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aiie/cpu.cpp

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initial commit
2017-02-19 18:46:13 +00:00
#include "cpu.h"
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include "mmu.h"
// To see calls to unimplemented opcodes, define this:
//#define VERBOSE_CPU_ERRORS
// Macros to set negative and zero flags based on param, X, Y, whatever
#define SETNZ { FLAG(F_N, param & 0x80); FLAG(F_Z, !param); }
#define SETNZX { FLAG(F_N, x & 0x80); FLAG(F_Z, !x); }
#define SETNZY { FLAG(F_N, y & 0x80); FLAG(F_Z, !y); }
#define SETNZA { FLAG(F_N, a & 0x80); FLAG(F_Z, !a); }
#define FLAG(bit, condition) { if (condition) {flags |= bit;} else {flags &= ~bit;} }
#define writemem(addr, val) mmu->write(addr, val)
#define readmem(addr) mmu->read(addr)
enum optype {
O_ILLEGAL,
O_ADC,
O_AND,
O_ASL,
O_ASL_ACC,
O_BCC,
O_BCS,
O_BEQ,
O_BIT,
O_BMI,
O_BNE,
O_BPL,
O_BRA,
O_BRK,
O_BVC,
O_BVS,
O_CLC,
O_CLD,
O_CLI,
O_CLV,
O_CMP,
O_CPX,
O_CPY,
O_DEC,
O_DEC_ACC,
O_DEX,
O_DEY,
O_EOR,
O_INC,
O_INC_ACC,
O_INX,
O_INY,
O_JMP,
O_JSR,
O_LDA,
O_LDX,
O_LDY,
O_LSR,
O_LSR_ACC,
O_NOP,
O_ORA,
O_PHA,
O_PHP,
O_PHX,
O_PHY,
O_PLA,
O_PLP,
O_PLX,
O_PLY,
O_ROL,
O_ROL_ACC,
O_ROR,
O_ROR_ACC,
O_RTI,
O_RTS,
O_SBC,
O_SEC,
O_SED,
O_SEI,
O_STA,
O_STX,
O_STY,
O_STZ,
O_TAX,
O_TAY,
O_TRB,
O_TSB,
O_TSX,
O_TXA,
O_TXS,
O_TYA,
// and the "illegal" opcodes (those that don't officially exist for
// the 65c02, but have repeatable results)
O_DCP
};
// accumulator mode is implied
#define A_ACC A_IMP
enum addrmode {
A_ILLEGAL,
A_IMM,
A_ABS,
A_ZER,
A_IMP,
A_REL,
A_ABI,
A_ZEX,
A_ZEY,
A_ZIND,
A_ABX,
A_ABY,
A_INX,
A_INY
};
typedef struct {
optype op;
addrmode mode;
uint8_t cycles;
} optype_t;
optype_t opcodes[256] = {
{ O_BRK, A_IMP, 7 }, // 0x00
{ O_ORA , A_INX , 6 }, // 0x01 [2] i.e. "ORA ($44,X)"
{ O_ILLEGAL, A_ILLEGAL, 2 }, // 0x02
{ O_ILLEGAL, A_ILLEGAL, 2 }, // 0x03
{ O_TSB , A_ZER , 5 }, // 0x04 [2]
{ O_ORA , A_ZER , 3 }, // 0x05 [2] i.e. "ORA $44"
{ O_ASL , A_ZER , 5 }, // 0x06 [2]
{ O_ILLEGAL, A_ILLEGAL, 2 }, // 0x07
{ O_PHP , A_IMP , 3 }, // 0x08
{ O_ORA , A_IMM , 2 }, // 0x09 i.e. "ORA #$44"
{ O_ASL_ACC, A_ACC , 2 }, // 0x0A
{ O_ILLEGAL, A_ILLEGAL, 2 }, // 0x0B
{ O_TSB , A_ABS , 6 }, // 0x0C
{ O_ORA , A_ABS , 4 }, // 0x0D i.e. "ORA $4400"
{ O_ASL , A_ABS , 6 }, // 0x0E
