frodo-wii/Src/CPU1541_SC.cpp

/*
 *  CPU1541_SC.cpp - Single-cycle 6502 (1541) emulation
 *
 *  Frodo (C) 1994-1997,2002-2005 Christian Bauer
 *
 *  This program is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation; either version 2 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, write to the Free Software
 *  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */

/*
 * Notes:
 * ------
 *
 * Opcode execution:
 *  - All opcodes are resolved into single clock cycles. There is one
 *    switch case for each cycle.
 *  - The "state" variable specifies the routine to be executed in the
 *    next cycle. Its upper 8 bits contain the current opcode, its lower
 *    8 bits contain the cycle number (0..7) within the opcode.
 *  - Opcodes are fetched in cycle 0 (state = 0)
 *  - The states 0x0010..0x0027 are used for interrupts
 *  - There is exactly one memory access in each clock cycle
 *
 * Memory map (1541C, the 1541 and 1541-II are a bit different):
 *
 * $0000-$07ff RAM (2K)
 * $0800-$0fff RAM mirror
 * $1000-$17ff free
 * $1800-$1bff VIA 1
 * $1c00-$1fff VIA 2
 * $2000-$bfff free
 * $c000-$ffff ROM (16K)
 *
 *  - All memory accesses are done with the read_byte() and
 *    write_byte() functions which also do the memory address
 *    decoding.
 *  - The possible interrupt sources are:
 *      INT_VIA1IRQ: I flag is checked, jump to ($fffe) (unused)
 *      INT_VIA2IRQ: I flag is checked, jump to ($fffe) (unused)
 *      INT_IECIRQ: I flag is checked, jump to ($fffe) (unused)
 *      INT_RESET: Jump to ($fffc)
 *  - The z_flag variable has the inverse meaning of the
 *    6502 Z flag
 *  - Only the highest bit of the n_flag variable is used
 *  - The $f2 opcode that would normally crash the 6502 is
 *    used to implement emulator-specific functions
 *  - The 1541 6502 emulation also includes a very simple VIA
 *    emulation (enough to make the IEC bus and GCR loading work).
 *    It's too small to move it to a source file of its own.
 *
 * Incompatibilities:
 * ------------------
 *
 *  - VIA emulation incomplete
 */

#include "sysdeps.h"

#include "CPU1541.h"
#include "CPU_common.h"
#include "1541job.h"
#include "C64.h"
#include "CIA.h"
#include "Display.h"


enum {
	INT_RESET = 3
};


/*
 *  6502 constructor: Initialize registers
 */

MOS6502_1541::MOS6502_1541(C64 *c64, Job1541 *job, C64Display *disp, uint8 *Ram, uint8 *Rom)
 : ram(Ram), rom(Rom), the_c64(c64), the_display(disp), the_job(job)
{
	a = x = y = 0;
	sp = 0xff;
	n_flag = z_flag = 0;
	v_flag = d_flag = c_flag = false;
	i_flag = true;

	via1_t1c = via1_t1l = via1_t2c = via1_t2l = 0;
	via1_sr = 0;
	via2_t1c = via2_t1l = via2_t2c = via2_t2l = 0;
	via2_sr = 0;

	first_irq_cycle = 0;
	Idle = false;
}


/*
 *  Reset CPU asynchronously
 */

void MOS6502_1541::AsyncReset(void)
{
	interrupt.intr[INT_RESET] = true;
	Idle = false;
}


/*
 *  Get 6502 register state
 */

void MOS6502_1541::GetState(MOS6502State *s)
{
	s->a = a;
	s->x = x;
	s->y = y;

	s->p = 0x20 | (n_flag & 0x80);
	if (v_flag) s->p |= 0x40;
	if (d_flag) s->p |= 0x08;
	if (i_flag) s->p |= 0x04;
	if (!z_flag) s->p |= 0x02;
	if (c_flag) s->p |= 0x01;
	
	s->pc = pc;
	s->sp = sp | 0x0100;

