: Makefile,v 1.11 2006-09-16 22:54:59 ianc Exp $
+# $Id: Makefile,v 1.12 2006-09-20 00:02:42 ianc Exp $
 # 
 
 
@@ -212,7 +212,7 @@ memmenu.o: /usr/local/include/SDL11/SDL_mouse.h
 memmenu.o: /usr/local/include/SDL11/SDL_video.h
 memmenu.o: /usr/local/include/SDL11/SDL_mutex.h
 memmenu.o: /usr/local/include/SDL11/SDL_quit.h
-memmenu.o: /usr/local/include/SDL11/SDL_version.h gfx.h gui.h util.h
+memmenu.o: /usr/local/include/SDL11/SDL_version.h gfx.h gui.h expr.h util.h
 util.o: /usr/include/stdio.h /usr/include/sys/cdefs.h
 util.o: /usr/include/sys/_null.h /usr/include/sys/_types.h
 util.o: /usr/include/machine/_types.h /usr/include/string.h
diff --git a/src/memmenu.c b/src/memmenu.c
index 02eeabd..e7909a9 100644
--- a/src/memmenu.c
+++ b/src/memmenu.c
@@ -82,7 +82,8 @@ typedef struct
 
 typedef struct
 {
-    Z80State	s;
+    Z80		s;
+    Z80Val	c;
     MemTrace	hl[TRACEMEM_WIN];
     MemTrace	de[TRACEMEM_WIN];
     MemTrace	sp[TRACEMEM_WIN];
@@ -138,75 +139,75 @@ static int Address(Z80 *z80, const char *p, Z80Word *addr)
 
 static int Expand(void *client, const char *p, long *res)
 {
-    Z80State s;
+    Z80 *cpu;
     int ok=TRUE;
 
-    Z80GetState(client,&s);
+    cpu=client;
 
     if (StrEq(p,"AF"))
-    	*res=s.AF;
+    	*res=cpu->AF.w;
     else if (StrEq(p,"BC"))
-    	*res=s.BC;
+    	*res=cpu->BC.w;
     else if (StrEq(p,"DE"))
-    	*res=s.DE;
+    	*res=cpu->DE.w;
     else if (StrEq(p,"HL"))
-    	*res=s.HL;
+    	*res=cpu->HL.w;
     else if (StrEq(p,"IX"))
-    	*res=s.IX;
+    	*res=cpu->IX.w;
     else if (StrEq(p,"IY"))
-    	*res=s.IY;
+    	*res=cpu->IY.w;
     else if (StrEq(p,"SP"))
-    	*res=s.SP;
+    	*res=cpu->SP;
     else if (StrEq(p,"PC"))
-    	*res=s.PC;
+    	*res=cpu->PC;
     else if (StrEq(p,"A"))
-    	*res=HI(s.AF);
+    	*res=HI(cpu->AF.w);
     else if (StrEq(p,"F"))
-    	*res=LO(s.AF);
+    	*res=LO(cpu->AF.w);
     else if (StrEq(p,"B"))
-    	*res=HI(s.BC);
+    	*res=HI(cpu->BC.w);
     else if (StrEq(p,"C"))
-    	*res=LO(s.BC);
+    	*res=LO(cpu->BC.w);
     else if (StrEq(p,"D"))
-    	*res=HI(s.DE);
+    	*res=HI(cpu->DE.w);
     else if (StrEq(p,"E"))
-    	*res=LO(s.DE);
+    	*res=LO(cpu->DE.w);
     else if (StrEq(p,"H"))
-    	*res=HI(s.HL);
+    	*res=HI(cpu->HL.w);
     else if (StrEq(p,"L"))
-    	*res=LO(s.HL);
+    	*res=LO(cpu->HL.w);
     else if (StrEq(p,"AF_"))
-    	*res=s.AF_;
+    	*res=cpu->AF_;
     else if (StrEq(p,"BC_"))
-    	*res=s.BC_;
+    	*res=cpu->BC_;
     else if (StrEq(p,"DE_"))
-    	*res=s.DE_;
+    	*res=cpu->DE_;
     else if (StrEq(p,"HL_"))
-    	*res=s.HL_;
+    	*res=cpu->HL_;
     else if (StrEq(p,"A_"))
-    	*res=HI(s.AF_);
+    	*res=HI(cpu->AF_);
     else if (StrEq(p,"F_"))
-    	*res=LO(s.AF_);
+    	*res=LO(cpu->AF_);
     else if (StrEq(p,"B_"))
-    	*res=HI(s.BC_);
+    	*res=HI(cpu->BC_);
     else if (StrEq(p,"C_"))
-    	*res=LO(s.BC_);
+    	*res=LO(cpu->BC_);
     else if (StrEq(p,"D_"))
-    	*res=HI(s.DE_);
+    	*res=HI(cpu->DE_);
     else if (StrEq(p,"E_"))
-    	*res=LO(s.DE_);
+    	*res=LO(cpu->DE_);
     else if (StrEq(p,"H_"))
-    	*res=HI(s.HL_);
+    	*res=HI(cpu->HL_);
     else if (StrEq(p,"L_"))
-	*res=LO(s.HL_);
+	*res=LO(cpu->HL_);
     else if (StrEq(p,"IM"))
-	*res=s.IM;
+	*res=cpu->IM;
     else if (StrEq(p,"R"))
-	*res=s.R;
+	*res=cpu->R;
     else if (StrEq(p,"IFF1"))
-	*res=s.IFF1;
+	*res=cpu->IFF1;
     else if (StrEq(p,"IFF2"))
-	*res=s.IFF2;
+	*res=cpu->IFF2;
     else if (p[0]=='@')
     {
 	Z80Word n;
@@ -322,19 +323,19 @@ static const char *FlagString(Z80Byte flag)
 }
 
 
-int DisplayZ80State(Z80State *s, int y, Uint32 col)
+int DisplayZ80State(Z80 *s, Z80Val cycle, int y, Uint32 col)
 {
     GFXPrintPaper(0,y,col,BLACK,
 		  "PC=%4.4x  A=%2.2x     F=%s",
-		  s->PC,s->AF>>8,FlagString(s->AF&0xff));
+		  s->PC,s->AF.w>>8,FlagString(s->AF.w&0xff));
     y+=8;
     GFXPrintPaper(0,y,col,BLACK,
     		  "BC=%4.4x  DE=%4.4x  HL=%4.4x",
-		  s->BC,s->DE,s->HL);
+		  s->BC.w,s->DE.w,s->HL.w);
     y+=8;
     GFXPrintPaper(0,y,col,BLACK,
     		  "IX=%4.4x  IY=%4.4x  SP=%4.4x",
-		  s->IX,s->IY,s->SP);
+		  s->IX.w,s->IY.w,s->SP);
     y+=8;
     GFXPrintPaper(0,y,col,BLACK,
     		  "AF'=%4.4x BC'=%4.4x DE'=%4.4x HL'=%4.4x",
@@ -346,7 +347,7 @@ int DisplayZ80State(Z80State *s, int y, Uint32 col)
     y+=8;
     GFXPrintPaper(0,y,col,BLACK,
     		  "IFF1=%2.2x  IFF2=%2.2x  CY=%8.8lx",
-		  s->IFF1,s->IFF2,s->cycle);
+		  s->IFF1,s->IFF2,cycle);
 
     return y+8;
 }
@@ -387,10 +388,10 @@ static void EnterLong(const char *prompt, long *l)
 }
 