{ O_ILLEGAL, A_ILLEGAL, 2 }, // 0x0F
{ O_BPL , A_REL , 2 }, // 0x10 [8]
{ O_ORA , A_INY , 5 }, // 0x11 [2,3] i.e. "ORA ($44),Y"
{ O_ORA , A_ZIND , 5 }, // 0x12 [2]
{ O_ILLEGAL, A_ILLEGAL, 2 }, // 0x13
{ O_TRB , A_ZER , 5 }, // 0x14 [2]
{ O_ORA , A_ZEX , 4 }, // 0x15 [2] i.e. "ORA $44,X"
{ O_ASL , A_ZEX , 6 }, // 0x16 [2]
{ O_ILLEGAL, A_ILLEGAL, 2 }, // 0x17
{ O_CLC , A_IMP , 2 }, // 0x18
{ O_ORA , A_ABY , 4 }, // 0x19 [3] i.e. "ORA $4400,Y"
{ O_INC_ACC, A_ACC , 2 }, // 0x1A
{ O_ILLEGAL, A_ILLEGAL, 2 }, // 0x1B
{ O_TRB , A_ABS , 6 }, // 0x1C [3]
{ O_ORA , A_ABX , 4 }, // 0x1D [3] i.e. "ORA $4400,X"
{ O_ASL , A_ABX , 6 }, // 0x1E [6]
{ O_ILLEGAL, A_ILLEGAL, 2 }, // 0x1F
{ O_JSR , A_ABS , 6 }, // 0x20
{ O_AND , A_INX , 6 }, // 0x21 [2]
{ O_ILLEGAL, A_ILLEGAL, 2 }, // 0x22
{ O_ILLEGAL, A_ILLEGAL, 2 }, // 0x23
{ O_BIT , A_ZER , 3 }, // 0x24 [2]
{ O_AND , A_ZER , 3 }, // 0x25 [2]
{ O_ROL , A_ZER , 5 }, // 0x26 [2]
{ O_ILLEGAL, A_ILLEGAL, 2 }, // 0x27
{ O_PLP , A_IMP , 4 }, // 0x28
{ O_AND , A_IMM , 2 }, // 0x29
{ O_ROL_ACC, A_ACC , 2 }, // 0x2A
{ O_ILLEGAL, A_ILLEGAL, 2 }, // 0x2B
{ O_BIT , A_ABS , 4 }, // 0x2C
{ O_AND , A_ABS , 4 }, // 0x2D
{ O_ROL , A_ABS , 6 }, // 0x2E
{ O_ILLEGAL, A_ILLEGAL, 2 }, // 0x2F
{ O_BMI , A_REL , 2 }, // 0x30 [8]
{ O_AND , A_INY , 5 }, // 0x31 [2,3]
{ O_AND , A_ZIND , 5 }, // 0x32 [2]
{ O_ILLEGAL, A_ILLEGAL, 2 }, // 0x33
{ O_BIT , A_ZEX , 4 }, // 0x34 [2]
{ O_AND , A_ZEX , 4 }, // 0x35 [2]
{ O_ROL , A_ZEX , 6 }, // 0x36 [2]
{ O_ILLEGAL, A_ILLEGAL, 2 }, // 0x37
{ O_SEC , A_IMP , 2 }, // 0x38
{ O_AND , A_ABY , 4 }, // 0x39 [3]
{ O_DEC_ACC, A_ACC , 2 }, // 0x3A [2]
{ O_ILLEGAL, A_ILLEGAL, 2 }, // 0x3B
{ O_BIT , A_ABX , 4 }, // 0x3C [3]
{ O_AND , A_ABX , 4 }, // 0x3D [3]
{ O_ROL , A_ABX , 6 }, // 0x3E [6]
{ O_ILLEGAL, A_ILLEGAL, 2 }, // 0x3F
{ O_RTI , A_IMP , 6 }, // 0x40
{ O_EOR , A_INX , 6 }, // 0x41 [2]
{ O_ILLEGAL, A_ILLEGAL, 2 }, // 0x42
{ O_ILLEGAL, A_ILLEGAL, 2 }, // 0x43
{ O_ILLEGAL, A_ILLEGAL, 2 }, // 0x44
{ O_EOR , A_ZER , 3 }, // 0x45 [2]
{ O_LSR , A_ZER , 5 }, // 0x46 [2]
{ O_ILLEGAL, A_ILLEGAL, 2 }, // 0x47
{ O_PHA , A_IMP , 3 }, // 0x48
{ O_EOR , A_IMM , 2 }, // 0x49
{ O_LSR_ACC, A_ACC , 2 }, // 0x4A
{ O_ILLEGAL, A_ILLEGAL, 2 }, // 0x4B
{ O_JMP , A_ABS , 3 }, // 0x4C
{ O_EOR , A_ABS , 4 }, // 0x4D
{ O_LSR , A_ABS , 6 }, // 0x4E