	s->intr[INT_VIA1IRQ] = interrupt.intr[INT_VIA1IRQ];
	s->intr[INT_VIA2IRQ] = interrupt.intr[INT_VIA2IRQ];
	s->intr[INT_IECIRQ] = interrupt.intr[INT_IECIRQ];
	s->intr[INT_RESET] = interrupt.intr[INT_RESET];
	s->idle = Idle;

	s->via1_pra = via1_pra; s->via1_ddra = via1_ddra;
	s->via1_prb = via1_prb; s->via1_ddrb = via1_ddrb;
	s->via1_t1c = via1_t1c; s->via1_t1l = via1_t1l;
	s->via1_t2c = via1_t2c; s->via1_t2l = via1_t2l;
	s->via1_sr = via1_sr;
	s->via1_acr = via1_acr; s->via1_pcr = via1_pcr;
	s->via1_ifr = via1_ifr; s->via1_ier = via1_ier;

	s->via2_pra = via2_pra; s->via2_ddra = via2_ddra;
	s->via2_prb = via2_prb; s->via2_ddrb = via2_ddrb;
	s->via2_t1c = via2_t1c; s->via2_t1l = via2_t1l;
	s->via2_t2c = via2_t2c; s->via2_t2l = via2_t2l;
	s->via2_sr = via2_sr;
	s->via2_acr = via2_acr; s->via2_pcr = via2_pcr;
	s->via2_ifr = via2_ifr; s->via2_ier = via2_ier;
}


/*
 *  Restore 6502 state
 */

void MOS6502_1541::SetState(MOS6502State *s)
{
	a = s->a;
	x = s->x;
	y = s->y;

	n_flag = s->p;
	v_flag = s->p & 0x40;
	d_flag = s->p & 0x08;
	i_flag = s->p & 0x04;
	z_flag = !(s->p & 0x02);
	c_flag = s->p & 0x01;

	pc = s->pc;
	sp = s->sp & 0xff;

	interrupt.intr[INT_VIA1IRQ] = s->intr[INT_VIA1IRQ];
	interrupt.intr[INT_VIA2IRQ] = s->intr[INT_VIA2IRQ];
	interrupt.intr[INT_IECIRQ] = s->intr[INT_IECIRQ];
	interrupt.intr[INT_RESET] = s->intr[INT_RESET];
	Idle = s->idle;

	via1_pra = s->via1_pra; via1_ddra = s->via1_ddra;
	via1_prb = s->via1_prb; via1_ddrb = s->via1_ddrb;
	via1_t1c = s->via1_t1c; via1_t1l = s->via1_t1l;
	via1_t2c = s->via1_t2c; via1_t2l = s->via1_t2l;
	via1_sr = s->via1_sr;
	via1_acr = s->via1_acr; via1_pcr = s->via1_pcr;
	via1_ifr = s->via1_ifr; via1_ier = s->via1_ier;

	via2_pra = s->via2_pra; via2_ddra = s->via2_ddra;
	via2_prb = s->via2_prb; via2_ddrb = s->via2_ddrb;
	via2_t1c = s->via2_t1c; via2_t1l = s->via2_t1l;
	via2_t2c = s->via2_t2c; via2_t2l = s->via2_t2l;
	via2_sr = s->via2_sr;
	via2_acr = s->via2_acr; via2_pcr = s->via2_pcr;
	via2_ifr = s->via2_ifr; via2_ier = s->via2_ier;
}