 
-static void DoDisassem(Z80 *z80, const Z80State *s)
+static void DoDisassem(Z80 *z80)
 {
     static int hexmode=FALSE;
-    Z80Word pc=s->PC;
+    Z80Word pc=z80->PC;
     int quit=FALSE;
 
     while(!quit)
@@ -524,7 +525,7 @@ static void DoDisassem(Z80 *z80, const Z80State *s)
 }
 
 
-static void DoDisassemFile(Z80 *z80, const Z80State *s)
+static void DoDisassemFile(Z80 *z80)
 {
     static char fname[FILENAME_MAX]="";
     FILE *fp;
@@ -594,10 +595,11 @@ static int Instruction(Z80 *z80, Z80Val data)
     {
 	Trace t;
 
-	Z80GetState(z80,&t.s);
+	t.s=*z80;
+	t.c=Z80Cycles(z80);
 
-	GetMemTrace(z80,t.hl,t.s.HL-(TRACEMEM_WIN/2+1),TRACEMEM_WIN);
-	GetMemTrace(z80,t.de,t.s.DE-(TRACEMEM_WIN/2+1),TRACEMEM_WIN);
+	GetMemTrace(z80,t.hl,t.s.HL.w-(TRACEMEM_WIN/2+1),TRACEMEM_WIN);
+	GetMemTrace(z80,t.de,t.s.DE.w-(TRACEMEM_WIN/2+1),TRACEMEM_WIN);
 	GetMemTrace(z80,t.sp,t.s.SP-(TRACEMEM_WIN/2+1),TRACEMEM_WIN);
 
 	fwrite(&t,sizeof t,1,trace);
@@ -619,7 +621,7 @@ static int Instruction(Z80 *z80, Z80Val data)
 }
 
 
-static void EnableTrace(Z80 *z80, Z80State *s)
+static void EnableTrace(Z80 *z80)
 {
     if (!trace)
     {
@@ -723,11 +725,11 @@ static void PlaybackTrace(Z80 *z80)
 	if (showmem)
 	{
 	    DisplayTraceMem(0,136,"MEM (SP)",t.sp,t.s.SP);
-	    DisplayTraceMem(100,136,"MEM (HL)",t.hl,t.s.HL);
-	    DisplayTraceMem(200,136,"MEM (DE)",t.de,t.s.DE);
+	    DisplayTraceMem(100,136,"MEM (HL)",t.hl,t.s.HL.w);
+	    DisplayTraceMem(200,136,"MEM (DE)",t.de,t.s.DE.w);
 	}
 	else
-	    DisplayZ80State(&t.s,136,WHITE);
+	    DisplayZ80State(&t.s,t.c,136,WHITE);
 
 	for(f=0;f<10;f++)
 	{
@@ -971,10 +973,10 @@ static void DoMonitor(Z80 *z80)
 
     while(!quit)
     {
+	Z80Word pc;
 	MemTrace mt[TRACEMEM_WIN];
 	const char *brk;
 	SDL_Event *e;
-	Z80State s;
 	int f;
 
 	step=FALSE;
@@ -984,25 +986,25 @@ static void DoMonitor(Z80 *z80)
     	CentrePaper("MONITOR",0,WHITE,BLACK);
     	CentrePaper("Press F1 for help",9,RED,BLACK);
 
-	Z80GetState(z80,&s);
-
 	if (showmem)
 	{
-	    GetMemTrace(z80,mt,s.SP-(TRACEMEM_WIN/2+1),TRACEMEM_WIN);
-	    DisplayTraceMem(0,136,"MEM (SP)",mt,s.SP);
-	    GetMemTrace(z80,mt,s.HL-(TRACEMEM_WIN/2+1),TRACEMEM_WIN);
-	    DisplayTraceMem(100,136,"MEM (HL)",mt,s.HL);
-	    GetMemTrace(z80,mt,s.DE-(TRACEMEM_WIN/2+1),TRACEMEM_WIN);
-	    DisplayTraceMem(200,136,"MEM (DE)",mt,s.DE);
+	    GetMemTrace(z80,mt,z80->SP-(TRACEMEM_WIN/2+1),TRACEMEM_WIN);
+	    DisplayTraceMem(0,136,"MEM (SP)",mt,z80->SP);
+	    GetMemTrace(z80,mt,z80->HL.w-(TRACEMEM_WIN/2+1),TRACEMEM_WIN);
+	    DisplayTraceMem(100,136,"MEM (HL)",mt,z80->HL.w);
+	    GetMemTrace(z80,mt,z80->DE.w-(TRACEMEM_WIN/2+1),TRACEMEM_WIN);
+	    DisplayTraceMem(200,136,"MEM (DE)",mt,z80->DE.w);
 	}
 	else
 	{
 	    int y;
 
-	    y=DisplayZ80State(&s,136,WHITE);
+	    y=DisplayZ80State(z80,Z80Cycles(z80),136,WHITE);
 	    GFXPrint(0,y,GREEN,"%s",ZX81Info(z80));
 	}
 
+	pc=z80->PC;
+
 	for(f=0;f<10;f++)
 	{
 	    char str[80];
@@ -1017,9 +1019,9 @@ static void DoMonitor(Z80 *z80)
 	    else
 		paper=BLACK;
 
-	    GFXPrintPaper(0,y,GREEN,paper,"%4.4x ",s.PC);
+	    GFXPrintPaper(0,y,GREEN,paper,"%4.4x ",pc);
 
-	    strcpy(str,Z80Disassemble(z80,&s.PC));
+	    strcpy(str,Z80Disassemble(z80,&pc));
 	    p=strtok(str,";");
 	    GFXPrintPaper(40,y,WHITE,paper,"%s",str);
 	}
@@ -1117,11 +1119,8 @@ int MemoryMenu(Z80 *z80)
     SDL_Event *e;
     int done=FALSE;
     int quit=FALSE;
-    Z80State s;
     int y;
 
