src/cpu/fake6502.c at main · doomsdayone/enhanced-x16-emulator

◆ main enhanced-x16-emulator / src / cpu / fake6502.c

11.4 KiB · C · last changed chore(): initial commit 25 days ago source blame history raw

/* Fake6502 CPU emulator core v1.1 *******************
 * (c)2011 Mike Chambers ([email protected])       *
 *****************************************************
 * v1.1 - Small bugfix in BIT opcode, but it was the *
 *        difference between a few games in my NES   *
 *        emulator working and being broken!         *
 *        I went through the rest carefully again    *
 *        after fixing it just to make sure I didn't *
 *        have any other typos! (Dec. 17, 2011)      *
 *                                                   *
 * v1.0 - First release (Nov. 24, 2011)              *
 *****************************************************
 * LICENSE: This source code is released into the    *
 * public domain, but if you use it please do give   *
 * credit. I put a lot of effort into writing this!  *
 *                                                   *
 *****************************************************
 * Fake6502 is a MOS Technology 6502 CPU emulation   *
 * engine in C. It was written as part of a Nintendo *
 * Entertainment System emulator I've been writing.  *
 *                                                   *
 * If you do discover an error in timing accuracy,   *
 * or operation in general please e-mail me at the   *
 * address above so that I can fix it. Thank you!    *
 *                                                   *
 *****************************************************
 * Usage:                                            *
 *                                                   *
 * Fake6502 requires you to provide two external     *
 * functions:                                        *
 *                                                   *
 * uint8_t read6502(uint16_t address, uint8_t bank)  *
 * void write6502(uint16_t address, uint8_t bank,    *
 * uint8_t value)                                    *
 *                                                   *
 * You may optionally pass Fake6502 the pointer to a *
 * function which you want to be called after every  *
 * emulated instruction. This function should be a   *
 * void with no parameters expected to be passed to  *
 * it.                                               *
 *                                                   *
 * This can be very useful. For example, in a NES    *
 * emulator, you check the number of clock ticks     *
 * that have passed so you can know when to handle   *
 * APU events.                                       *
 *                                                   *
 * To pass Fake6502 this pointer, use the            *
 * hookexternal(void *funcptr) function provided.    *
 *                                                   *
 * To disable the hook later, pass NULL to it.       *
 *****************************************************
 * Useful functions in this emulator:                *
 *                                                   *
 * void reset6502(bool c816)                         *
 *   - Call this once before you begin execution.    *
 *                                                   *
 * void exec6502(uint32_t tickcount)                 *
 *   - Execute 6502 code up to the next specified    *
 *     count of clock ticks.                         *
 *                                                   *
 * void step6502()                                   *
 *   - Execute a single instrution.                  *
 *                                                   *
 * void irq6502()                                    *
 *   - Trigger a hardware IRQ in the 6502 core.      *
 *                                                   *
 * void nmi6502()                                    *
 *   - Trigger an NMI in the 6502 core.              *
 *                                                   *
 * void hookexternal(void *funcptr)                  *
 *   - Pass a pointer to a void function taking no   *
 *     parameters. This will cause Fake6502 to call  *
 *     that function once after each emulated        *
 *     instruction.                                  *
 *                                                   *
 *****************************************************
 * Useful variables in this emulator:                *
 *                                                   *
 * uint32_t clockticks6502                           *
 *   - A running total of the emulated cycle count.  *
 *                                                   *
 * uint32_t instructions                             *
 *   - A running total of the total emulated         *
 *     instruction count. This is not related to     *
 *     clock cycle timing.                           *
 *                                                   *
 *****************************************************/

#include "fake6502.h"
#include "registers.h"
#include "irq_ctx.h"

#include <stdio.h>
#include <stdint.h>

// getvalue16() below is currently unused but kept for completeness. GCC and
// Clang warn about unused statics under -Wall -Werror; MSVC has no equivalent
// attribute and rejects __attribute__ outright.
#ifdef _MSC_VER
#define MAYBE_UNUSED
#else
#define MAYBE_UNUSED __attribute__((unused))
#endif