/*
 *  Read a byte from I/O space
 */

inline uint8 MOS6502_1541::read_byte_io(uint16 adr)
{
	if ((adr & 0xfc00) == 0x1800)	// VIA 1
		switch (adr & 0xf) {
			case 0:
				return ((via1_prb & 0x1a)
					| ((IECLines & TheCIA2->IECLines) >> 7)			// DATA
					| (((IECLines & TheCIA2->IECLines) >> 4) & 0x04)	// CLK
					| (((TheCIA2->IECLines << 3) & 0x80))) ^ 0x85;		// ATN
			case 1:
			case 15:
				return 0xff;	// Keep 1541C ROMs happy (track 0 sensor)
			case 2:
				return via1_ddrb;
			case 3:
				return via1_ddra;
			case 4:
				via1_ifr &= 0xbf;
				return via1_t1c;
			case 5:
				return via1_t1c >> 8;
			case 6:
				return via1_t1l;
			case 7:
				return via1_t1l >> 8;
			case 8:
				via1_ifr &= 0xdf;
				return via1_t2c;
			case 9:
				return via1_t2c >> 8;
			case 10:
				return via1_sr;
			case 11:
				return via1_acr;
			case 12:
				return via1_pcr;
			case 13:
				return via1_ifr | (via1_ifr & via1_ier ? 0x80 : 0);
			case 14:
				return via1_ier | 0x80;
			default:	// Can't happen
				return 0;
		}

	else if ((adr & 0xfc00) == 0x1c00)	// VIA 2
		switch (adr & 0xf) {
			case 0:
				if (the_job->SyncFound())
					return (via2_prb & 0x7f) | the_job->WPState();
				else
					return (via2_prb | 0x80) | the_job->WPState();
			case 1:
			case 15:
				return the_job->ReadGCRByte();
			case 2:
				return via2_ddrb;
			case 3:
				return via2_ddra;
			case 4:
				via2_ifr &= 0xbf;
				interrupt.intr[INT_VIA2IRQ] = false;	// Clear job IRQ
				return via2_t1c;
			case 5:
				return via2_t1c >> 8;
			case 6:
				return via2_t1l;
			case 7:
				return via2_t1l >> 8;
			case 8:
				via2_ifr &= 0xdf;
				return via2_t2c;
			case 9:
				return via2_t2c >> 8;
			case 10:
				return via2_sr;
			case 11:
				return via2_acr;
			case 12:
				return via2_pcr;
			case 13:
				return via2_ifr | (via2_ifr & via2_ier ? 0x80 : 0);
			case 14:
				return via2_ier | 0x80;
			default:	// Can't happen
				return 0;
		}

	else
		return adr >> 8;
}


/*
 *  Read a byte from the CPU's address space
 */

uint8 MOS6502_1541::read_byte(uint16 adr)
{
	if (adr >= 0xc000)
		return rom[adr & 0x3fff];
	else if (adr < 0x1000)
		return ram[adr & 0x07ff];
	else
		return read_byte_io(adr);
}


/*
 *  Read a word (little-endian) from the CPU's address space
 */

inline uint16 MOS6502_1541::read_word(uint16 adr)
{
	return read_byte(adr) | (read_byte(adr+1) << 8);
}


/*
 *  Write a byte to I/O space
 */

void MOS6502_1541::write_byte_io(uint16 adr, uint8 byte)
{
	if ((adr & 0xfc00) == 0x1800)		// VIA 1
		switch (adr & 0xf) {
			case 0:
				via1_prb = byte;
				byte = ~via1_prb & via1_ddrb;
				IECLines = ((byte << 6) & ((~byte ^ TheCIA2->IECLines) << 3) & 0x80)
					| ((byte << 3) & 0x40);
				break;
			case 1:
			case 15:
				via1_pra = byte;
				break;
			case 2:
				via1_ddrb = byte;
				byte &= ~via1_prb;
				IECLines = ((byte << 6) & ((~byte ^ TheCIA2->IECLines) << 3) & 0x80)
					| ((byte << 3) & 0x40);
				break;
			case 3:
				via1_ddra = byte;
				break;
			case 4:
			case 6:
				via1_t1l = (via1_t1l & 0xff00) | byte;
				break;
			case 5:
				via1_t1l = (via1_t1l & 0xff) | (byte << 8);
				via1_ifr &= 0xbf;
				via1_t1c = via1_t1l;
				break;
			case 7:
				via1_t1l = (via1_t1l & 0xff) | (byte << 8);
				break;
			case 8:
				via1_t2l = (via1_t2l & 0xff00) | byte;
				break;
			case 9:
				via1_t2l = (via1_t2l & 0xff) | (byte << 8);
				via1_ifr &= 0xdf;
				via1_t2c = via1_t2l;
				break;
			case 10:
				via1_sr = byte;
				break;
			case 11:
				via1_acr = byte;
				break;
			case 12:
				via1_pcr = byte;
				break;
			case 13:
				via1_ifr &= ~byte;
				break;
			case 14:
				if (byte & 0x80)
					via1_ier |= byte & 0x7f;
				else
					via1_ier &= ~byte;
				break;
		}

