/***************************************************************************
 *             __________               __   ___.
 *   Open      \______   \ ____   ____ |  | _\_ |__   _______  ___
 *   Source     |       _//  _ \_/ ___\|  |/ /| __ \ /  _ \  \/  /
 *   Jukebox    |    |   (  <_> )  \___|    < | \_\ (  <_> > <  <
 *   Firmware   |____|_  /\____/ \___  >__|_ \|___  /\____/__/\_ \
 *                     \/            \/     \/    \/            \/
 * $Id$
 *
 * Orginal from Vision-8 Emulator / Copyright (C) 1997-1999  Marcel de Kogel
 * Modified for Archos by Blueloop (a.wenger@gmx.de)
 *
 * All files in this archive are subject to the GNU General Public License.
 * See the file COPYING in the source tree root for full license agreement.
 *
 * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
 * KIND, either express or implied.
 *
 ****************************************************************************/
#include "plugin.h"

/* Only build for (correct) target */
#ifdef HAVE_LCD_BITMAP 

static struct plugin_api* rb; /* here is a global api struct pointer */

#define EXTERN static
#define STATIC static
#define memset rb->memset
#define memcpy rb->memcpy
#define printf DEBUGF
#define rand rb->rand
/* #define CHIP8_DEBUG */

#if (LCD_WIDTH >= 112) && (LCD_HEIGHT >= 64)
#define CHIP8_SUPER /* SCHIP even on the archos recorder (112x64) */
#endif

/****************************************************************************/
/**        (S)CHIP-8 core emulation, from Vision-8 + mods by Fdy           **/
/** The core is completely generic and can be used outside of Rockbox,     **/
/** thus the STATIC, EXTERN etc.  Please do not modify.                    **/
/****************************************************************************/
/** Vision8: CHIP8 emulator *************************************************/
/**                                                                        **/
/**                                CHIP8.h                                 **/
/**                                                                        **/
/** This file contains the portable CHIP8 emulation engine definitions     **/
/**                                                                        **/
/** Copyright (C) Marcel de Kogel 1997                                     **/
/**     You are not allowed to distribute this software commercially       **/
/**     Please, notify me, if you make any changes to this file            **/
/****************************************************************************/

#ifndef __CHIP8_H
#define __CHIP8_H

#ifndef EXTERN
#define EXTERN extern
#endif
 
typedef unsigned char byte;                     /* sizeof(byte)==1          */
typedef unsigned short word;                    /* sizeof(word)>=2          */

struct chip8_regs_struct
{
 byte alg[16];                                  /* 16 general registers     */
 byte delay,sound;                              /* delay and sound timer    */
 word i;                                        /* index register           */
 word pc;                                       /* program counter          */
 word sp;                                       /* stack pointer            */
};

EXTERN struct chip8_regs_struct chip8_regs;

#ifdef CHIP8_SUPER
#define CHIP8_WIDTH 128
#define CHIP8_HEIGHT 64
EXTERN byte chip8_super;	/* != 0 if in SCHIP display mode */
#else
#define CHIP8_WIDTH 64
#define CHIP8_HEIGHT 32
#endif

EXTERN byte chip8_iperiod;                      /* number of opcodes per    */
                                                /* timeslice (1/50sec.)     */
EXTERN byte chip8_keys[16];                     /* if 1, key is held down   */
EXTERN byte chip8_display[CHIP8_WIDTH*CHIP8_HEIGHT];/* 0xff if pixel is set,    */
                                                /* 0x00 otherwise           */
EXTERN byte chip8_mem[4096];                    /* machine memory. program  */
                                                /* is loaded at 0x200       */
EXTERN byte chip8_running;                      /* if 0, emulation stops    */

EXTERN void chip8_execute (void);                      /* execute chip8_iperiod    */
                                                /* opcodes                  */
EXTERN void chip8_reset (void);                        /* reset virtual machine    */
EXTERN void chip8 (void);                              /* start chip8 emulation    */

EXTERN void chip8_sound_on (void);                     /* turn sound on            */
EXTERN void chip8_sound_off (void);                    /* turn sound off           */
EXTERN void chip8_interrupt (void);                    /* update keyboard,         */
                                                /* display, etc.            */

#ifdef CHIP8_DEBUG
EXTERN byte chip8_trace;                        /* if 1, call debugger      */
                                                /* every opcode             */
EXTERN word chip8_trap;                         /* if pc==trap, set trace   */
                                                /* flag                     */
EXTERN void chip8_debug (word opcode,struct chip8_regs_struct *regs);
#endif

#endif          /* __CHIP8_H */

/** Vision8: CHIP8 emulator *************************************************/
/**                                                                        **/
/**                                CHIP8.c                                 **/
/**                                                                        **/
/** This file contains the portable CHIP8 emulation engine                 **/
/** SCHIP emulation (C) Frederic Devernay 2005                             **/
/**                                                                        **/
/** Copyright (C) Marcel de Kogel 1997                                     **/
/**     You are not allowed to distribute this software commercially       **/
/**     Please, notify me, if you make any changes to this file            **/
/****************************************************************************/

/* you can
   #define STATIC static
   #define EXTERN static
   and include this file for single-object generation
*/

#ifndef STATIC
#include <stdlib.h>		/* for memset, etc. */
#include <string.h>
#define STATIC
#endif

#ifdef CHIP8_DEBUG
#include <stdio.h>
#define DBG_(_x)       ((void)(_x))
#else
#define DBG_(_x)       ((void)0)
#endif

STATIC struct chip8_regs_struct chip8_regs;

static byte chip8_key_pressed;
STATIC byte chip8_keys[16];                     /* if 1, key is held down   */
STATIC byte chip8_display[CHIP8_WIDTH*CHIP8_HEIGHT]; /* 0xff if pixel is set,    */
                                                /* 0x00 otherwise           */
#ifdef CHIP8_SUPER
STATIC byte chip8_super;	/* != 0 if in SCHIP display mode */
#endif
STATIC byte chip8_mem[4096];                    /* machine memory. program  */
                                                /* is loaded at 0x200       */