// 6502 / 65C816 registers

struct regs regs;

//helper variables
uint32_t instructions = 0; //keep track of total instructions executed
uint32_t clockticks6502 = 0, clockgoal6502 = 0;
uint16_t opcode_addr, oldpc, reladdr, value;
uint32_t ea;
uint32_t result;
uint8_t opcode, oldstatus;

bool warn_rockwell = true;

uint8_t penaltyop, penaltyaddr;
uint8_t penaltym = 0;
uint8_t penaltye = 0;
uint8_t penaltyn = 0;
uint8_t penaltyx = 0;
uint8_t penaltyd = 0;
uint8_t waiting = 0;

// Set by acc() and cleared before each instruction, because the obvious test --
// comparing addrtable[opcode] against acc -- is not reliable. acc() and imp()
// are both empty, and MSVC folds identical functions onto one address, so the
// comparison is true for every implied opcode there and false under GCC.
static bool addressing_is_acc = false;

//externally supplied functions
extern uint8_t read6502(uint16_t address, uint8_t bank);
extern void write6502(uint16_t address, uint8_t bank, uint8_t value);
extern void stop6502(uint16_t address, uint8_t bank);
extern void vp6502();
extern uint8_t memory_get_ram_bank();
extern uint8_t memory_get_rom_bank();

static void (*addrtable_c02[256])();
static void (*addrtable_c816[256])();
static void (*optable_c02[256])();
static void (*optable_c816[256])();

static const uint32_t ticktable_c02[256];
static const uint32_t ticktable_c816[256];

static void (**addrtable)();
static void (**optable)();
static const uint32_t *ticktable;

#include "support.h"
#include "modes.h"

void rockwell_warning(const char *instruction) {
    uint8_t pc_bank;

    if (opcode_addr < 0xa000) {
        pc_bank = 0;
    } else if (opcode_addr < 0xc000) {
        pc_bank = memory_get_ram_bank();
    } else {
        pc_bank = memory_get_rom_bank();
    }

    printf("Warning: encountered Rockwell instruction %s at $%02x:%04x.\n", instruction, pc_bank, opcode_addr);
    printf("\tFuture Commander X16 hardware may ship with a 65C816 CPU,\n");
    printf("\twhich does not support these instructions.\n");
    printf("\tThis will be the only warning given for Rockwell\n");
    printf("\tinstructions until the emulator is relaunched.\n");
    printf("\tPass -rockwell to the command line to suppress this warning.\n\n");

    warn_rockwell = false;
}

static uint8_t wrappedBankByte(uint32_t addr) {
    // The direct page and the stack are relocatable anywhere inside bank zero,
    // by D and by S, but neither can leave it. So the second byte of a 16-bit
    // access wraps within bank zero rather than stepping into bank one.
    if (addrtable[opcode] == zp || addrtable[opcode] == zpx ||
        addrtable[opcode] == zpy || addrtable[opcode] == sr) {
        return 0;
    }
    else {
        return bank_byte(addr+1);
    }
}

static uint16_t getvalue(bool use16Bit) {
    if (addressing_is_acc) {
        return use16Bit ? regs.c : (uint16_t)regs.a;
    } else if (use16Bit) {
        return ((uint16_t)read6502(ea, bank_byte(ea)) | ((uint16_t)read6502(ea+1, wrappedBankByte(ea)) << 8));
    }
    return read6502(ea, bank_byte(ea));
}

static uint16_t MAYBE_UNUSED getvalue16() {
    return((uint16_t)read6502(ea, bank_byte(ea)) | ((uint16_t)read6502(ea+1, wrappedBankByte(ea)) << 8));
}

static void putvalue(uint16_t saveval, bool use16Bit) {
    if (addressing_is_acc) {
        if (use16Bit) {
            regs.c = saveval;
        } else {
            regs.a = (uint8_t)(saveval & 0x00FF);
        }
    } else if (use16Bit) {
        write6502(ea, bank_byte(ea), (saveval & 0x00FF));
        write6502(ea + 1, wrappedBankByte(ea), saveval >> 8);
    } else {
        write6502(ea, bank_byte(ea), (saveval & 0x00FF));
    }
}