	else if ((adr & 0xfc00) == 0x1c00)
		switch (adr & 0xf) {
			case 0:
				if ((via2_prb ^ byte) & 8)	// Bit 3: Drive LED
					the_display->UpdateLEDs(byte & 8 ? 1 : 0, 0, 0, 0);
				if ((via2_prb ^ byte) & 3)	// Bits 0/1: Stepper motor
				{
					if ((via2_prb & 3) == ((byte+1) & 3))
						the_job->MoveHeadOut();
					else if ((via2_prb & 3) == ((byte-1) & 3))
						the_job->MoveHeadIn();
				}
				via2_prb = byte & 0xef;
				break;
			case 1:
			case 15:
				via2_pra = byte;
				break;
			case 2:
				via2_ddrb = byte;
				break;
			case 3:
				via2_ddra = byte;
				break;
			case 4:
			case 6:
				via2_t1l = (via2_t1l & 0xff00) | byte;
				break;
			case 5:
				via2_t1l = (via2_t1l & 0xff) | (byte << 8);
				via2_ifr &= 0xbf;
				via2_t1c = via2_t1l;
				break;
			case 7:
				via2_t1l = (via2_t1l & 0xff) | (byte << 8);
				break;
			case 8:
				via2_t2l = (via2_t2l & 0xff00) | byte;
				break;
			case 9:
				via2_t2l = (via2_t2l & 0xff) | (byte << 8);
				via2_ifr &= 0xdf;
				via2_t2c = via2_t2l;
				break;
			case 10:
				via2_sr = byte;
				break;
			case 11:
				via2_acr = byte;
				break;
			case 12:
				via2_pcr = byte;
				break;
			case 13:
				via2_ifr &= ~byte;
				break;
			case 14:
				if (byte & 0x80)
					via2_ier |= byte & 0x7f;
				else
					via2_ier &= ~byte;
				break;
		}
}


/*
 *  Write a byte to the CPU's address space
 */

inline void MOS6502_1541::write_byte(uint16 adr, uint8 byte)
{
	if (adr < 0x1000)
		ram[adr & 0x7ff] = byte;
	else
		write_byte_io(adr, byte);
}


/*
 *  Read byte from 6502/1541 address space (used by SAM)
 */

uint8 MOS6502_1541::ExtReadByte(uint16 adr)
{
	return read_byte(adr);
}


/*
 *  Write byte to 6502/1541 address space (used by SAM)
 */

void MOS6502_1541::ExtWriteByte(uint16 adr, uint8 byte)
{
	write_byte(adr, byte);
}


/*
 *  Adc instruction
 */

inline void MOS6502_1541::do_adc(uint8 byte)
{
	if (!d_flag) {
		uint16 tmp;

		// Binary mode
		tmp = a + byte + (c_flag ? 1 : 0);
		c_flag = tmp > 0xff;
		v_flag = !((a ^ byte) & 0x80) && ((a ^ tmp) & 0x80);
		z_flag = n_flag = a = tmp;

	} else {
		uint16 al, ah;

		// Decimal mode
		al = (a & 0x0f) + (byte & 0x0f) + (c_flag ? 1 : 0);		// Calculate lower nybble
		if (al > 9) al += 6;									// BCD fixup for lower nybble

		ah = (a >> 4) + (byte >> 4);							// Calculate upper nybble
		if (al > 0x0f) ah++;

		z_flag = a + byte + (c_flag ? 1 : 0);					// Set flags
		n_flag = ah << 4;	// Only highest bit used
		v_flag = (((ah << 4) ^ a) & 0x80) && !((a ^ byte) & 0x80);

		if (ah > 9) ah += 6;									// BCD fixup for upper nybble
		c_flag = ah > 0x0f;										// Set carry flag
		a = (ah << 4) | (al & 0x0f);							// Compose result
	}
}