-    Z80GetState(z80,&s);
-
     GFXKeyRepeat(TRUE);
 
     while(!done)
@@ -1134,16 +1133,16 @@ int MemoryMenu(Z80 *z80)
 	switch(e->key.keysym.sym)
 	{
 	    case SDLK_1:
-	    	DoDisassem(z80,&s);
+	    	DoDisassem(z80);
 		break;
 
 	    case SDLK_2:
-	    	DoDisassemFile(z80,&s);
+	    	DoDisassemFile(z80);
 	    	break;
 
 	    case SDLK_3:
 		if (!trace)
-		    EnableTrace(z80,&s);
+		    EnableTrace(z80);
 		else
 		    DisableTrace(z80);
 	    	break;
@@ -1190,7 +1189,7 @@ int MemoryMenu(Z80 *z80)
 		GFXClear(BLACK);
 		Centre("CURRENT STATE",0,WHITE);
 		Centre("Press a key",9,RED);
-		y=DisplayZ80State(&s,20,WHITE);
+		y=DisplayZ80State(z80,Z80Cycles(z80),20,WHITE);
 		GFXPrint(0,y,GREEN,"%s",ZX81Info(z80));
 		GFXEndFrame(FALSE);
 		GFXWaitKey();
@@ -1214,11 +1213,9 @@ int MemoryMenu(Z80 *z80)
 
 void DisplayState(Z80 *z80)
 {
-    Z80State s;
     int y;
 
-    Z80GetState(z80,&s);
-    y=DisplayZ80State(&s,GFX_HEIGHT/2,RED);
+    y=DisplayZ80State(z80,Z80Cycles(z80),GFX_HEIGHT/2,RED);
     GFXPrintPaper(0,y,GREEN,BLACK,"%s",ZX81Info(z80));
 }
 
diff --git a/src/z80.c b/src/z80.c
index 3a15a22..be50494 100644
--- a/src/z80.c
+++ b/src/z80.c
@@ -55,28 +55,28 @@ static void Z80_CheckInterrupt(Z80 *cpu)
 {
     /* Check interrupts
     */
-    if (cpu->raise)
+    if (PRIV->raise)
     {
-    	if (cpu->nmi)
+    	if (PRIV->nmi)
 	{
-	    if (cpu->halt)
+	    if (PRIV->halt)
 	    {
-		cpu->halt=FALSE;
+		PRIV->halt=FALSE;
 		CALLBACK(eZ80_Halt,0);
 		cpu->PC++;
 	    }
 
 	    TSTATE(2);
 	    cpu->IFF1=0;
-	    cpu->nmi=FALSE;
+	    PRIV->nmi=FALSE;
 	    PUSH(cpu->PC);
 	    cpu->PC=0x66;
 	}
     	else if (cpu->IFF1)
 	{
-	    if (cpu->halt)
+	    if (PRIV->halt)
 	    {
-		cpu->halt=FALSE;
+		PRIV->halt=FALSE;
 		CALLBACK(eZ80_Halt,0);
 		cpu->PC++;
 	    }
@@ -88,7 +88,7 @@ static void Z80_CheckInterrupt(Z80 *cpu)
 		default:
 		case 0:
 		    INC_R;
-		    Z80_Decode(cpu,cpu->devbyte);
+		    Z80_Decode(cpu,PRIV->devbyte);
 		    return;
 		    break;
 
@@ -99,12 +99,12 @@ static void Z80_CheckInterrupt(Z80 *cpu)
 
 		case 2:
 		    PUSH(cpu->PC);
-		    cpu->PC=(Z80Word)cpu->I*256+cpu->devbyte;
+		    cpu->PC=(Z80Word)cpu->I*256+PRIV->devbyte;
 		    break;
 	    }
 	}
 
-	cpu->raise=FALSE;
+	PRIV->raise=FALSE;
     }
 }
 
@@ -138,19 +138,29 @@ Z80     *Z80Init(Z80ReadMemory read_memory,
 
     if (cpu)
     {
+    	cpu->priv=malloc(sizeof *cpu->priv);
+
+	if (cpu->priv)
+	{
 #ifndef ENABLE_ARRAY_MEMORY
-	cpu->mread=read_memory;
-	cpu->mwrite=write_memory;
-	cpu->disread=read_for_disassem;
+	    PRIV->mread=read_memory;
+	    PRIV->mwrite=write_memory;
+	    PRIV->disread=read_for_disassem;
 #endif
-	cpu->pread=read_port;
-	cpu->pwrite=write_port;
+	    PRIV->pread=read_port;
+	    PRIV->pwrite=write_port;
 
-	for(f=0;f<eZ80_NO_CALLBACK;f++)
-	    for(r=0;r<MAX_PER_CALLBACK;r++)
-		cpu->callback[f][r]=NULL;
+	    for(f=0;f<eZ80_NO_CALLBACK;f++)
+		for(r=0;r<MAX_PER_CALLBACK;r++)
+		    PRIV->callback[f][r]=NULL;
 
-	Z80Reset(cpu);
+	    Z80Reset(cpu);
+	}
+	else
+	{
+	    free(cpu);
+	    cpu=NULL;
+	}
     }
 
     return cpu;
@@ -159,7 +169,7 @@ Z80     *Z80Init(Z80ReadMemory read_memory,
 
 void Z80Reset(Z80 *cpu)
 {
-    cpu->cycle=0;
+    PRIV->cycle=0;
     cpu->PC=0;
 
     cpu->AF.w=0xffff;
@@ -180,28 +190,22 @@ void Z80Reset(Z80 *cpu)
     cpu->IM=0;
     cpu->I=0;
     cpu->R=0;
-    cpu->halt=0;
+    PRIV->halt=0;
 
-    cpu->raise=FALSE;
-    cpu->nmi=FALSE;
+    PRIV->raise=FALSE;
+    PRIV->nmi=FALSE;
 }
 
 
-void Z80SetPC(Z80 *cpu,Z80Word PC)
-{
-    cpu->PC=PC;
-}
-
-
-Z80Word Z80GetPC(Z80 *cpu)
+Z80Val Z80Cycles(Z80 *cpu)
 {
-    return cpu->PC;
+    return PRIV->cycle;
 }
 
 
 void Z80ResetCycles(Z80 *cpu, Z80Val cycles)
 {
-    cpu->cycle=cycles;
+    PRIV->cycle=cycles;
 }
 