#include "instructions.h"
#include "65c02.h"
#include "tables.h"

void nmi6502() {
    interrupt6502(INT_NMI);
    waiting = 0;
}

void irq6502() {
    if (!(regs.status & FLAG_INTERRUPT)) {
        interrupt6502(INT_IRQ);
    }
    waiting = 0;
}

uint8_t callexternal = 0;
void (*loopexternal)();

void exec6502(uint32_t tickcount) {
	if (waiting) {
		clockticks6502 += tickcount;
		clockgoal6502 = clockticks6502;
		return;
    }

    opcode_addr = regs.pc;

    clockgoal6502 += tickcount;

    while (clockticks6502 < clockgoal6502) {
        opcode = read6502(regs.pc++, regs.k);

        cpu_pin_status_flags();

        penaltyop = 0;
        penaltyaddr = 0;
        penaltym = 0;
        penaltye = 0;
        penaltyn = 0;
        penaltyx = 0;
        penaltyd = 0;
        addressing_is_acc = false;

        (*addrtable[opcode])();
        (*optable[opcode])();
        cpu_pin_stack_page();
        clockticks6502 += ticktable[opcode];

        // Keep this in sync with step6502().
        if (penaltyop && penaltyaddr) clockticks6502++;
        if (memory_16bit()) clockticks6502 += penaltym;
        if (index_16bit()) clockticks6502 += penaltyx;
        if (penaltyn && !regs.e) clockticks6502++;
        if (penaltye && regs.e) clockticks6502++;
        if (penaltyd) clockticks6502++;

        instructions++;

        if (callexternal) (*loopexternal)();
    }
}

void step6502() {
	if (waiting) {
		++clockticks6502;
		clockgoal6502 = clockticks6502;
		return;
	}

    opcode_addr = regs.pc;

    opcode = read6502(regs.pc++, regs.k);

    cpu_pin_status_flags();

    penaltyop = 0;
    penaltyaddr = 0;
    penaltym = 0;
    penaltye = 0;
    penaltyn = 0;
    penaltyx = 0;
    // Otherwise this sticks: after one misaligned direct-page access every later
    // instruction costs an extra cycle, and reset6502() doesn't clear it either.
    penaltyd = 0;
        addressing_is_acc = false;

    (*addrtable[opcode])();
    (*optable[opcode])();
    cpu_pin_stack_page();
    clockticks6502 += ticktable[opcode];

    if (penaltyop && penaltyaddr) clockticks6502++;
    if (memory_16bit()) clockticks6502 += penaltym;
    if (index_16bit()) clockticks6502 += penaltyx;
    if (penaltyn && !regs.e) clockticks6502++;
    if (penaltye && regs.e) clockticks6502++;
    if (penaltyd) clockticks6502 ++;
    clockgoal6502 = clockticks6502;

    instructions++;

    if (callexternal) (*loopexternal)();
}

void hookexternal(void *funcptr) {
    if (funcptr != (void *)NULL) {
        loopexternal = funcptr;
        callexternal = 1;
    } else callexternal = 0;
}

//  Fixes from http://6502.org/tutorials/65c02opcodes.html
//
//  65C02 Cycle Count differences.
//        ADC/SBC work differently in decimal mode.
//        The wraparound fixes may not be required.