#define read_mem(a)     (chip8_mem[(a)&4095])
#define write_mem(a,v)  (chip8_mem[(a)&4095]=(v))

STATIC byte chip8_iperiod;

STATIC byte chip8_running;                     /* Flag for End-of-Emulation */

#define get_reg_offset(opcode)          (chip8_regs.alg+(opcode>>8))
#define get_reg_value(opcode)           (*get_reg_offset(opcode))
#define get_reg_offset_2(opcode)        (chip8_regs.alg+((opcode>>4)&0x0f))
#define get_reg_value_2(opcode)         (*get_reg_offset_2(opcode))

typedef void (*opcode_fn) (word opcode);
typedef void (*math_fn) (byte *reg1,byte reg2);



static void op_call (word opcode)
{
    chip8_regs.sp--;
    write_mem (chip8_regs.sp,chip8_regs.pc&0xff);
    chip8_regs.sp--;
    write_mem (chip8_regs.sp,chip8_regs.pc>>8);
    chip8_regs.pc=opcode;
#ifdef CHIP8_DEBUG
    if(chip8_regs.sp < 0x1c0)
	printf("warning: more than 16 subroutine calls, sp=%x\n", chip8_regs.sp);
#endif
}

static void op_jmp (word opcode)
{
    chip8_regs.pc=opcode;
}

static void op_key (word opcode)
{
#ifdef CHIP8_DEBUG
    static byte tested[16] = {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0};
#endif
    byte key, key_value,cp_value;
    if ((opcode&0xff)==0x9e) /* skp */
        cp_value=1;
    else if ((opcode&0xff)==0xa1) /* sknp */
        cp_value=0;
    else {
	DBG_(printf("unhandled key opcode 0x%x\n", opcode));
	return;
    }
    key = get_reg_value(opcode)&0x0f;
#ifdef CHIP8_DEBUG
    if (!tested[key]) {
	tested[key] = 1;
	DBG_(printf("testing key %d\n", key));
    }
#endif
    key_value=chip8_keys[key];
    if (cp_value==key_value)
        chip8_regs.pc+=2;
}

static void op_skeq_const (word opcode)
{
    if (get_reg_value(opcode)==(opcode&0xff))
        chip8_regs.pc+=2;
}

static void op_skne_const (word opcode)
{
    if (get_reg_value(opcode)!=(opcode&0xff))
        chip8_regs.pc+=2;
}

static void op_skeq_reg (word opcode)
{
    if (get_reg_value(opcode)==get_reg_value_2(opcode))
        chip8_regs.pc+=2;
}

static void op_skne_reg (word opcode)
{
    if (get_reg_value(opcode)!=get_reg_value_2(opcode))
        chip8_regs.pc+=2;
}

static void op_mov_const (word opcode)
{
    *get_reg_offset(opcode)=opcode&0xff;
}

static void op_add_const (word opcode)
{
    *get_reg_offset(opcode)+=opcode&0xff;
}

static void op_mvi (word opcode)
{
    chip8_regs.i=opcode;
}

static void op_jmi (word opcode)
{
    chip8_regs.pc=opcode+chip8_regs.alg[0];
}

static void op_rand (word opcode)
{
    *get_reg_offset(opcode)=rand()&(opcode&0xff);
}

static void math_or (byte *reg1,byte reg2)
{
    *reg1|=reg2;
}

static void math_mov (byte *reg1,byte reg2)
{
    *reg1=reg2;
}

static void math_nop (byte *reg1,byte reg2)
{
    (void)reg1;
    (void)reg2;
    DBG_(printf("Warning: math nop!\n"));
}

static void math_and (byte *reg1,byte reg2)
{
    *reg1&=reg2;
}

static void math_xor (byte *reg1,byte reg2)
{
 *reg1^=reg2;
}

static void math_add (byte *reg1,byte reg2)
{
    word tmp;
    tmp=*reg1+reg2;
    *reg1=(byte)tmp;
    chip8_regs.alg[15]=tmp>>8;
}

static void math_sub (byte *reg1,byte reg2)
{
    word tmp;
    tmp=*reg1-reg2;
    *reg1=(byte)tmp;
    chip8_regs.alg[15]=((byte)(tmp>>8))+1;
}

static void math_shr (byte *reg1,byte reg2)
{
    (void)reg2;
    chip8_regs.alg[15]=*reg1&1;
    *reg1>>=1;
}

static void math_shl (byte *reg1,byte reg2)
{
    (void)reg2;
    chip8_regs.alg[15]=*reg1>>7;
    *reg1<<=1;
}

static void math_rsb (byte *reg1,byte reg2)
{
    word tmp;
    tmp=reg2-*reg1;
    *reg1=(byte)tmp;
    chip8_regs.alg[15]=((byte)(tmp>>8))+1;
}

