path: root/src/czx81.c

/*
    czx81 - ZX81 CURSES emulator
    Copyright (C) 2020 Ian Cowburn

    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
    the Free Software Foundation, either version 3 of the License, or
    (at your option) any later version.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with this program.  If not, see <http://www.gnu.org/licenses/>.
*/
#include "wide_curses.h"

#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <time.h>
#include <locale.h>
#include <string.h>

#include "z80.h"
#include "zx81rom.h"

/* -------------------------------------------------- MACROS
*/
#define ROMLEN		0x2000
#define ROM_SAVE	0x2fc
#define ROM_LOAD	0x347

#define ED_SAVE		0xf0
#define ED_LOAD		0xf1
#define ED_WAITKEY	0xf2
#define ED_ENDWAITKEY	0xf3
#define ED_PAUSE	0xf4

#define SLOW_TSTATES	16000
#define FAST_TSTATES	64000

#define E_LINE		16404
#define LASTK1		16421
#define LASTK2		16422
#define MARGIN		16424
#define FRAMES		16436
#define CDFLAG		16443

#define DFILE		0x400c

#define PEEKW(addr)	(mem[addr] | (Z80Word)mem[addr+1]<<8)

#define POKEW(addr,val)	do						\
			{						\
			    Z80Word wa = addr;				\
			    Z80Word wv = val;				\
			    mem[wa] = wv;				\
			    mem[wa+1] = wv>>8;				\
			} while(0)

#define TXT_W		32
#define TXT_H		24

/* -------------------------------------------------- GLOBALS
*/
static Z80Val		FRAME_TSTATES = FAST_TSTATES;

static Z80Byte		mem[0x10000];

static Z80Word		RAMBOT;
static Z80Word		RAMTOP;

static int		waitkey = FALSE;
static int		started = FALSE;

static unsigned		prev_lk1;
static unsigned		prev_lk2;

static Z80		*z80;

static Z80Byte		matrix[8];

static wchar_t		scrcode[0x40] =
{
	L' ', L'\u2598', L'\u259d', L'\u2580', 		/* 00 - 03 */		
	L'\u2596', L'\u258c', L'\u259e', L'\u259b', 	/* 04 - 07 */		
	L'\u2592', L'\u2584', L'\u2580', L'"', 		/* 08 - 0b */		
	L'\u00a3', L'$', L':', L'?', 			/* 0c - 0f */		
	L'(', L')', L'>', L'<', 			/* 10 - 13 */		
	L'=', L'+', L'-', L'*', 			/* 14 - 17 */		
	L'/', L';', L',', L'.', 			/* 18 - 1b */		
	L'0', L'1', L'2', L'3',				/* 1c - 1f */
	L'4', L'5', L'6', L'7',				/* 20 - 23 */
	L'8', L'9', L'A', L'B',				/* 24 - 27 */
	L'C', L'D', L'E', L'F',				/* 28 - 2b */
	L'G', L'H', L'I', L'J',				/* 2c - 2f */
	L'K', L'L', L'M', L'N',				/* 30 - 33 */
	L'O', L'P', L'Q', L'R',				/* 34 - 37 */
	L'S', L'T', L'U', L'V',				/* 38 - 3b */
	L'W', L'X', L'Y', L'Z',				/* 3c - 3f */
};


/* -------------------------------------------------- ZX81 CODE
*/
static void RomPatch(const Z80Byte patch[], Z80Word addr)
{
    int f;

    for(f = 0; patch[f] != 0xff; f++)
    {
	mem[addr++] = patch[f];
    }
}


static int EDCallback(Z80 *z80, Z80Val data)
{
    Z80Word pause;

    switch((Z80Byte)data)
    {
    	case ED_SAVE:
	    if (z80->DE.w < 0x8000)
	    {
	    	/* TODO: Save */
	    }

	    break;

	case ED_LOAD:
	    if (z80->DE.w < 0x8000)
	    {
	    	/* TODO: Load */
	    }

	    mem[CDFLAG] = 0xc0;

	    break;

	case ED_WAITKEY:
	    waitkey = TRUE;
	    started = TRUE;
	    break;

	case ED_ENDWAITKEY:
	    waitkey = FALSE;
	    break;

	case ED_PAUSE:
	    waitkey = TRUE;

	    pause = z80->BC.w;

	    while(pause-- && !(mem[CDFLAG]&1))
	    {
	    	/* TODO: Pause code */
	    }

	    waitkey = FALSE;
	    break;
    }

    return TRUE;
}


static void ZX81HouseKeeping(void)
{
    unsigned row;
    unsigned lastk1;
    unsigned lastk2;