 
@@ -211,9 +215,9 @@ int Z80LodgeCallback(Z80 *cpu, Z80CallbackReason reason, Z80Callback callback)
 
     for(f=0;f<MAX_PER_CALLBACK;f++)
     {
-    	if (!cpu->callback[reason][f])
+    	if (!PRIV->callback[reason][f])
 	{
-	    cpu->callback[reason][f]=callback;
+	    PRIV->callback[reason][f]=callback;
 	    return TRUE;
 	}
     }
@@ -227,23 +231,27 @@ void Z80RemoveCallback(Z80 *cpu, Z80CallbackReason reason, Z80Callback callback)
     int f;
 
     for(f=0;f<MAX_PER_CALLBACK;f++)
-    	if (cpu->callback[reason][f]==callback)
-	    cpu->callback[reason][f]=NULL;
+    {
+    	if (PRIV->callback[reason][f]==callback)
+	{
+	    PRIV->callback[reason][f]=NULL;
+	}
+    }
 }
 
 
 void Z80Interrupt(Z80 *cpu, Z80Byte devbyte)
 {
-    cpu->raise=TRUE;
-    cpu->devbyte=devbyte;
-    cpu->nmi=FALSE;
+    PRIV->raise=TRUE;
+    PRIV->devbyte=devbyte;
+    PRIV->nmi=FALSE;
 }
 
 
 void Z80NMI(Z80 *cpu)
 {
-    cpu->raise=TRUE;
-    cpu->nmi=TRUE;
+    PRIV->raise=TRUE;
+    PRIV->nmi=TRUE;
 }
 
 
@@ -251,12 +259,12 @@ int Z80SingleStep(Z80 *cpu)
 {
     Z80Byte opcode;
 
-    cpu->last_cb=TRUE;
-    cpu->shift=0;
+    PRIV->last_cb=TRUE;
+    PRIV->shift=0;
 
     Z80_CheckInterrupt(cpu);
 
-    CALLBACK(eZ80_Instruction,cpu->cycle);
+    CALLBACK(eZ80_Instruction,PRIV->cycle);
 
     INC_R;
 
@@ -264,7 +272,7 @@ int Z80SingleStep(Z80 *cpu)
 
     Z80_Decode(cpu,opcode);
 
-    return cpu->last_cb;
+    return PRIV->last_cb;
 }
 
 
@@ -274,68 +282,6 @@ void Z80Exec(Z80 *cpu)
 }
 
 
-void Z80GetState(Z80 *cpu, Z80State *state)
-{
-    state->cycle=	cpu->cycle;
-
-    state->AF	=	cpu->AF.w;
-    state->BC	=	cpu->BC.w;
-    state->DE	=	cpu->DE.w;
-    state->HL	=	cpu->HL.w;
-
-    state->AF_	=	cpu->AF_;
-    state->BC_	=	cpu->BC_;
-    state->DE_	=	cpu->DE_;
-    state->HL_	=	cpu->HL_;
-
-    state->IX	=	cpu->IX.w;
-    state->IY	=	cpu->IY.w;
-
-    state->SP	=	cpu->SP;
-    state->PC	=	cpu->PC;
-
-    state->IFF1	=	cpu->IFF1;
-    state->IFF2	=	cpu->IFF2;
-    state->IM	=	cpu->IM;
-    state->I	=	cpu->I;
-    state->R	=	cpu->R;
-}
-
-
-void Z80SetState(Z80 *cpu, const Z80State *state)
-{
-    cpu->cycle	=	state->cycle;
-
-    cpu->AF.w	=	state->AF;
-    cpu->BC.w	=	state->BC;
-    cpu->DE.w	=	state->DE;
-    cpu->HL.w	=	state->HL;
-
-    cpu->AF_	=	state->AF_;
-    cpu->BC_	=	state->BC_;
-    cpu->DE_	=	state->DE_;
-    cpu->HL_	=	state->HL_;
-
-    cpu->IX.w	=	state->IX;
-    cpu->IY.w	=	state->IY;
-
-    cpu->SP	=	state->SP;
-    cpu->PC	=	state->PC;
-
-    cpu->IFF1	=	state->IFF1;
-    cpu->IFF2	=	state->IFF2;
-    cpu->IM	=	state->IM;
-    cpu->I	=	state->I;
-    cpu->R	=	state->R;
-}
-
-
-Z80Val Z80Cycles(Z80 *cpu)
-{
-    return cpu->cycle;
-}
-
-
 void Z80SetLabels(Z80Label labels[])
 {
     z80_labels=labels;
@@ -364,7 +310,7 @@ const char *Z80Disassemble(Z80 *cpu, Z80Word *pc)
 #ifdef ENABLE_ARRAY_MEMORY
 	strcat(s,Z80_Dis_Printf(" %.2x",(int)Z80_MEMORY[opc++]));
 #else
-	strcat(s,Z80_Dis_Printf(" %.2x",(int)cpu->disread(cpu,opc++)));
+	strcat(s,Z80_Dis_Printf(" %.2x",(int)PRIV->disread(cpu,opc++)));
 #endif
     }
 
diff --git a/src/z80.h b/src/z80.h
index f6bc041..000b950 100644
--- a/src/z80.h
+++ b/src/z80.h
@@ -35,12 +35,6 @@
 /* ---------------------------------------- TYPES
 */
 
-/* The processor
-*/
-struct Z80;
-typedef struct Z80 Z80;
-
-
 /* Large unsigned type
 */
 typedef unsigned long Z80Val;
@@ -61,6 +55,53 @@ typedef signed char Z80Relative;
 typedef unsigned short Z80Word;
 
 
+/* A Z80 16-bit register.  To access the HI/LO component use the indexes
+   Z80_HI_WORD and Z80_LO_WORD which will be initialised once Z80Init has been
+   called.
+*/
+typedef union
+{
+    Z80Word		w;
+    Z80Byte		b[2];
+} Z80Reg;
+
+extern int Z80_HI_WORD;
+extern int Z80_LO_WORD;
+
+
+/* The processor
+*/
+struct Z80Private;
+
+typedef struct
+{
+    Z80Word		PC;
+
+    Z80Reg		AF;
+    Z80Reg		BC;
+    Z80Reg		DE;
+    Z80Reg		HL;
+
+    Z80Word		AF_;
+    Z80Word		BC_;
+    Z80Word		DE_;
+    Z80Word		HL_;
+
+    Z80Reg		IX;
+    Z80Reg		IY;
+
+    Z80Word		SP;
+
+    Z80Byte		IFF1;
+    Z80Byte		IFF2;
+    Z80Byte		IM;
+    Z80Byte		I;
+    Z80Byte		R;
+
+    struct Z80Private	*priv;
+} Z80;
+
+
 /* Interfaces used to handle memory
 */
 typedef	Z80Byte	(*Z80ReadMemory)(Z80 *cpu, Z80Word address);
@@ -100,36 +141,6 @@ typedef enum
 } Z80CallbackReason;
 
 
-/* Get/settable state of the Z80
-*/
-typedef struct
-{
-    Z80Word	PC;
-    Z80Word	SP;
-
-    Z80Val	cycle;
-
-    Z80Word	AF;
-    Z80Word	BC;
-    Z80Word	DE;
-    Z80Word	HL;
-
-    Z80Word	AF_;	/* Alternate registers */
-    Z80Word	BC_;
-    Z80Word	DE_;
-    Z80Word	HL_;
-
-    Z80Word	IX;
-    Z80Word	IY;
-
-    Z80Byte	IFF1;
-    Z80Byte	IFF2;
-    Z80Byte	IM;
-    Z80Byte	I;
-    Z80Byte	R;
-} Z80State;
-
-
 /* Flags in the F register
 */
 typedef enum
@@ -179,21 +190,6 @@ Z80	*Z80Init(Z80ReadMemory read_memory,
 void	Z80Reset(Z80 *cpu);
 