#ifdef CHIP8_SUPER
/* SUPER: scroll down n lines (or half in CHIP8 mode) */
static void scroll_down(word opcode)
{
    int n = opcode & 0xf;
    byte *dst = chip8_display + CHIP8_WIDTH*CHIP8_HEIGHT -1;
    byte *src = dst - n*CHIP8_WIDTH;
    while(src >= chip8_display) {
	*dst-- = *src--;
    }
    while(dst >= chip8_display) {
	*dst-- = 0;
    }
}
/* SUPER: scroll 4 pixels left! */
static void scroll_left(void)
{
    byte *dst = chip8_display;
    byte *src = dst;
    byte *eol = chip8_display + CHIP8_WIDTH;
    byte *eoi = chip8_display + CHIP8_WIDTH*CHIP8_HEIGHT;
    while(eol <= eoi) {
	src+=4;
	while(src < eol) {
	    *dst++ = *src++;
	}
	*dst++ = 0;
	*dst++ = 0;
	*dst++ = 0;
	*dst++ = 0;
	eol += CHIP8_WIDTH;
    }
}
static void scroll_right(void)
{
    byte *dst = chip8_display + CHIP8_WIDTH*CHIP8_HEIGHT -1;
    byte *src = dst;
    byte *bol = chip8_display + CHIP8_WIDTH*(CHIP8_HEIGHT-1);
    while(bol >= chip8_display) {
	src-=4;
	while(src >= bol) {
	    *dst-- = *src--;
	}
	*dst-- = 0;
	*dst-- = 0;
	*dst-- = 0;
	*dst-- = 0;
	bol -= CHIP8_WIDTH;
    }
}
#endif

static void op_system (word opcode)
{
    switch ((byte)opcode)
    {
#ifdef CHIP8_SUPER
    case 0xfb:
	scroll_right();
	break;
    case 0xfc:
	scroll_left();
	break;	
    case 0xfd:
	DBG_(printf("SUPER: quit the emulator\n"));
	chip8_reset();
	break;	
    case 0xfe:
	DBG_(printf("SUPER: set CHIP-8 graphic mode\n"));
	memset (chip8_display,0,sizeof(chip8_display));
	chip8_super = 0;
	break;
    case 0xff:
	DBG_(printf("SUPER: set SCHIP graphic mode\n"));
	memset (chip8_display,0,sizeof(chip8_display));
	chip8_super = 1;
	break;	
#endif
        case 0xe0:
            memset (chip8_display,0,sizeof(chip8_display));
            break;
        case 0xee:
            chip8_regs.pc=read_mem(chip8_regs.sp)<<8;
            chip8_regs.sp++;
            chip8_regs.pc+=read_mem(chip8_regs.sp);
            chip8_regs.sp++;
            break;
    default:
#ifdef CHIP8_SUPER
	if ((opcode & 0xF0) == 0xC0)
	    scroll_down(opcode);
	else
#endif
	{
	    DBG_(printf("unhandled system opcode 0x%x\n", opcode));
	    chip8_running = 3;
	}
	break;
    }
}

static void op_misc (word opcode)
{
    byte *reg,i,j;
#ifdef CHIP8_DEBUG
    static byte firstwait = 1;
#endif
    reg=get_reg_offset(opcode);
    switch ((byte)opcode)
    {
        case 0x07:		/* gdelay */
            *reg=chip8_regs.delay;
            break;
        case 0x0a:		/* key */
#ifdef CHIP8_DEBUG
	    if(firstwait) {
		printf("waiting for key press\n");
		firstwait = 0;
	    }
#endif
	    if (chip8_key_pressed)
                *reg=chip8_key_pressed-1;
            else
                chip8_regs.pc-=2;
            break;
        case 0x15:		/* sdelay */
            chip8_regs.delay=*reg;
            break;
        case 0x18:		/* ssound */
            chip8_regs.sound=*reg;
            if (chip8_regs.sound)
                chip8_sound_on();
            break;
        case 0x1e:		/* adi */
            chip8_regs.i+=(*reg);
            break;
        case 0x29:		/* font */
            chip8_regs.i=((word)(*reg&0x0f))*5;
            break;
#ifdef CHIP8_SUPER
    case 0x30:			/* xfont */
            chip8_regs.i=((word)(*reg&0x0f))*10+0x50;
	    break;
#endif
        case 0x33:		/* bcd */
            i=*reg;
            for (j=0;i>=100;i-=100)
                j++;
            write_mem (chip8_regs.i,j);
            for (j=0;i>=10;i-=10)
                j++;
            write_mem (chip8_regs.i+1,j);
            write_mem (chip8_regs.i+2,i);
            break;
        case 0x55:		/* str */
            for (i=0,j=(opcode>>8)&0x0f; i<=j; ++i)
                write_mem(chip8_regs.i+i,chip8_regs.alg[i]);
            break;
        case 0x65:		/* ldr */
            for (i=0,j=(opcode>>8)&0x0f; i<=j; ++i)
                chip8_regs.alg[i]=read_mem(chip8_regs.i+i);
            break;
#ifdef CHIP8_SUPER
    case 0x75:
	DBG_(printf("SUPER: save V0..V%x (X<8) in the HP48 flags\n", (opcode>>8)&0x0f));
	break;
    case 0x85:
	DBG_(printf("SUPER: load V0..V%x (X<8) from the HP48 flags\n", (opcode>>8)&0x0f));
	break;
#endif
    default:
	DBG_(printf("unhandled misc opcode 0x%x\n", opcode));
	break;
    }
}