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9120e874 Andy McCall 25 days ago	1	/* Fake6502 CPU emulator core v1.1 *******************
	2	* (c)2011 Mike Chambers ([email protected]) *
	3	*****************************************************
	4	* v1.1 - Small bugfix in BIT opcode, but it was the *
	5	* difference between a few games in my NES *
	6	* emulator working and being broken! *
	7	* I went through the rest carefully again *
	8	* after fixing it just to make sure I didn't *
	9	* have any other typos! (Dec. 17, 2011) *
	10	* *
	11	* v1.0 - First release (Nov. 24, 2011) *
	12	*****************************************************
	13	* LICENSE: This source code is released into the *
	14	* public domain, but if you use it please do give *
	15	* credit. I put a lot of effort into writing this! *
	16	* *
	17	*****************************************************
	18	* Fake6502 is a MOS Technology 6502 CPU emulation *
	19	* engine in C. It was written as part of a Nintendo *
	20	* Entertainment System emulator I've been writing. *
	21	* *
	22	* If you do discover an error in timing accuracy, *
	23	* or operation in general please e-mail me at the *
	24	* address above so that I can fix it. Thank you! *
	25	* *
	26	*****************************************************
	27	* Usage: *
	28	* *
	29	* Fake6502 requires you to provide two external *
	30	* functions: *
	31	* *
	32	* uint8_t read6502(uint16_t address, uint8_t bank) *
	33	* void write6502(uint16_t address, uint8_t bank, *
	34	* uint8_t value) *
	35	* *
	36	* You may optionally pass Fake6502 the pointer to a *
	37	* function which you want to be called after every *
	38	* emulated instruction. This function should be a *
	39	* void with no parameters expected to be passed to *
	40	* it. *
	41	* *
	42	* This can be very useful. For example, in a NES *
	43	* emulator, you check the number of clock ticks *
	44	* that have passed so you can know when to handle *
	45	* APU events. *
	46	* *
	47	* To pass Fake6502 this pointer, use the *
	48	* hookexternal(void funcptr) function provided.
	49	* *
	50	* To disable the hook later, pass NULL to it. *
	51	*****************************************************
	52	* Useful functions in this emulator: *
	53	* *
	54	* void reset6502(bool c816) *
	55	* - Call this once before you begin execution. *
	56	* *
	57	* void exec6502(uint32_t tickcount) *
	58	* - Execute 6502 code up to the next specified *
	59	* count of clock ticks. *
	60	* *
	61	* void step6502() *
	62	* - Execute a single instrution. *
	63	* *
	64	* void irq6502() *
65	* - Trigger a hardware IRQ in the 6502 core. *
66	* *
67	* void nmi6502() *
68	* - Trigger an NMI in the 6502 core. *
69	* *
70	* void hookexternal(void funcptr)
71	* - Pass a pointer to a void function taking no *
72	* parameters. This will cause Fake6502 to call *
73	* that function once after each emulated *
74	* instruction. *
75	* *
76	*****************************************************
77	* Useful variables in this emulator: *
78	* *
79	* uint32_t clockticks6502 *
80	* - A running total of the emulated cycle count. *
81	* *
82	* uint32_t instructions *
83	* - A running total of the total emulated *
84	* instruction count. This is not related to *
85	* clock cycle timing. *
86	* *
87	*****************************************************/
88
89	#include "fake6502.h"
90	#include "registers.h"
91	#include "irq_ctx.h"
92
93	#include <stdio.h>
94	#include <stdint.h>
95
96	// getvalue16() below is currently unused but kept for completeness. GCC and