 
-/* Sets the PC
-*/
-void	Z80SetPC(Z80 *cpu, Z80Word PC);
-
-
-/* Gets the PC
-*/
-Z80Word	Z80GetPC(Z80 *cpu);
-
-
-/* Sets the cycle count to the specified count
-*/
-void	Z80ResetCycles(Z80 *cpu, Z80Val cycles);
-
-
 /* Lodge a callback to be invoked after special events.  Returns FALSE
    if the callback couldn't be lodged (there is a max of 10 callbacks per
    reason).
@@ -233,11 +229,10 @@ int	Z80SingleStep(Z80 *cpu);
 void	Z80Exec(Z80 *cpu);
 
 
-/* Interrogate the state of the Z80
+/* Manipulate the cylce count of the Z80
 */
 Z80Val	Z80Cycles(Z80 *cpu);
-void	Z80GetState(Z80 *cpu, Z80State *state);
-void	Z80SetState(Z80 *cpu, const Z80State *state);
+void	Z80ResetCycles(Z80 *cpu, Z80Val cycles);
 
 
 /* Set address to label mappings for the disassembler
diff --git a/src/z80_decode.c b/src/z80_decode.c
index c134b7b..a8f66ca 100644
--- a/src/z80_decode.c
+++ b/src/z80_decode.c
@@ -40,8 +40,11 @@ static Z80Byte		Stable[512];
 static Z80Byte		Ztable[512];
 
 
-static int HI;
-static int LO;
+int Z80_HI_WORD;
+int Z80_LO_WORD;
+
+#define HI Z80_HI_WORD
+#define LO Z80_LO_WORD
 
 /* ---------------------------------------- MISC FUNCTIONS
 */
@@ -127,8 +130,8 @@ static Z80Word FPEEKW(Z80 *cpu, Z80Word addr)
 
 static void FPOKEW(Z80 *cpu, Z80Word addr, Z80Word val)
 {
-    cpu->mwrite(cpu,addr,val);
-    cpu->mwrite(cpu,addr+1,val>>8);
+    PRIV->mwrite(cpu,addr,val);
+    PRIV->mwrite(cpu,addr+1,val>>8);
 }
 #endif
 
@@ -1020,9 +1023,9 @@ static void DecodeED(Z80 *cpu, Z80Byte opcode)
 	case 0x40:	/* IN B,(C) */
 	    TSTATE(12);
 
-	    if (cpu->pread)
+	    if (PRIV->pread)
 	    {
-		cpu->BC.b[HI]=cpu->pread(cpu,cpu->BC.w);
+		cpu->BC.b[HI]=PRIV->pread(cpu,cpu->BC.w);
 	    }
 	    else
 	    {
@@ -1035,7 +1038,7 @@ static void DecodeED(Z80 *cpu, Z80Byte opcode)
 
 	case 0x41:	/* OUT (C),B */
 	    TSTATE(12);
-	    if (cpu->pwrite) cpu->pwrite(cpu,cpu->BC.w,cpu->BC.b[HI]);
+	    if (PRIV->pwrite) PRIV->pwrite(cpu,cpu->BC.w,cpu->BC.b[HI]);
 	    break;
 
 	case 0x42:	/* SBC HL,BC */
@@ -1079,9 +1082,9 @@ static void DecodeED(Z80 *cpu, Z80Byte opcode)
 	case 0x48:	/* IN C,(C) */
 	    TSTATE(12);
 
-	    if (cpu->pread)
+	    if (PRIV->pread)
 	    {
-		cpu->BC.b[LO]=cpu->pread(cpu,cpu->BC.w);
+		cpu->BC.b[LO]=PRIV->pread(cpu,cpu->BC.w);
 	    }
 	    else
 	    {
@@ -1094,7 +1097,7 @@ static void DecodeED(Z80 *cpu, Z80Byte opcode)
 
 	case 0x49:	/* OUT (C),C */
 	    TSTATE(12);
-	    if (cpu->pwrite) cpu->pwrite(cpu,cpu->BC.w,cpu->BC.b[LO]);
+	    if (PRIV->pwrite) PRIV->pwrite(cpu,cpu->BC.w,cpu->BC.b[LO]);
 	    break;
 
 	case 0x4a:	/* ADC HL,BC */
@@ -1139,9 +1142,9 @@ static void DecodeED(Z80 *cpu, Z80Byte opcode)
 	case 0x50:	/* IN D,(C) */
 	    TSTATE(12);
 
-	    if (cpu->pread)
+	    if (PRIV->pread)
 	    {
-		cpu->DE.b[HI]=cpu->pread(cpu,cpu->BC.w);
+		cpu->DE.b[HI]=PRIV->pread(cpu,cpu->BC.w);
 	    }
 	    else
 	    {
@@ -1154,7 +1157,7 @@ static void DecodeED(Z80 *cpu, Z80Byte opcode)
 
 	case 0x51:	/* OUT (C),D */
 	    TSTATE(12);
-	    if (cpu->pwrite) cpu->pwrite(cpu,cpu->BC.w,cpu->DE.b[HI]);
+	    if (PRIV->pwrite) PRIV->pwrite(cpu,cpu->BC.w,cpu->DE.b[HI]);
 	    break;
 
 	case 0x52:	/* SBC HL,DE */
@@ -1198,9 +1201,9 @@ static void DecodeED(Z80 *cpu, Z80Byte opcode)
 	case 0x58:	/* IN E,(C) */
 	    TSTATE(12);
 
-	    if (cpu->pread)
+	    if (PRIV->pread)
 	    {
-		cpu->DE.b[LO]=cpu->pread(cpu,cpu->BC.w);
+		cpu->DE.b[LO]=PRIV->pread(cpu,cpu->BC.w);
 	    }
 	    else
 	    {
@@ -1213,7 +1216,7 @@ static void DecodeED(Z80 *cpu, Z80Byte opcode)
 
 	case 0x59:	/* OUT (C),E */
 	    TSTATE(12);
-	    if (cpu->pwrite) cpu->pwrite(cpu,cpu->BC.w,cpu->DE.b[LO]);
+	    if (PRIV->pwrite) PRIV->pwrite(cpu,cpu->BC.w,cpu->DE.b[LO]);
 	    break;
 
 	case 0x5a:	/* ADC HL,DE */
@@ -1257,9 +1260,9 @@ static void DecodeED(Z80 *cpu, Z80Byte opcode)
 	case 0x60:	/* IN H,(C) */
 	    TSTATE(12);
 