static void op_sprite (word opcode)
{
    byte *q;
    byte n,x,x2,y,collision;
    word p;
    x=get_reg_value(opcode);
    y=get_reg_value_2(opcode);
    p=chip8_regs.i;
    n=opcode&0x0f;
#ifdef CHIP8_SUPER
    if (chip8_super) {
	/*printf("SUPER: sprite(%x)\n", opcode);*/
	x &= 128-1;
	y &= 64-1;
	q=chip8_display+y*CHIP8_WIDTH;
	if(n == 0)
	{		/* 16x16 sprite */
	    n = 16;
	    if (n+y>64)
		n=64-y;
	    for (collision=1;n;--n,q+=CHIP8_WIDTH)
	    {
		/* first 8 bits */
		for (y=read_mem(p++),x2=x;y;y<<=1,x2=(x2+1)&(CHIP8_WIDTH-1))
		    if (y&0x80)
			collision&=(q[x2]^=0xff);
		x2=(x+8)&(CHIP8_WIDTH-1);
		/* last 8 bits */
		for (y=read_mem(p++);y;y<<=1,x2=(x2+1)&(CHIP8_WIDTH-1))
		    if (y&0x80)
			collision&=(q[x2]^=0xff);
	    }
	}
	else {
	    /* 8xn sprite */
	    if (n+y>64)
		n=64-y;
	    for (collision=1;n;--n,q+=CHIP8_WIDTH)
	    {
		for (y=read_mem(p++),x2=x;y;y<<=1,x2=(x2+1)&(CHIP8_WIDTH-1))
		    if (y&0x80)
			collision&=(q[x2]^=0xff);
	    }
	}
    }
    else {
	x &= 64-1;
	y &= 32-1;
	q=chip8_display+y*CHIP8_WIDTH*2;
	if(n == 0) 
	    n = 16;
	if (n+y>32)
	    n=32-y;
	for (collision=1;n;--n,q+=CHIP8_WIDTH*2)
	{
	    for (y=read_mem(p++),x2=x*2;y;y<<=1,x2=(x2+2)&(CHIP8_WIDTH-1))
		if (y&0x80) {
		    q[x2]^=0xff;
		    q[x2+1]^=0xff;
		    q[x2+CHIP8_WIDTH]^=0xff;
		    q[x2+CHIP8_WIDTH+1]^=0xff;
		    collision &= q[x2]|q[x2+1]|q[x2+CHIP8_WIDTH]|q[x2+CHIP8_WIDTH+1];
		}
	}
    }
#else
    x &= 64-1;
    y &= 32-1;
    q=chip8_display+y*CHIP8_WIDTH;
    if (n+y>32)
        n=32-y;
    for (collision=1;n;--n,q+=CHIP8_WIDTH)
    {
        for (y=read_mem(p++),x2=x;y;y<<=1,x2=(x2+1)&(CHIP8_WIDTH-1))
            if (y&0x80)
		collision&=(q[x2]^=0xff);
    }
#endif
    chip8_regs.alg[15]=collision^1;
}

static math_fn math_opcodes[16]=
{
    math_mov,
    math_or,
    math_and,
    math_xor,
    math_add,
    math_sub,
    math_shr,
    math_rsb,
    math_nop,
    math_nop,
    math_nop,
    math_nop,
    math_nop,
    math_nop,
    math_shl,
    math_nop
};

static void op_math (word opcode)
{
    (*(math_opcodes[opcode&0x0f]))
        (get_reg_offset(opcode),get_reg_value_2(opcode));
}

static opcode_fn main_opcodes[16]=
{
    op_system,
    op_jmp,
    op_call,
    op_skeq_const,
    op_skne_const,
    op_skeq_reg,
    op_mov_const,
    op_add_const,
    op_math,
    op_skne_reg,
    op_mvi,
    op_jmi,
    op_rand,
    op_sprite,
    op_key,
    op_misc
};

#ifdef CHIP8_DEBUG
STATIC byte chip8_trace;
STATIC word chip8_trap;