    /* British ZX81
    */
    mem[MARGIN]=55;

    /* Update FRAMES
    */
    if (FRAME_TSTATES == SLOW_TSTATES)
    {
    	Z80Word frame = PEEKW(FRAMES) & 0x7fff;

	if (frame)
	{
	    frame--;
	}

	POKEW(FRAMES, frame|0x8000);
    }

    if (!started)
    {
    	prev_lk1 = 0;
    	prev_lk2 = 0;
	return;
    }

    /* Update LASTK
    */
    lastk1 = 0;
    lastk2 = 0;

    for(row = 0; row < 8; row++)
    {
    	unsigned b;

	b = (~matrix[row]&0x1f)<<1;

	if (row == 0)
	{
	    unsigned shift;

	    shift = b&2;
	    b &= ~2;
	    b |= (shift>>1);
	}

	if (b)
	{
	    if (b > 1)
	    {
		lastk1 |= (1<<row);
	    }

	    lastk2 |= b;
	}
    }

    if (lastk1 && (lastk1 != prev_lk1 || lastk2 != prev_lk2))
    {
    	mem[CDFLAG] |= 1;
    }
    else
    {
    	mem[CDFLAG] &= ~1;
    }

    mem[LASTK1] = lastk1^0xff;
    mem[LASTK2] = lastk2^0xff;

    prev_lk1 = lastk1;
    prev_lk2 = lastk2;
}


static int CheckTimers(Z80 *z80, Z80Val val)
{
    if (val >= FRAME_TSTATES)
    {
    	Z80ResetCycles(z80, val - FRAME_TSTATES);

	if (started && ((mem[CDFLAG] & 0x80) || waitkey))
	{
	    FRAME_TSTATES = SLOW_TSTATES;
	}
	else
	{
	    FRAME_TSTATES = FAST_TSTATES;
	}

	if (z80->SP < 0x8000)
	{
	    ZX81HouseKeeping();
	}

    	return FALSE;
    }
    else
    {
    	return TRUE;
    }
}


static Z80Byte ZX81ReadMem(Z80 *z80, Z80Word addr)
{
    return mem[addr];
}


static void ZX81WriteMem(Z80 *z80, Z80Word addr, Z80Byte val)
{
    if (addr >= RAMBOT && addr <= RAMTOP)
    {
	mem[addr] = val;
    }
}


static Z80Byte ZX81ReadPort(Z80 *z80, Z80Word port)
{
    Z80Byte b = 0;

    switch(port & 0xff)
    {
	case 0xfe:
	    switch(port & 0xff00)
	    {
	    	case 0xfe00:
		    b = matrix[0];
		    break;
		case 0xfd00:
		    b = matrix[1];
		    break;
		case 0xfb00:
		    b = matrix[2];
		    break;
		case 0xf700:
		    b = matrix[3];
		    break;
		case 0xef00:
		    b = matrix[4];
		    break;
		case 0xdf00:
		    b = matrix[5];
		    break;
		case 0xbf00:
		    b = matrix[6];
		    break;
		case 0x7f00:
		    b = matrix[7];
		    break;
	    }

	    /* Some code expects some of the top bits set.  Whether this is a
	       good idea or not is unsure.
	    */
	    b |= 0x60;

	    break;

    	default:
	    b = 0xff;
	    break;
    }

    return b;
}


void ZX81WritePort(Z80 *z80, Z80Word port, Z80Byte val)
{
}


static void ZX81Init(void)
{
    static const Z80Byte save[]=
    {
	0xed, ED_SAVE,          /* (SAVE)               */
	0xc3, 0x07, 0x02,       /* JP $0207             */
	0xff                    /* End of patch         */
    };

    static const Z80Byte load[]=
    {
	0xed, ED_LOAD,          /* (LOAD)               */
	0xc3, 0x07, 0x02,       /* JP $0207             */
	0xff                    /* End of patch         */
    };

    static const Z80Byte fast_hack[]=
    {
	0xed, ED_WAITKEY,       /* (START KEY WAIT)     */
	0xcb,0x46,              /* L: bit 0,(hl)        */
	0x28,0xfc,              /* jr z,L               */
	0xed, ED_ENDWAITKEY,    /* (END KEY WAIT)       */
	0x00,                   /* nop                  */
	0xff                    /* End of patch         */
    };

    static const Z80Byte kbd_hack[]=
    {
	0x2a,0x25,0x40,         /* ld hl,(LASTK)        */
	0xc9,                   /* ret                  */
	0xff                    /* End of patch         */
    };

    static const Z80Byte pause_hack[]=
    {
	0xed, ED_PAUSE,         /* (PAUSE)              */
	0x00,                   /* nop                  */
	0xff                    /* End of patch         */
    };

    int f;