-	    if (cpu->pread)
+	    if (PRIV->pread)
 	    {
-		cpu->HL.b[HI]=cpu->pread(cpu,cpu->BC.w);
+		cpu->HL.b[HI]=PRIV->pread(cpu,cpu->BC.w);
 	    }
 	    else
 	    {
@@ -1272,7 +1275,7 @@ static void DecodeED(Z80 *cpu, Z80Byte opcode)
 
 	case 0x61:	/* OUT (C),H */
 	    TSTATE(12);
-	    if (cpu->pwrite) cpu->pwrite(cpu,cpu->BC.w,cpu->HL.b[HI]);
+	    if (PRIV->pwrite) PRIV->pwrite(cpu,cpu->BC.w,cpu->HL.b[HI]);
 	    break;
 
 	case 0x62:	/* SBC HL,HL */
@@ -1327,9 +1330,9 @@ static void DecodeED(Z80 *cpu, Z80Byte opcode)
 	case 0x68:	/* IN L,(C) */
 	    TSTATE(12);
 
-	    if (cpu->pread)
+	    if (PRIV->pread)
 	    {
-		cpu->HL.b[LO]=cpu->pread(cpu,cpu->BC.w);
+		cpu->HL.b[LO]=PRIV->pread(cpu,cpu->BC.w);
 	    }
 	    else
 	    {
@@ -1342,7 +1345,7 @@ static void DecodeED(Z80 *cpu, Z80Byte opcode)
 
 	case 0x69:	/* OUT (C),L */
 	    TSTATE(12);
-	    if (cpu->pwrite) cpu->pwrite(cpu,cpu->BC.w,cpu->HL.b[LO]);
+	    if (PRIV->pwrite) PRIV->pwrite(cpu,cpu->BC.w,cpu->HL.b[LO]);
 	    break;
 
 	case 0x6a:	/* ADC HL,HL */
@@ -1400,9 +1403,9 @@ static void DecodeED(Z80 *cpu, Z80Byte opcode)
 
 	    TSTATE(12);
 
-	    if (cpu->pread)
+	    if (PRIV->pread)
 	    {
-		b=cpu->pread(cpu,cpu->BC.w);
+		b=PRIV->pread(cpu,cpu->BC.w);
 	    }
 	    else
 	    {
@@ -1416,7 +1419,7 @@ static void DecodeED(Z80 *cpu, Z80Byte opcode)
 
 	case 0x71:	/* OUT (C) */
 	    TSTATE(12);
-	    if (cpu->pwrite) cpu->pwrite(cpu,cpu->BC.w,0);
+	    if (PRIV->pwrite) PRIV->pwrite(cpu,cpu->BC.w,0);
 	    break;
 
 	case 0x72:	/* SBC HL,SP */
@@ -1460,9 +1463,9 @@ static void DecodeED(Z80 *cpu, Z80Byte opcode)
 	case 0x78:	/* IN A,(C) */
 	    TSTATE(12);
 
-	    if (cpu->pread)
+	    if (PRIV->pread)
 	    {
-		cpu->AF.b[HI]=cpu->pread(cpu,cpu->BC.w);
+		cpu->AF.b[HI]=PRIV->pread(cpu,cpu->BC.w);
 	    }
 	    else
 	    {
@@ -1475,7 +1478,7 @@ static void DecodeED(Z80 *cpu, Z80Byte opcode)
 
 	case 0x79:	/* OUT (C),A */
 	    TSTATE(12);
-	    if (cpu->pwrite) cpu->pwrite(cpu,cpu->BC.w,cpu->AF.b[HI]);
+	    if (PRIV->pwrite) PRIV->pwrite(cpu,cpu->BC.w,cpu->AF.b[HI]);
 	    break;
 
 	case 0x7a:	/* ADC HL,SP */
@@ -1697,7 +1700,7 @@ static void ShiftedDecodeCB(Z80 *cpu, Z80Byte opcode, Z80Relative offset)
 
     /* See if we've come here from a IX/IY shift.
     */
-    switch (cpu->shift)
+    switch (PRIV->shift)
     {
     	case 0xdd:
 	    addr=cpu->IX.w+offset;
@@ -1762,7 +1765,7 @@ void Z80_Decode(Z80 *cpu, Z80Byte opcode)
 
     /* See if we've come here from a IX/IY shift
     */
-    switch (cpu->shift)
+    switch (PRIV->shift)
     {
     	case 0xdd:
 	    HL=&(cpu->IX.w);
@@ -2168,10 +2171,10 @@ void Z80_Decode(Z80 *cpu, Z80Byte opcode)
 	    TSTATE(4);
 	    cpu->PC--;
 
-	    if (!cpu->halt)
+	    if (!PRIV->halt)
 		CALLBACK(eZ80_Halt,1);
 
-	    cpu->halt=TRUE;
+	    PRIV->halt=TRUE;
 	    break;
 
 	case 0x77:	/* LD (HL),A */
@@ -2244,7 +2247,7 @@ void Z80_Decode(Z80 *cpu, Z80Byte opcode)
 
 	    /* Check for previous IX/IY shift.
 	    */
-	    if (cpu->shift!=0)
+	    if (PRIV->shift!=0)
 	    {
 		Z80Relative cb_offset;
 
@@ -2289,13 +2292,13 @@ void Z80_Decode(Z80 *cpu, Z80Byte opcode)
 
 	case 0xd3:	/* OUT (n),A */
 	    TSTATE(11);
-	    if (cpu->pwrite)
+	    if (PRIV->pwrite)
 	    {
 		Z80Word port;
 
 		port=FETCH_BYTE;
 		port|=(Z80Word)cpu->AF.b[HI]<<8;
-	    	cpu->pwrite(cpu,port,cpu->AF.b[HI]);
+	    	PRIV->pwrite(cpu,port,cpu->AF.b[HI]);
 	    }
 	    else
 	    	cpu->PC++;
@@ -2336,13 +2339,13 @@ void Z80_Decode(Z80 *cpu, Z80Byte opcode)
 
 	case 0xdb:	/* IN A,(n) */
 	    TSTATE(11);
-	    if (cpu->pread)
+	    if (PRIV->pread)
 	    {
 		Z80Word port;
 
 		port=FETCH_BYTE;
 		port|=(Z80Word)cpu->AF.b[HI]<<8;
-		cpu->AF.b[HI]=cpu->pread(cpu,port);
+		cpu->AF.b[HI]=PRIV->pread(cpu,port);
 	    }
 	    else
 	    	cpu->PC++;
@@ -2356,7 +2359,7 @@ void Z80_Decode(Z80 *cpu, Z80Byte opcode)
 	    TSTATE(4);
 	    INC_R;
 
-	    cpu->shift=opcode;
+	    PRIV->shift=opcode;
 	    Z80_Decode(cpu,FETCH_BYTE);
 	    break;
 