/****************************************************************************/
/* This routine is called every opcode when chip8_trace==1. It prints the   */
/* current register contents and the opcode being executed                  */
/****************************************************************************/
STATIC void chip8_debug (word opcode,struct chip8_regs_struct *regs)
{
    int i;
    byte hextable[16] = "0123456789ABCDEF";
    byte v1[3] = "Vx\0";
    byte v2[3] = "Vx\0";
    v1[1] = hextable[(opcode>>8)&0x0f];
    v2[1] = hextable[(opcode>>8)&0x0f];
    printf ("PC=%04X: %04X - ",regs->pc,opcode);
    switch (opcode>>12) {
    case 0:
	if ((opcode&0xff0) == 0xc0) {
	    printf ("SCD  %01X       ; Scroll down n lines",opcode&0xf);
	}
	else switch (opcode&0xfff) {
	case 0xe0:
	    printf ("CLS          ; Clear screen");
	    break;
	case 0xee:
	    printf ("RET          ; Return from subroutine call");
	    break;
	case 0xfb:
	    printf("SCR           ; Scroll right");
	    break;
	case 0xfc:
	    printf("SCL           ; Scroll left");
	    break;
	case 0xfd:
	    printf("EXIT          ; Terminate the interpreter");
	    break;
	case 0xfe:
	    printf("LOW           ; Disable extended screen mode");
	    break;
	case 0xff:
	    printf("HIGH          ; Enable extended screen mode");
	    break;
	default:
	    printf ("SYS  %03X     ; Unknown system call",opcode&0xff);
	}
	break;
    case 1:
	printf ("JP   %03X     ; Jump to address",opcode&0xfff);
	break;
    case 2:
	printf ("CALL %03X     ; Call subroutine",opcode&0xfff);
	break;
    case 3:
	printf ("SE   %s,%02X   ; Skip if register == constant",v1,opcode&0xff);
	break;
    case 4:
	printf ("SNE  %s,%02X   ; Skip if register <> constant",v1,opcode&0xff);
	break;
    case 5:
	printf ("SE   %s,%s   ; Skip if register == register",v1,v2);
	break;
    case 6:
	printf ("LD   %s,%02X   ; Set VX = Byte",v1,opcode&0xff);
	break;
    case 7:
	printf ("ADD  %s,%02X   ; Set VX = VX + Byte",v1,opcode&0xff);
	break;
    case 8:
	switch (opcode&0x0f) {
	case 0:
	    printf ("LD   %s,%s   ; Set VX = VY, VF updates",v1,v2);
	    break;
	case 1:
	    printf ("OR   %s,%s   ; Set VX = VX | VY, VF updates",v1,v2);
	    break;
	case 2:
	    printf ("AND  %s,%s   ; Set VX = VX & VY, VF updates",v1,v2);
	    break;
	case 3:
	    printf ("XOR  %s,%s   ; Set VX = VX ^ VY, VF updates",v1,v2);
	    break;
	case 4:
	    printf ("ADD  %s,%s   ; Set VX = VX + VY, VF = carry",v1,v2);
	    break;
	case 5:
	    printf ("SUB  %s,%s   ; Set VX = VX - VY, VF = !borrow",v1,v2);
	    break;
	case 6:
	    printf ("SHR  %s,%s   ; Set VX = VX >> 1, VF = carry",v1,v2);
	    break;
	case 7:
	    printf ("SUBN %s,%s   ; Set VX = VY - VX, VF = !borrow",v1,v2);
	    break;
	case 14:
	    printf ("SHL  %s,%s   ; Set VX = VX << 1, VF = carry",v1,v2);
	    break;
	default:
	    printf ("Illegal opcode");
	}
	break;
    case 9:
	printf ("SNE  %s,%s   ; Skip next instruction iv VX!=VY",v1,v2);
	break;
    case 10:
	printf ("LD   I,%03X   ; Set I = Addr",opcode&0xfff);
	break;
    case 11:
	printf ("JP   V0,%03X  ; Jump to Addr + V0",opcode&0xfff);
	break;
    case 12:
	printf ("RND  %s,%02X   ; Set VX = random & Byte",v1,opcode&0xff);
	break;
    case 13:
	printf ("DRW  %s,%s,%X ; Draw n byte sprite stored at [i] at VX,VY. Set VF = collision",v1,v2,opcode&0x0f);
	break;
    case 14:
	switch (opcode&0xff) {
	case 0x9e:
	    printf ("SKP  %s      ; Skip next instruction if key VX down",v1);
	    break;
	case 0xa1:
	    printf ("SKNP %s      ; Skip next instruction if key VX up",v1);
	    break;
	default:
	    printf ("%04X        ; Illegal opcode", opcode);
	}
	break;
    case 15:
	switch (opcode&0xff) {
	case 0x07:
	    printf ("LD   %s,DT   ; Set VX = delaytimer",v1);
	    break;
	case 0x0a:
	    printf ("LD   %s,K    ; Set VX = key, wait for keypress",v1);
	    break;
	case 0x15:
	    printf ("LD   DT,%s   ; Set delaytimer = VX",v1);
	    break;
	case 0x18:
	    printf ("LD   ST,%s   ; Set soundtimer = VX",v1);
	    break;
	case 0x1e:
	    printf ("ADD  I,%s    ; Set I = I + VX",v1);
	    break;
	case 0x29:
	    printf ("LD  LF,%s    ; Point I to 5 byte numeric sprite for value in VX",v1);
	    break;
	case 0x30:
	    printf ("LD  HF,%s    ; Point I to 10 byte numeric sprite for value in VX",v1);
	    break;
	case 0x33:
	    printf ("LD   B,%s    ; Store BCD of VX in [I], [I+1], [I+2]",v1);
	    break;
	case 0x55:
	    printf ("LD   [I],%s  ; Store V0..VX in [I]..[I+X]",v1);
	    break;
	case 0x65:
	    printf ("LD   %s,[I]  ; Read V0..VX from [I]..[I+X]",v1);
	    break;
	case 0x75:
	    printf ("LD   R,%s    ; Store V0..VX in RPL user flags (X<=7)",v1);
	    break;
	case 0x85:
	    printf ("LD   %s,R    ; Read V0..VX from RPL user flags (X<=7)",v1);
	    break;
	default:
	    printf ("%04X        ; Illegal opcode", opcode);
	}
	break;
    }
    printf ("\n; Registers: ");
    for (i=0;i<16;++i) printf ("%02x ",(regs->alg[i])&0xff);
    printf ("\n; Index: %03x Stack:%03x Delay:%02x Sound:%02x\n",
	    regs->i&0xfff,regs->sp&0xfff,regs->delay&0xff,regs->sound&0xff);
}
#endif

/****************************************************************************/
/* Execute chip8_iperiod opcodes                                            */
/****************************************************************************/
STATIC void chip8_execute(void)
{
    byte i;
    byte key_pressed=0;
    word opcode;
    for (i = chip8_iperiod ; i ;--i)
    {
	/* Fetch the opcode */
        opcode=(read_mem(chip8_regs.pc)<<8)+read_mem(chip8_regs.pc+1);
#ifdef CHIP8_DEBUG
	/* Check if trap address has been reached */
	if ((chip8_regs.pc&4095)==chip8_trap)
	    chip8_trace=1;
	/* Call the debugger if chip8_trace!=0 */
	if (chip8_trace)
	    chip8_debug (opcode,&chip8_regs);
#endif
        chip8_regs.pc+=2;
        (*(main_opcodes[opcode>>12]))(opcode&0x0fff); /* Emulate this opcode */
    }
    /* Update timers */
    if (chip8_regs.delay)
        --chip8_regs.delay;
    if (chip8_regs.sound)
        if (--chip8_regs.sound == 0)
            chip8_sound_off();       

    /* Update the machine status */
    chip8_interrupt ();

    for (i=key_pressed=0;i<16;++i)              /* check if a key was first */
        if (chip8_keys[i])	                /* pressed                  */
            key_pressed=i+1;
    if (key_pressed && key_pressed!=chip8_key_pressed)
        chip8_key_pressed=key_pressed;
    else
        chip8_key_pressed=0;
}