    /* Load and patch ROM
    */
    memcpy(mem, ZX81ROM, ROMLEN);

    RomPatch(save, ROM_SAVE);
    RomPatch(load, ROM_LOAD);
    RomPatch(fast_hack, 0x4ca);
    RomPatch(kbd_hack, 0x2bb);
    RomPatch(pause_hack, 0xf3a);

    mem[0x21c] = 0x00;
    mem[0x21d] = 0x00;

    mem[0x0079] = 0;
    mem[0x02ec] = 0;

    /* Lodge Z80 callbacks
    */
    Z80LodgeCallback(z80, eZ80_EDHook, EDCallback);
    Z80LodgeCallback(z80, eZ80_Instruction, CheckTimers);

    /* Mirror the ROM
    */
    memcpy(mem + ROMLEN, mem, ROMLEN);

    /* 16K of memory
    */
    RAMBOT = 0x4000;
    RAMTOP = RAMBOT + 0x4000;

    for(f = RAMBOT; f <= RAMTOP; f++)
    {
    	mem[f] = 0;
    }

    /* Keyboard matrix
    */
    for(f = 0; f < 8; f++)
    {
    	matrix[f] = 0x1f;
    }

    /* Fill the upper 32K with RET opcodes for ULA reads
    */
    for(f = 0x8000; f < 0x10000; f++)
    {
    	mem[f] = 0xc9;
    }
}


static void DrawScreen(void)
{
    int fast;
    int x,y;

    fast = (FRAME_TSTATES == FAST_TSTATES);

    if (fast)
    {
    	for(y = 0; y < TXT_H; y++)
	{
	    for(x = 0; x < TXT_W; x++)
	    {
	    	mvprintw(y, x, "%lc", L'\u2592');
	    }
	}
    }
    else
    {
	Z80Byte *scr;

	scr = mem + PEEKW(DFILE);
	y = 0;

	while(y < TXT_H)
	{
	    scr++;
	    x = 0;

	    while(*scr != 118 && x < TXT_W)
	    {
	    	Z80Byte ch = *scr++;

		if (ch & 0x80)
		{
		    attron(A_REVERSE);
		}

		mvprintw(y, x, "%lc", scrcode[ch & 0x3f]);

		if (ch & 0x80)
		{
		    attroff(A_REVERSE);
		}

	    	x++;
	    }

	    y++;
	}
    }
}


/* -------------------------------------------------- UTILS
*/
static long TimeDiff(const struct timespec *start,
		     const struct timespec *end)
{
    long diff;

    diff = (end->tv_nsec - start->tv_nsec) +
    		(end->tv_sec - start->tv_sec) * 1000000000L;

    return diff;
}


/* -------------------------------------------------- MAIN
*/
int main(void)
{
    struct timespec start;
    int quit = FALSE;

    setlocale(LC_ALL, "");

    z80 = Z80Init(ZX81ReadMem,
    		  ZX81WriteMem,
		  ZX81ReadPort,
		  ZX81WritePort,
		  ZX81ReadMem);

    if (!z80)
    {
    	fprintf(stderr, "Failed to initialise the Z80 CPU\n");
	return EXIT_FAILURE;
    }

    ZX81Init();

    initscr();
    raw();
    noecho();
    keypad(stdscr, TRUE);
    nodelay(stdscr, TRUE);

    clock_gettime(CLOCK_MONOTONIC, &start);

    while(!quit)
    {
	struct timespec end;
	struct timespec pause = {0};
	int ch;

	Z80Exec(z80);

	clear();

	DrawScreen();

	ch = getch();

	if (ch == 3)
	{
	    quit = TRUE;
	}

	refresh();

	clock_gettime(CLOCK_MONOTONIC, &end);
	start = end;
	pause.tv_nsec = 20000000 - TimeDiff(&start, &end);

	if (pause.tv_nsec > 0 && FRAME_TSTATES != FAST_TSTATES)
	{
	    nanosleep(&pause, NULL);
	}
    }

    endwin();

    return EXIT_SUCCESS;
}