@@ -2510,7 +2513,7 @@ void Z80_Decode(Z80 *cpu, Z80Byte opcode)
 	    TSTATE(4);
 	    INC_R;
 
-	    cpu->shift=opcode;
+	    PRIV->shift=opcode;
 	    Z80_Decode(cpu,FETCH_BYTE);
 	    break;
 
diff --git a/src/z80_dis.c b/src/z80_dis.c
index 6204f0d..8a8ade8 100644
--- a/src/z80_dis.c
+++ b/src/z80_dis.c
@@ -67,7 +67,7 @@ Z80Byte Z80_Dis_FetchByte(Z80 *cpu, Z80Word *pc)
 #ifdef ENABLE_ARRAY_MEMORY
     return Z80_MEMORY[(*pc)++];
 #else
-    return cpu->disread(cpu,(*pc)++);
+    return cpu->priv->disread(cpu,(*pc)++);
 #endif
 }
 
@@ -1463,7 +1463,7 @@ static void DIS_DJNZ (Z80 *z80, Z80Byte op, Z80Word *pc)
 #ifdef ENABLE_ARRAY_MEMORY
     new=*pc+(Z80Relative)Z80_MEMORY[*pc]+1;
 #else
-    new=*pc+(Z80Relative)z80->disread(z80,*pc)+1;
+    new=*pc+(Z80Relative)z80->priv->disread(z80,*pc)+1;
 #endif
     (*pc)++;
     Z80_Dis_Set("djnz",Z80_Dis_Printf("$%.4x",new));
@@ -1482,7 +1482,7 @@ static void DIS_JR (Z80 *z80, Z80Byte op, Z80Word *pc)
 #ifdef ENABLE_ARRAY_MEMORY
     new=*pc+(Z80Relative)Z80_MEMORY[*pc]+1;
 #else
-    new=*pc+(Z80Relative)z80->disread(z80,*pc)+1;
+    new=*pc+(Z80Relative)z80->priv->disread(z80,*pc)+1;
 #endif
     (*pc)++;
 
@@ -1507,7 +1507,7 @@ static void DIS_JR_CO (Z80 *z80, Z80Byte op, Z80Word *pc)
 #ifdef ENABLE_ARRAY_MEMORY
     new=*pc+(Z80Relative)Z80_MEMORY[*pc]+1;
 #else
-    new=*pc+(Z80Relative)z80->disread(z80,*pc)+1;
+    new=*pc+(Z80Relative)z80->priv->disread(z80,*pc)+1;
 #endif
     (*pc)++;
 
diff --git a/src/z80_private.h b/src/z80_private.h
index d031497..be45e56 100644
--- a/src/z80_private.h
+++ b/src/z80_private.h
@@ -45,40 +45,10 @@
 /* ---------------------------------------- TYPES
 */
 
-typedef signed short	sword;
-
-typedef union
-{
-    Z80Word		w;
-    Z80Byte		b[2];
-} Z80Reg;
-
-struct Z80
+struct Z80Private
 {
     Z80Val		cycle;
 
-    Z80Word		PC;
-
-    Z80Reg		AF;
-    Z80Reg		BC;
-    Z80Reg		DE;
-    Z80Reg		HL;
-
-    Z80Word		AF_;
-    Z80Word		BC_;
-    Z80Word		DE_;
-    Z80Word		HL_;
-
-    Z80Reg		IX;
-    Z80Reg		IY;
-
-    Z80Word		SP;
-
-    Z80Byte		IFF1;
-    Z80Byte		IFF2;
-    Z80Byte		IM;
-    Z80Byte		I;
-    Z80Byte		R;
     int			halt;
 
     Z80Byte		shift;
@@ -102,6 +72,8 @@ struct Z80
     int			last_cb;
 };
 
+#define PRIV		cpu->priv
+
 
 /* ---------------------------------------- ARRAY MEMORY
 */
@@ -126,9 +98,9 @@ extern Z80Byte	Z80_MEMORY[];
 			int f;					\
 								\
 			for(f=0;f<MAX_PER_CALLBACK;f++)		\
-			    if (cpu->callback[r][f])		\
-				cpu->last_cb &=			\
-				    cpu->callback[r][f](cpu,d);	\
+			    if (PRIV->callback[r][f])		\
+				PRIV->last_cb &=		\
+				    PRIV->callback[r][f](cpu,d);\
 			} while(0)
 
 /* Flag register
@@ -183,13 +155,13 @@ static inline Z80Word PEEKW(Z80Word addr)
 
 #else
 
-#define PEEK(addr)		(cpu->mread(cpu,addr))
+#define PEEK(addr)		(PRIV->mread(cpu,addr))
 #define PEEKW(addr)		FPEEKW(cpu,addr)
 
-#define POKE(addr,val)		cpu->mwrite(cpu,addr,val)
+#define POKE(addr,val)		PRIV->mwrite(cpu,addr,val)
 #define POKEW(addr,val)		FPOKEW(cpu,addr,val)
 
-#define FETCH_BYTE		(cpu->mread(cpu,cpu->PC++))
+#define FETCH_BYTE		(PRIV->mread(cpu,cpu->PC++))
 #define FETCH_WORD		(cpu->PC+=2,FPEEKW(cpu,cpu->PC-2))
 
 #endif
@@ -204,10 +176,10 @@ static inline Z80Word PEEKW(Z80Word addr)
 
 #define CARRY			IS_C
 
-#define IS_IX_IY		(cpu->shift==0xdd || cpu->shift==0xfd)
+#define IS_IX_IY		(PRIV->shift==0xdd || PRIV->shift==0xfd)
 #define OFFSET(off)		off=(IS_IX_IY ? (Z80Relative)FETCH_BYTE:0)
 
-#define TSTATE(n)		cpu->cycle+=n
+#define TSTATE(n)		PRIV->cycle+=n
 
 #define ADD_R(v)		cpu->R=((cpu->R&0x80)|((cpu->R+(v))&0x7f))
 #define INC_R			ADD_R(1)
@@ -228,8 +200,8 @@ static inline Z80Word PEEKW(Z80Word addr)
 				{					\
 				    Z80Word pushv=REG;			\
 				    cpu->SP-=2;				\
-				    cpu->mwrite(cpu,cpu->SP,pushv);	\
-				    cpu->mwrite(cpu,cpu->SP+1,pushv>>8);\
+				    PRIV->mwrite(cpu,cpu->SP,pushv);	\
+				    PRIV->mwrite(cpu,cpu->SP+1,pushv>>8);\
 				} while(0)
 #endif
 
@@ -257,11 +229,11 @@ static inline Z80Word PEEKW(Z80Word addr)
 
 #define OUT(P,V)		do				\
 				{				\
-				    if (cpu->pwrite)		\
-				    	cpu->pwrite(cpu,P,V);	\
+				    if (PRIV->pwrite)		\
+				    	PRIV->pwrite(cpu,P,V);	\
 				} while(0)
 