/****************************************************************************/
/* Reset the virtual chip8 machine                                          */
/****************************************************************************/
STATIC void chip8_reset(void)
{
    static byte chip8_sprites[0x50]=
     {
         0xf9,0x99,0xf2,0x62,0x27,
         0xf1,0xf8,0xff,0x1f,0x1f,
         0x99,0xf1,0x1f,0x8f,0x1f,
         0xf8,0xf9,0xff,0x12,0x44,
         0xf9,0xf9,0xff,0x9f,0x1f,
         0xf9,0xf9,0x9e,0x9e,0x9e,
         0xf8,0x88,0xfe,0x99,0x9e,
         0xf8,0xf8,0xff,0x8f,0x88,
     }; /* 4x5 pixel hexadecimal character font patterns */
#ifdef CHIP8_SUPER
    static byte schip_sprites[10*10]=
     {
	 0x3C, 0x7E, 0xC3, 0xC3, 0xC3, 0xC3, 0xC3, 0xC3, 0x7E, 0x3C, /* 0 */
	 0x18, 0x38, 0x58, 0x18, 0x18, 0x18, 0x18, 0x18, 0x18, 0x3C, /* 1 */
	 0x3E, 0x7F, 0xC3, 0x06, 0x0C, 0x18, 0x30, 0x60, 0xFF, 0xFF, /* 2 */
	 0x3C, 0x7E, 0xC3, 0x03, 0x0E, 0x0E, 0x03, 0xC3, 0x7E, 0x3C, /* 3 */
	 0x06, 0x0E, 0x1E, 0x36, 0x66, 0xC6, 0xFF, 0xFF, 0x06, 0x06, /* 4 */
	 0xFF, 0xFF, 0xC0, 0xC0, 0xFC, 0xFE, 0x03, 0xC3, 0x7E, 0x3C, /* 5 */
	 0x3E, 0x7C, 0xC0, 0xC0, 0xFC, 0xFE, 0xC3, 0xC3, 0x7E, 0x3C, /* 6 */
	 0xFF, 0xFF, 0x03, 0x06, 0x0C, 0x18, 0x30, 0x60, 0x60, 0x60, /* 7 */
	 0x3C, 0x7E, 0xC3, 0xC3, 0x7E, 0x7E, 0xC3, 0xC3, 0x7E, 0x3C, /* 8 */
	 0x3C, 0x7E, 0xC3, 0xC3, 0x7F, 0x3F, 0x03, 0x03, 0x3E, 0x7C, /* 9 */
     }; /* 8x10 pixel font patterns (only 10) */
#endif
    byte i;
    for (i=0;i<16*5;++i)
    {
        write_mem (i<<1,chip8_sprites[i]&0xf0);
        write_mem ((i<<1)+1,chip8_sprites[i]<<4);
    }
#ifdef CHIP8_SUPER
    /*
    for (i=0; i<100; i++)
        write_mem (i+0x50,schip_sprites[i]);
    */
    memcpy(chip8_mem+0x50, schip_sprites, 100);
    chip8_super = 0;
#endif
    memset (chip8_regs.alg,0,sizeof(chip8_regs.alg));
    memset (chip8_keys,0,sizeof(chip8_keys));
    chip8_key_pressed=0;
    memset (chip8_display,0,sizeof(chip8_display));
    chip8_regs.delay=chip8_regs.sound=chip8_regs.i=0;
    chip8_regs.sp=0x1e0;
    chip8_regs.pc=0x200;
    chip8_sound_off ();
    chip8_running=1;
#ifdef CHIP8_DEBUG
    chip8_trace=0;
#endif
}


/****************************************************************************/
/* Start CHIP8 emulation                                                    */
/****************************************************************************/
STATIC void chip8 (void)
{
 chip8_reset ();
 while (chip8_running==1) chip8_execute ();
}

/****************************************************************************/
/** END OF (S)CHIP-8 core emulation, from Vision-8 + mods by Fdy           **/
/****************************************************************************/

/* size of the displayed area */
#if (CHIP8_WIDTH == 128) && (LCD_WIDTH < 128)
#define CHIP8_LCDWIDTH 112
#else
#define CHIP8_LCDWIDTH CHIP8_WIDTH
#endif

#if (LCD_WIDTH > CHIP8_LCDWIDTH)
#define CHIP8_X ((LCD_WIDTH - CHIP8_LCDWIDTH)/2)
#else
#define CHIP8_X 0
#endif
#if (LCD_HEIGHT > CHIP8_HEIGHT)
#define CHIP8_Y (((LCD_HEIGHT - CHIP8_HEIGHT)>>4)<<3)
#else
#define CHIP8_Y 0
#endif

/* variable button definitions */
#if CONFIG_KEYPAD == RECORDER_PAD /* only 9 out of 16 chip8 buttons */
#define CHIP8_KEY1 BUTTON_F1
#define CHIP8_KEY2 BUTTON_UP
#define CHIP8_KEY3 BUTTON_F3
#define CHIP8_KEY4 BUTTON_LEFT
#define CHIP8_KEY5 BUTTON_PLAY
#define CHIP8_KEY6 BUTTON_RIGHT
#define CHIP8_KEY7 BUTTON_F2
#define CHIP8_KEY8 BUTTON_DOWN
#define CHIP8_KEY9 BUTTON_ON

#elif CONFIG_KEYPAD == ONDIO_PAD /* even more limited */
#define CHIP8_KEY2 BUTTON_UP
#define CHIP8_KEY4 BUTTON_LEFT
#define CHIP8_KEY5 BUTTON_MENU
#define CHIP8_KEY6 BUTTON_RIGHT
#define CHIP8_KEY8 BUTTON_DOWN

#elif (CONFIG_KEYPAD == IRIVER_H100_PAD) || \
      (CONFIG_KEYPAD == IRIVER_H300_PAD)
#define CHIP8_KEY2 BUTTON_UP
#define CHIP8_KEY4 BUTTON_LEFT
#define CHIP8_KEY5 BUTTON_SELECT
#define CHIP8_KEY6 BUTTON_RIGHT
#define CHIP8_KEY8 BUTTON_DOWN

