rockbox/apps/plugins/chip8.c

/***************************************************************************
 *             __________               __   ___.
 *   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 */
#ifndef SIMULATOR
#ifdef HAVE_LCD_BITMAP 

static struct plugin_api* rb; /* here is a global api struct pointer */
unsigned char lcd_framebuf[8][64]; /* frame buffer in hardware fomat */

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            */
};

static struct chip8_regs_struct chip8_regs;

#define chip8_iperiod 10                        /* number of opcodes per    */
                                                /* timeslice (1/50sec.)     */
static byte chip8_key_pressed;
static byte chip8_keys[16];                     /* if 1, key is held down   */
static byte chip8_display[64*32];               /* 0xff if pixel is set,    */
                                                /* 0x00 otherwise           */
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_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);

/****************************************************************************/
/* Turn sound on                                                            */
/****************************************************************************/
static void chip8_sound_on (void) { }

/****************************************************************************/
/* Turn sound off                                                           */
/****************************************************************************/
static void chip8_sound_off (void) { }

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;
}

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

static void op_key (word opcode)
{
 byte key_value,cp_value;
 if ((opcode&0xff)==0x9e)
  cp_value=1;
 else if ((opcode&0xff)==0xa1)
  cp_value=0;
 else
  return;
 key_value=chip8_keys[get_reg_value(opcode)&0x0f];
 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)=rb->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;
}

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;
}

static void op_system (word opcode)
{
 switch ((byte)opcode)
 {
  case 0xe0:
   rb->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;
 }
}

static void op_misc (word opcode)
{
 byte *reg,i,j;
 reg=get_reg_offset(opcode);
 switch ((byte)opcode)
 {
  case 0x07:
   *reg=chip8_regs.delay;
   break;
  case 0x0a:
   if (chip8_key_pressed)
    *reg=chip8_key_pressed-1;
   else
    chip8_regs.pc-=2;
   break;
  case 0x15:
   chip8_regs.delay=*reg;
   break;
  case 0x18:
   chip8_regs.sound=*reg;
   if (chip8_regs.sound) chip8_sound_on();
   break;
  case 0x1e:
   chip8_regs.i+=(*reg);
   break;
  case 0x29:
   chip8_regs.i=((word)(*reg&0x0f))*5;
   break;
  case 0x33:
   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:
   for (i=0,j=(opcode>>8)&0x0f;i<=j;++i)
    write_mem(chip8_regs.i+i,chip8_regs.alg[i]);
   break;
  case 0x65:
   for (i=0,j=(opcode>>8)&0x0f;i<=j;++i)
    chip8_regs.alg[i]=read_mem(chip8_regs.i+i);
   break;
 }
}

static void op_sprite (word opcode)
{
 byte *q;
 byte n,x,x2,y,collision;
 word p;
 x=get_reg_value(opcode)&63;
 y=get_reg_value_2(opcode)&31;
 p=chip8_regs.i;
 q=chip8_display+y*64;
 n=opcode&0x0f;
 if (n+y>32) n=32-y;
 for (collision=1;n;--n,q+=64)
 {
  for (y=read_mem(p++),x2=x;y;y<<=1,x2=(x2+1)&63)
   if (y&0x80) collision&=(q[x2]^=0xff);
 }
 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
};

/****************************************************************************/
/* Update the display                                                       */
/****************************************************************************/
static void chip8_update_display(void)
{
 int x,y,i;
 byte w;
 byte* row;

 for (y=0;y<=7;++y)                             /* 32 rows                  */
 {
  row = lcd_framebuf[y];
  for (x=0;x<64;++x)                            /* 64 columns               */
  {
    w = 0;
    for (i=0;i<=3;i++)
    {
      w = w >> 2;
      if (chip8_display[x+(y*4+i)*64] != 0)
      {
        w += 128+64;
      }
    }
    *row++ = w;
  }
 }
 rb->lcd_blit(lcd_framebuf[0], 24, 0, 64, 8, 64);
}