/*
 * Sbc instruction
 */

inline void MOS6502_1541::do_sbc(uint8 byte)
{
	uint16 tmp = a - byte - (c_flag ? 0 : 1);

	if (!d_flag) {

		// Binary mode
		c_flag = tmp < 0x100;
		v_flag = ((a ^ tmp) & 0x80) && ((a ^ byte) & 0x80);
		z_flag = n_flag = a = tmp;

	} else {
		uint16 al, ah;

		// Decimal mode
		al = (a & 0x0f) - (byte & 0x0f) - (c_flag ? 0 : 1);		// Calculate lower nybble
		ah = (a >> 4) - (byte >> 4);							// Calculate upper nybble
		if (al & 0x10) {
			al -= 6;											// BCD fixup for lower nybble
			ah--;
		}
		if (ah & 0x10) ah -= 6;									// BCD fixup for upper nybble

		c_flag = tmp < 0x100;									// Set flags
		v_flag = ((a ^ tmp) & 0x80) && ((a ^ byte) & 0x80);
		z_flag = n_flag = tmp;

		a = (ah << 4) | (al & 0x0f);							// Compose result
	}
}


/*
 *  Reset CPU
 */

void MOS6502_1541::Reset(void)
{
	// IEC lines and VIA registers
	IECLines = 0xc0;

	via1_pra = via1_ddra = via1_prb = via1_ddrb = 0;
	via1_acr = via1_pcr = 0;
	via1_ifr = via1_ier = 0;
	via2_pra = via2_ddra = via2_prb = via2_ddrb = 0;
	via2_acr = via2_pcr = 0;
	via2_ifr = via2_ier = 0;

	// Clear all interrupt lines
	interrupt.intr_any = 0;

	// Read reset vector
	pc = read_word(0xfffc);
	state = 0;

	// Wake up 1541
	Idle = false;
}


/*
 *  Illegal opcode encountered
 */

void MOS6502_1541::illegal_op(uint8 op, uint16 at)
{
	char illop_msg[80];

	sprintf(illop_msg, "1541: Illegal opcode %02x at %04x.", op, at);
	if (ShowRequester(illop_msg, "Reset 1541", "Reset C64"))
		the_c64->Reset();
	Reset();
}


/*
 *  Emulate one 6502 clock cycle
 */

// Read byte from memory
#define read_to(adr, to) \
	to = read_byte(adr);

// Read byte from memory, throw away result
#define read_idle(adr) \
	read_byte(adr);

void MOS6502_1541::EmulateCycle(void)
{
	uint8 data, tmp;

	// Any pending interrupts in state 0 (opcode fetch)?
	if (!state && interrupt.intr_any) {
		if (interrupt.intr[INT_RESET])
			Reset();
		else if ((interrupt.intr[INT_VIA1IRQ] || interrupt.intr[INT_VIA2IRQ] || interrupt.intr[INT_IECIRQ]) && (the_c64->CycleCounter-first_irq_cycle >= 2) && !i_flag)
			state = 0x0008;
	}

#define IS_CPU_1541
#include "CPU_emulcycle.h"

		// Extension opcode
		case O_EXT:
			if (pc < 0xc000) {
				illegal_op(0xf2, pc-1);
				break;
			}
			switch (read_byte(pc++)) {
				case 0x00:	// Go to sleep in DOS idle loop if error flag is clear and no command received
					Idle = !(ram[0x26c] | ram[0x7c]);
					pc = 0xebff;
					Last;
				case 0x01:	// Write sector
					the_job->WriteSector();
					pc = 0xf5dc;
					Last;
				case 0x02:	// Format track
					the_job->FormatTrack();
					pc = 0xfd8b;
					Last;
				default:
					illegal_op(0xf2, pc-1);
					break;
			}
			break;

		default:
			illegal_op(op, pc-1);
			break;
	}
}