#endif

static byte chip8_virtual_keys[16];
static byte chip8_keymap[16];

static unsigned long starttimer; /* Timer value at the beginning */
static unsigned long cycles; /* Number of update cycles (50Hz) */

#ifndef SIMULATOR
static bool is_playing;
#endif

/* one frame of bitswapped mp3 data */
static unsigned char beep[]={255,
223, 28, 35,  0,192,210, 35,226, 72,188,242,  1,128,166, 16, 68,146,252,151, 19,
 10,180,245,127, 96,184,  3,184, 30,  0,118, 59,128,121,102,  6,212,  0, 97,  6,
 42, 65, 28,134,192,145, 57, 38,136, 73, 29, 38,132, 15, 21, 70, 91,185, 99,198,
 15,192, 83,  6, 33,129, 20,  6, 97, 33,  4,  6,245,128, 92,  6, 24,  0, 86,  6,
 56,129, 44, 24,224, 25, 13, 48, 50, 82,180, 11,251,106,249, 59, 24, 82,175,223,
252,119, 76,134,120,236,149,250,247,115,254,145,173,174,168,180,255,107,195, 89,
 24, 25, 48,131,192, 61, 48, 64, 10,176, 49, 64,  1,152, 50, 32,  8,140, 48, 16,
  5,129, 51,196,187, 41,177, 23,138, 70, 50,  8, 10,242, 48,192,  3,248,226,  0,
 20,100, 18, 96, 41, 96, 78,102,  7,201,122, 76,119, 20,137, 37,177, 15,132,224,
 20, 17,191, 67,147,187,116,211, 41,169, 63,172,182,186,217,155,111,140,104,254,
111,181,184,144, 17,148, 21,101,166,227,100, 86, 85, 85, 85}; 

/* callback to request more mp3 data */
void callback(unsigned char** start, int* size)
{
    *start = beep; /* give it the same frame again */
    *size = sizeof(beep);
}

/****************************************************************************/
/* Turn sound on                                                            */
/****************************************************************************/
static void chip8_sound_on (void) 
{
#ifndef SIMULATOR
    if (!is_playing)
        rb->mp3_play_pause(true); /* kickoff audio */
#endif
}

/****************************************************************************/
/* Turn sound off                                                           */
/****************************************************************************/
static void chip8_sound_off (void) 
{ 
#ifndef SIMULATOR
    if (!is_playing)
        rb->mp3_play_pause(false); /* pause audio */
#endif
}

/****************************************************************************/
/* Update the display                                                       */
/****************************************************************************/
static void chip8_update_display(void)
{
    int x, lcd_x, y, i;
    byte w;
    byte* row;
    /* frame buffer in hardware fomat */
    unsigned char lcd_framebuf[CHIP8_HEIGHT/8][CHIP8_LCDWIDTH];

    for (y=0;y<CHIP8_HEIGHT/8;++y)
    {
        row = lcd_framebuf[y];
        for (x=0, lcd_x=0;x<CHIP8_WIDTH;++x,++lcd_x)
        {
            w = 0;
            for (i=0;i<8;i++)
            {
                w = w >> 1;
                if (chip8_display[x+(y*8+i)*CHIP8_WIDTH] != 0)
                {
                    w += 128;
                }
            }
#if (CHIP8_LCDWIDTH < 128)              /* LCD_WIDTH between 112 and 127 */
            if (x%8 == 1) {
                row[-1] |= w;   /* overlay on */
            }
            else
#endif
                *row++ = w;
        }
    }
#if defined(SIMULATOR) || (LCD_DEPTH > 1)
    rb->lcd_set_drawmode(DRMODE_SOLID);
    rb->lcd_mono_bitmap(lcd_framebuf[0], CHIP8_X, CHIP8_Y, CHIP8_LCDWIDTH, CHIP8_HEIGHT);
    rb->lcd_update();
#else
    rb->lcd_blit(lcd_framebuf[0], CHIP8_X, CHIP8_Y>>3, CHIP8_LCDWIDTH, CHIP8_HEIGHT>>3
                 , CHIP8_LCDWIDTH);
#endif
}

static void chip8_keyboard(void)
{
    int i;
    int button = rb->button_get(false);
    switch (button)
    {
    case BUTTON_OFF:                                      /* Abort Emulator */
        chip8_running = 0;
        break;

    case CHIP8_KEY2:                chip8_virtual_keys[2] = 1; break;
    case CHIP8_KEY2 | BUTTON_REL:   chip8_virtual_keys[2] = 0; break;
    case CHIP8_KEY4:                chip8_virtual_keys[4] = 1; break;
    case CHIP8_KEY4 | BUTTON_REL:   chip8_virtual_keys[4] = 0; break;
    case CHIP8_KEY6:                chip8_virtual_keys[6] = 1; break;
    case CHIP8_KEY6 | BUTTON_REL:   chip8_virtual_keys[6] = 0; break;
    case CHIP8_KEY8:                chip8_virtual_keys[8] = 1; break;
    case CHIP8_KEY8 | BUTTON_REL:   chip8_virtual_keys[8] = 0; break;
    case CHIP8_KEY5:                chip8_virtual_keys[5] = 1; break;
    case CHIP8_KEY5 | BUTTON_REL:   chip8_virtual_keys[5] = 0; break;
#ifdef CHIP8_KEY1
    case CHIP8_KEY1:                chip8_virtual_keys[1] = 1; break;
    case CHIP8_KEY1 | BUTTON_REL:   chip8_virtual_keys[1] = 0; break;
#endif
#ifdef CHIP8_KEY3
    case CHIP8_KEY3:                chip8_virtual_keys[3] = 1; break;
    case CHIP8_KEY3 | BUTTON_REL:   chip8_virtual_keys[3] = 0; break;
#endif
#ifdef CHIP8_KEY7
    case CHIP8_KEY7:                chip8_virtual_keys[7] = 1; break;
    case CHIP8_KEY7 | BUTTON_REL:   chip8_virtual_keys[7] = 0; break;
#endif
#ifdef CHIP8_KEY9
    case CHIP8_KEY9:                chip8_virtual_keys[9] = 1; break;
    case CHIP8_KEY9 | BUTTON_REL:   chip8_virtual_keys[9] = 0; break;
#endif

    default:
        if (rb->default_event_handler(button) == SYS_USB_CONNECTED)
            chip8_running = 2; /* indicates stopped because of USB */
        break;
    }
    for(i=0; i<16; i++) {
        chip8_keys[i] = chip8_virtual_keys[chip8_keymap[i]];
    }
}