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

    case BUTTON_UP:                 chip8_keys[2] = 1; break;
    case BUTTON_UP | BUTTON_REL:    chip8_keys[2] = 0; break;
    case BUTTON_LEFT:               chip8_keys[4] = 1; break;
    case BUTTON_LEFT | BUTTON_REL:  chip8_keys[4] = 0; break;
    case BUTTON_RIGHT:              chip8_keys[6] = 1; break;
    case BUTTON_RIGHT | BUTTON_REL: chip8_keys[6] = 0; break;
    case BUTTON_DOWN:               chip8_keys[8] = 1; break;
    case BUTTON_DOWN | BUTTON_REL:  chip8_keys[8] = 0; break;
    case BUTTON_PLAY:               chip8_keys[5] = 1; break;
    case BUTTON_PLAY | BUTTON_REL:  chip8_keys[5] = 0; break;
    case BUTTON_F1:                 chip8_keys[1] = 1; break;
    case BUTTON_F1 | BUTTON_REL:    chip8_keys[1] = 0; break;
    case BUTTON_F2:                 chip8_keys[7] = 1; break;
    case BUTTON_F2 | BUTTON_REL:    chip8_keys[7] = 0; break;
    case BUTTON_F3:                 chip8_keys[3] = 1; break;
    case BUTTON_F3 | BUTTON_REL:    chip8_keys[3] = 0; break;
    case BUTTON_ON:                 chip8_keys[9] = 1; break;
    case BUTTON_ON | BUTTON_REL:    chip8_keys[9] = 0; break;

    case SYS_USB_CONNECTED:
#ifdef HAVE_LCD_CHARCELLS
      status_set_param(false);
#endif
      chip8_running = false;
      break;
  }
}


/****************************************************************************/
/* 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);

    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) --chip8_regs.sound; /* How could we make sound on the archos? */
                                               /* Update the machine status */
  chip8_update_display();
  chip8_keyboard();
  rb->yield();  /* we should regulate the speed by timer query, sleep/yield */

  for (i=key_pressed=0;i<16;++i)                /* check if a key was first */
    if (chip8_keys[i]) key_pressed=i+1;         /* pressed                  */
  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[16*5]=
 {
  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,
 };
 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);
 }
 rb->memset (chip8_regs.alg,0,sizeof(chip8_regs.alg));
 rb->memset (chip8_keys,0,sizeof(chip8_keys));
 chip8_key_pressed=0;
 rb->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;
}

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

    fd = rb->open(file, O_RDONLY);
    if (fd==-1) return false;
    numread = rb->read(fd, chip8_mem+0x200, 4096-0x200);
    if (numread==-1) return false;

    rb->close(fd);
    return true;
}

bool chip8_run(char* file)
{
    int ok;

    ok = chip8_init(file);
    if (!ok) {
        rb->lcd_clear_display();
        rb->lcd_puts(0, 0, "Error");
        rb->lcd_update();
        rb->sleep(HZ);
        return false;
    }
    rb->lcd_clear_display();
    rb->lcd_puts(0, 0, "Chip8 Emulator ");
    rb->lcd_puts(0, 1, "    (c) by     ");
    rb->lcd_puts(0, 2, "Marcel de Kogel");
    rb->lcd_puts(0, 3, "    Archos:    ");
    rb->lcd_puts(0, 4, "   Blueloop    ");
    rb->lcd_puts(0, 5, "---------------");
    rb->lcd_puts(0, 6, "File OK...");
    rb->lcd_update();
    rb->sleep(HZ*1);
    rb->lcd_clear_display();
    rb->lcd_drawrect(23,0,66,64);
    rb->lcd_update();
    chip8_reset();
    while (chip8_running) chip8_execute();

    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->lcd_puts(0, 0, "Play .ch8 file!");
        rb->lcd_update();
        rb->sleep(HZ);
        return PLUGIN_ERROR;
    }
    else
    {
        filename = (char*) parameter; 
    }

    /* now go ahead and have fun! */
    return chip8_run(filename) ? PLUGIN_OK : PLUGIN_ERROR;
}

#endif // #ifdef HAVE_LCD_BITMAP 
#endif // #ifndef SIMULATOR