-#define IN(P)			(cpu->pread?cpu->pread(cpu,P):0)
+#define IN(P)			(PRIV->pread?PRIV->pread(cpu,P):0)
 
 
 
diff --git a/src/zx81.c b/src/zx81.c
index efaef52..35a6558 100644
--- a/src/zx81.c
+++ b/src/zx81.c
@@ -52,7 +52,7 @@ static const int	ROMLEN=0x2000;
 static const int	ROM_SAVE=0x2fc;
 static const int	ROM_LOAD=0x347;
 
-static const Z80Val	HSYNC_PERIOD=208;
+static const Z80Val	NMI_PERIOD=208;
 
 /* The ZX81 screen
 */
@@ -239,9 +239,9 @@ static const char *ConvertFilename(Z80Word addr)
 }
 
 
-static void LoadTape(Z80State *state)
+static void LoadTape(Z80 *cpu)
 {
-    const char *p=ConvertFilename(state->DE);
+    const char *p=ConvertFilename(cpu->DE.w);
     char path[FILENAME_MAX];
     FILE *fp;
     Z80Word addr;
@@ -278,9 +278,9 @@ static void LoadTape(Z80State *state)
 }
 
 
-static void SaveTape(Z80State *state)
+static void SaveTape(Z80 *cpu)
 {
-    const char *p=ConvertFilename(state->DE);
+    const char *p=ConvertFilename(cpu->DE.w);
     char path[FILENAME_MAX];
     FILE *fp;
     Z80Word start;
@@ -315,18 +315,14 @@ static void SaveTape(Z80State *state)
 
 static int EDCallback(Z80 *z80, Z80Val data)
 {
-    Z80State state;
-
-    Z80GetState(z80,&state);
-
     switch((Z80Byte)data)
     {
     	case 0xf0:
-	    SaveTape(&state);
+	    SaveTape(z80);
 	    break;
 
     	case 0xf1:
-	    LoadTape(&state);
+	    LoadTape(z80);
 	    break;
 
 	default:
@@ -339,7 +335,6 @@ static int EDCallback(Z80 *z80, Z80Val data)
 
 static void ULA_Video_Shifter(Z80 *z80, Z80Byte val)
 {
-    Z80State state;
     Z80Word base;
     int x,y;
     int inv;
@@ -348,8 +343,6 @@ static void ULA_Video_Shifter(Z80 *z80, Z80Byte val)
     if (!scr_enable)
     	return;
 
-    Z80GetState(z80,&state);
-
     /* Extra check due to out dodgy ULA emulation
     */
     if (ULA.y>=0 && ULA.y<SCR_H)
@@ -366,7 +359,7 @@ static void ULA_Video_Shifter(Z80 *z80, Z80Byte val)
 	inv=val&0x80;
 	val&=0x3f;
 
-	base=((Z80Word)state.I<<8)|(val<<3)|ULA.c;
+	base=((Z80Word)z80->I<<8)|(val<<3)|ULA.c;
 
 	if (inv)
 	{
@@ -394,29 +387,27 @@ static void ULA_Video_Shifter(Z80 *z80, Z80Byte val)
 
 static int CheckTimers(Z80 *z80, Z80Val val)
 {
-    if (val>HSYNC_PERIOD)
+    static Z80Byte last_R;
+
+    if (nmigen && val>NMI_PERIOD)
     {
-	Z80ResetCycles(z80,val-HSYNC_PERIOD);
+	Z80ResetCycles(z80,val-NMI_PERIOD);
 
-	if (nmigen && hsync)
-	{
-	    Z80NMI(z80);
-	    Debug("NMIGEN\n");
-	}
-	else if (hsync)
+	Z80NMI(z80);
+	/* Debug("NMI\n"); */
+    }
+
+    if (hsync)
+    {
+    	if (last_R&0x40 && !(z80->R&0x40))
 	{
-	    Debug("HSYNC\n");
 	    Z80Interrupt(z80,0xff);
-	    if (ULA.release)
-	    {
-	    	/* ULA.release=FALSE; */
-		ULA.c=(ULA.c+1)&7;
-		ULA.y++;
-		ULA.x=0;
-	    }
+	    /* Debug("INTERRUPT\n"); */
 	}
     }
 
+    last_R=z80->R;
+
     return TRUE;
 }
 
@@ -570,7 +561,7 @@ Z80Byte ZX81ReadPort(Z80 *z80, Z80Word port)
 {
     Z80Byte b=0;
 
-    Debug("IN  %4.4x\n",port);
+    /* Debug("IN  %4.4x\n",port); */
 
     switch(port&0xff)
     {
@@ -609,13 +600,13 @@ Z80Byte ZX81ReadPort(Z80 *z80, Z80Word port)
 	    */
 	    if (!vsync)
 	    {
-		Debug("VSYNC\n");
+		/* Debug("VSYNC\n"); */
 
 		GFXEndFrame(TRUE);
 		GFXClear(white);
 
 		ULA.x=0;
-		ULA.y=-1;
+		ULA.y=0;
 		ULA.c=7;
 		ULA.release=FALSE;
 
@@ -634,7 +625,7 @@ Z80Byte ZX81ReadPort(Z80 *z80, Z80Word port)
 	    */
 	    if (!nmigen)
 	    {
-		Debug("HSYNC OFF\n");
+		/* Debug("HSYNC OFF\n"); */
 	    	hsync=FALSE;
 	    }
 	    break;
@@ -649,7 +640,7 @@ Z80Byte ZX81ReadPort(Z80 *z80, Z80Word port)
 
 void ZX81WritePort(Z80 *z80, Z80Word port, Z80Byte val)
 {
-    Debug("OUT %4.4x,%2.2X\n",port,val);
+    /* Debug("OUT %4.4x,%2.2X\n",port,val); */
 
     /* Any port write releases the ULA line counter
     */
@@ -658,20 +649,20 @@ void ZX81WritePort(Z80 *z80, Z80Word port, Z80Byte val)
     switch(port&0xff)
     {
     	case 0xfd:	/* NMI generator OFF */
-	    Debug("NMIGEN OFF\n");
+	    /* Debug("NMIGEN OFF\n"); */
 	    nmigen=FALSE;
 	    break;
 
 	case 0xfe:	/* NMI generator ON */
-	    Debug("NMIGEN ON/VSYNC OFF\n");
+	    /* Debug("NMIGEN ON/VSYNC OFF\n"); */
 	    nmigen=TRUE;
 	    vsync=FALSE;
+	    Z80ResetCycles(z80,0);
 	    break;
 
 	case 0xff:	/* HSYNC generator ON */
-	    Debug("HSYNC ON\n");
+	    /* Debug("HSYNC ON\n"); */
 	    hsync=TRUE;
-	    Z80ResetCycles(z80,0);
 	    break;
     }
 }