97	// Clang warn about unused statics under -Wall -Werror; MSVC has no equivalent
98	// attribute and rejects __attribute__ outright.
99	#ifdef _MSC_VER
100	#define MAYBE_UNUSED
101	#else
102	#define MAYBE_UNUSED __attribute__((unused))
103	#endif
104
105	// 6502 / 65C816 registers
106
107	struct regs regs;
108
109	//helper variables
110	uint32_t instructions = 0; //keep track of total instructions executed
111	uint32_t clockticks6502 = 0, clockgoal6502 = 0;
112	uint16_t opcode_addr, oldpc, reladdr, value;
113	uint32_t ea;
114	uint32_t result;
115	uint8_t opcode, oldstatus;
116
117	bool warn_rockwell = true;
118
119	uint8_t penaltyop, penaltyaddr;
120	uint8_t penaltym = 0;
121	uint8_t penaltye = 0;
122	uint8_t penaltyn = 0;
123	uint8_t penaltyx = 0;
124	uint8_t penaltyd = 0;
125	uint8_t waiting = 0;
126
127	// Set by acc() and cleared before each instruction, because the obvious test --
128	// comparing addrtable[opcode] against acc -- is not reliable. acc() and imp()
129	// are both empty, and MSVC folds identical functions onto one address, so the
130	// comparison is true for every implied opcode there and false under GCC.
131	static bool addressing_is_acc = false;
132
133	//externally supplied functions
134	extern uint8_t read6502(uint16_t address, uint8_t bank);
135	extern void write6502(uint16_t address, uint8_t bank, uint8_t value);
136	extern void stop6502(uint16_t address, uint8_t bank);
137	extern void vp6502();
138	extern uint8_t memory_get_ram_bank();
139	extern uint8_t memory_get_rom_bank();
140
141	static void (*addrtable_c02[256])();
142	static void (*addrtable_c816[256])();
143	static void (*optable_c02[256])();
144	static void (*optable_c816[256])();
145
146	static const uint32_t ticktable_c02[256];
147	static const uint32_t ticktable_c816[256];
148
149	static void (**addrtable)();
150	static void (**optable)();
151	static const uint32_t *ticktable;
152
153	#include "support.h"
154	#include "modes.h"
155
156	void rockwell_warning(const char *instruction) {
157	uint8_t pc_bank;
158
159	if (opcode_addr < 0xa000) {
160	pc_bank = 0;
161	} else if (opcode_addr < 0xc000) {
162	pc_bank = memory_get_ram_bank();
163	} else {
164	pc_bank = memory_get_rom_bank();
165	}
166
167	printf("Warning: encountered Rockwell instruction %s at $%02x:%04x.\n", instruction, pc_bank, opcode_addr);
168	printf("\tFuture Commander X16 hardware may ship with a 65C816 CPU,\n");
169	printf("\twhich does not support these instructions.\n");
170	printf("\tThis will be the only warning given for Rockwell\n");
171	printf("\tinstructions until the emulator is relaunched.\n");
172	printf("\tPass -rockwell to the command line to suppress this warning.\n\n");
173
174	warn_rockwell = false;
175	}
176
177	static uint8_t wrappedBankByte(uint32_t addr) {
178	// The direct page and the stack are relocatable anywhere inside bank zero,
179	// by D and by S, but neither can leave it. So the second byte of a 16-bit
180	// access wraps within bank zero rather than stepping into bank one.
181	if (addrtable[opcode] == zp \|\| addrtable[opcode] == zpx \|\|
182	addrtable[opcode] == zpy \|\| addrtable[opcode] == sr) {
183	return 0;
184	}
185	else {
186	return bank_byte(addr+1);
187	}
188	}
189
190	static uint16_t getvalue(bool use16Bit) {
191	if (addressing_is_acc) {
192	return use16Bit ? regs.c : (uint16_t)regs.a;
193	} else if (use16Bit) {
194	return ((uint16_t)read6502(ea, bank_byte(ea)) \| ((uint16_t)read6502(ea+1, wrappedBankByte(ea)) << 8));
195	}