/****************************************************************************/
/* Update keyboard and display, sync emulation with VDP clock               */
/****************************************************************************/
static void chip8_interrupt (void)
{
    unsigned long newtimer;
    unsigned long timer, runtime;

    chip8_update_display();
    chip8_keyboard();
    cycles ++;
    runtime = cycles * HZ / 50;
    timer = starttimer + runtime;
    newtimer = *rb->current_tick;
    if (TIME_AFTER(timer, newtimer))
    {
	rb->sleep(timer - newtimer);
    }
    else
    {
	rb->yield();
    }
    starttimer = newtimer - runtime;
}

static bool chip8_init(char* file)
{
    int numread;
    int fd;
    int len;
    int i;

    fd = rb->open(file, O_RDONLY);
    if (fd==-1) {
	rb->lcd_puts(0, 6, "File Error.");
	return false;
    }
    numread = rb->read(fd, chip8_mem+0x200, 4096-0x200);
    if (numread==-1) {
	rb->lcd_puts(0, 6, "I/O Error.");
	return false;
    }

    rb->close(fd);
    /* is there a c8k file (chip8 keys) ? */
    for(i=0; i<16; i++) {
	chip8_virtual_keys[i] = 0;
	chip8_keymap[i] = i;
    }
    len = rb->strlen(file);
    file[len-2] = '8';
    file[len-1] = 'k';
    fd = rb->open(file, O_RDONLY);
    if (fd!=-1) {
	rb->lcd_puts(0, 6, "File&Keymap OK.");
	numread = rb->read(fd, chip8_keymap, 16);
	rb->close(fd);
    }
    else
    {
	rb->lcd_puts(0, 6, "File OK.");
    }
    for(i=0; i<16; i++) {
	if (chip8_keymap[i] >= '0'
	    && chip8_keymap[i] <= '9')
	    chip8_keymap[i] -= '0';
	else if (chip8_keymap[i] >= 'A'
	    && chip8_keymap[i] <= 'F')
	    chip8_keymap[i] -= 'A' - 10;
	else if (chip8_keymap[i] >= 'a'
	    && chip8_keymap[i] <= 'f')
	    chip8_keymap[i] -= 'a' - 10;
	else
	    chip8_keymap[i] %= 16;
    }
    return true;
}

bool chip8_run(char* file)
{
    int ok;

    rb->lcd_clear_display();
    rb->lcd_puts(0, 0, "SChip8 Emulator");
    rb->lcd_puts(0, 1, "    (c) by     ");
    rb->lcd_puts(0, 2, "Marcel de Kogel");
    rb->lcd_puts(0, 3, "    Rockbox:   ");
    rb->lcd_puts(0, 4, "  Blueloop/Fdy ");
    rb->lcd_puts(0, 5, "---------------");
    ok = chip8_init(file);
    rb->lcd_update();
    rb->sleep(HZ*1);
    if (!ok)
        return false;
    rb->lcd_clear_display();
#if (CHIP8_X > 0) && (CHIP8_Y > 0)
    rb->lcd_drawrect(CHIP8_X-1,CHIP8_Y-1,CHIP8_LCDWIDTH+2,CHIP8_HEIGHT+2);
#endif
    rb->lcd_update();

#ifndef SIMULATOR
    /* init sound */
    is_playing = rb->mp3_is_playing(); /* would we disturb playback? */
    if (!is_playing) /* no? then we can make sound */
    {   /* prepare */
        rb->mp3_play_data(beep, sizeof(beep), callback);
    }
#endif
    starttimer = *rb->current_tick;

    chip8_iperiod=15;
    cycles = 0;
    chip8();

    if (!ok) {
        rb->splash(HZ, true, "Error");
        return false;
    }

#ifndef SIMULATOR
    if (!is_playing)
    {   /* stop it if we used audio */
        rb->mp3_play_stop(); /* Stop audio playback */
    }
#endif

    if (chip8_running == 3) {
	/* unsupported instruction */
        rb->splash(HZ, true, "Error: Unsupported"
#ifndef CHIP8_SUPER
	" CHIP-8 instruction. (maybe S-CHIP)"
#else
        " (S)CHIP-8 instruction."
#endif
            );
        return false;
    }

    return true;
}


/***************** Plugin Entry Point *****************/

enum plugin_status plugin_start(struct plugin_api* api, void* parameter)
{
    char* filename;

    /* this macro should be called as the first thing you do in the plugin.
       it test that the api version and model the plugin was compiled for
       matches the machine it is running on */
    TEST_PLUGIN_API(api);
    rb = api; /* copy to global api pointer */

    if (parameter == NULL)
    {
        rb->splash(HZ, true, "Play a .ch8 file!");
        return PLUGIN_ERROR;
    }
    else
    {
        filename = (char*) parameter; 
    }

    /* now go ahead and have fun! */
    if (chip8_run(filename))
        if (chip8_running == 0)
            return PLUGIN_OK;
        else
            return PLUGIN_USB_CONNECTED;
    else
        return PLUGIN_ERROR;
}
#endif /* #ifdef HAVE_LCD_BITMAP */