196	return read6502(ea, bank_byte(ea));
197	}
198
199	static uint16_t MAYBE_UNUSED getvalue16() {
200	return((uint16_t)read6502(ea, bank_byte(ea)) \| ((uint16_t)read6502(ea+1, wrappedBankByte(ea)) << 8));
201	}
202
203	static void putvalue(uint16_t saveval, bool use16Bit) {
204	if (addressing_is_acc) {
205	if (use16Bit) {
206	regs.c = saveval;
207	} else {
208	regs.a = (uint8_t)(saveval & 0x00FF);
209	}
210	} else if (use16Bit) {
211	write6502(ea, bank_byte(ea), (saveval & 0x00FF));
212	write6502(ea + 1, wrappedBankByte(ea), saveval >> 8);
213	} else {
214	write6502(ea, bank_byte(ea), (saveval & 0x00FF));
215	}
216	}
217
218	#include "instructions.h"
219	#include "65c02.h"
220	#include "tables.h"
221
222	void nmi6502() {
223	interrupt6502(INT_NMI);
224	waiting = 0;
225	}
226
227	void irq6502() {
228	if (!(regs.status & FLAG_INTERRUPT)) {
229	interrupt6502(INT_IRQ);
230	}
231	waiting = 0;
232	}
233
234	uint8_t callexternal = 0;
235	void (*loopexternal)();
236
237	void exec6502(uint32_t tickcount) {
238	if (waiting) {
239	clockticks6502 += tickcount;
240	clockgoal6502 = clockticks6502;
241	return;
242	}
243
244	opcode_addr = regs.pc;
245
246	clockgoal6502 += tickcount;
247
248	while (clockticks6502 < clockgoal6502) {
249	opcode = read6502(regs.pc++, regs.k);
250
251	cpu_pin_status_flags();
252
253	penaltyop = 0;
254	penaltyaddr = 0;
255	penaltym = 0;
256	penaltye = 0;
257	penaltyn = 0;
258	penaltyx = 0;
259	penaltyd = 0;
260	addressing_is_acc = false;
261
262	(*addrtable[opcode])();
263	(*optable[opcode])();
264	cpu_pin_stack_page();
265	clockticks6502 += ticktable[opcode];
266
267	// Keep this in sync with step6502().
268	if (penaltyop && penaltyaddr) clockticks6502++;
269	if (memory_16bit()) clockticks6502 += penaltym;
270	if (index_16bit()) clockticks6502 += penaltyx;
271	if (penaltyn && !regs.e) clockticks6502++;
272	if (penaltye && regs.e) clockticks6502++;
273	if (penaltyd) clockticks6502++;
274
275	instructions++;
276
277	if (callexternal) (*loopexternal)();
278	}
279	}
280
281	void step6502() {
282	if (waiting) {
283	++clockticks6502;
284	clockgoal6502 = clockticks6502;
285	return;
286	}
287
288	opcode_addr = regs.pc;
289
290	opcode = read6502(regs.pc++, regs.k);
291
292	cpu_pin_status_flags();
293
294	penaltyop = 0;
295	penaltyaddr = 0;
296	penaltym = 0;
297	penaltye = 0;
298	penaltyn = 0;
299	penaltyx = 0;
300	// Otherwise this sticks: after one misaligned direct-page access every later
301	// instruction costs an extra cycle, and reset6502() doesn't clear it either.
302	penaltyd = 0;
303	addressing_is_acc = false;
304
305	(*addrtable[opcode])();
306	(*optable[opcode])();
307	cpu_pin_stack_page();
308	clockticks6502 += ticktable[opcode];
309
310	if (penaltyop && penaltyaddr) clockticks6502++;
311	if (memory_16bit()) clockticks6502 += penaltym;
312	if (index_16bit()) clockticks6502 += penaltyx;
313	if (penaltyn && !regs.e) clockticks6502++;
314	if (penaltye && regs.e) clockticks6502++;
315	if (penaltyd) clockticks6502 ++;
316	clockgoal6502 = clockticks6502;
317
318	instructions++;
319
320	if (callexternal) (*loopexternal)();
321	}
322
323	void hookexternal(void *funcptr) {
324	if (funcptr != (void *)NULL) {
325	loopexternal = funcptr;
326	callexternal = 1;
327	} else callexternal = 0;
328	}
329
330	// Fixes from http://6502.org/tutorials/65c02opcodes.html
331	//
332	// 65C02 Cycle Count differences.
333	// ADC/SBC work differently in decimal mode.
334	// The wraparound fixes may not be required.

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