{ O_ILLEGAL, A_ILLEGAL, 2 }, // 0x4F
{ O_BVC , A_REL , 2 }, // 0x50 [8]
{ O_EOR , A_INY , 5 }, // 0x51 [2,3]
{ O_EOR , A_ZIND , 5 }, // 0x52
{ O_ILLEGAL, A_ILLEGAL, 2 }, // 0x53
{ O_ILLEGAL, A_ILLEGAL, 2 }, // 0x54
{ O_EOR , A_ZEX , 4 }, // 0x55 [2]
{ O_LSR , A_ZEX , 6 }, // 0x56 [2]
{ O_ILLEGAL, A_ILLEGAL, 2 }, // 0x57
{ O_CLI , A_IMP , 2 }, // 0x58
{ O_EOR , A_ABY , 4 }, // 0x59 [3]
{ O_PHY , A_IMP , 3 }, // 0x5A
{ O_ILLEGAL, A_ILLEGAL, 2 }, // 0x5B
{ O_ILLEGAL, A_ILLEGAL, 2 }, // 0x5C
{ O_EOR , A_ABX , 4 }, // 0x5D [3]
{ O_LSR , A_ABX , 6 }, // 0x5E [6]
{ O_ILLEGAL, A_ILLEGAL, 2 }, // 0x5F
{ O_RTS , A_IMP , 6 }, // 0x60
{ O_ADC , A_INX , 6 }, // 0x61 [2]
{ O_ILLEGAL, A_ILLEGAL, 2 }, // 0x62
{ O_ILLEGAL, A_ILLEGAL, 2 }, // 0x63
{ O_STZ , A_ZER , 3 }, // 0x64 [2]
{ O_ADC , A_ZER , 3 }, // 0x65 [2]
{ O_ROR , A_ZER , 5 }, // 0x66 [2]
{ O_ILLEGAL, A_ILLEGAL, 2 }, // 0x67
{ O_PLA , A_IMP , 4 }, // 0x68
{ O_ADC , A_IMM , 2 }, // 0x69
{ O_ROR_ACC, A_ACC , 2 }, // 0x6A [2]
{ O_ILLEGAL, A_ILLEGAL, 2 }, // 0x6B
{ O_JMP , A_ABI , 6 }, // 0x6C
{ O_ADC , A_ABS , 4 }, // 0x6D
{ O_ROR , A_ABS , 6 }, // 0x6E
{ O_ILLEGAL, A_ILLEGAL, 2 }, // 0x6F
{ O_BVS , A_REL , 2 }, // 0x70 [8]
{ O_ADC , A_INY , 5 }, // 0x71 [2,3]
{ O_ADC , A_ZIND , 5 }, // 0x72 [2]
{ O_ILLEGAL, A_ILLEGAL, 2 }, // 0x73
{ O_STZ , A_ZEX , 4 }, // 0x74 [2]
{ O_ADC , A_ZEX , 4 }, // 0x75 [2]
{ O_ROR , A_ZEX , 6 }, // 0x76 [2]
{ O_ILLEGAL, A_ILLEGAL, 2 }, // 0x77
{ O_SEI , A_IMP , 2 }, // 0x78
{ O_ADC , A_ABY , 4 }, // 0x79 [3]
{ O_PLY , A_IMP , 4 }, // 0x7A
{ O_ILLEGAL, A_ILLEGAL, 2 }, // 0x7B
{ O_JMP , A_ABX , 6 }, // 0x7C
{ O_ADC , A_ABX , 4 }, // 0x7D [3]
{ O_ROR , A_ABX , 6 }, // 0x7E [6]
{ O_ILLEGAL, A_ILLEGAL, 2 }, // 0x7F
{ O_BRA , A_REL , 3 }, // 0x80 [8]
{ O_STA , A_INX , 6 }, // 0x81 [2]
{ O_ILLEGAL, A_ILLEGAL, 2 }, // 0x82
{ O_ILLEGAL, A_ILLEGAL, 2 }, // 0x83
{ O_STY , A_ZER , 3 }, // 0x84 [2]
{ O_STA , A_ZER , 3 }, // 0x85 [2]
{ O_STX , A_ZER , 3 }, // 0x86 [2]
{ O_ILLEGAL, A_ILLEGAL, 2 }, // 0x87
{ O_DEY , A_IMP , 2 }, // 0x88
{ O_BIT , A_IMM , 2 }, // 0x89
{ O_TXA , A_IMP , 2 }, // 0x8A
{ O_ILLEGAL, A_ILLEGAL, 2 }, // 0x8B
{ O_STY , A_ABS , 4 }, // 0x8C
{ O_STA , A_ABS , 4 }, // 0x8D
{ O_STX , A_ABS , 4 }, // 0x8E
{ O_ILLEGAL, A_ILLEGAL, 2 }, // 0x8F
{ O_BCC , A_REL , 2 }, // 0x90 [8]
{ O_STA , A_INY , 6 }, // 0x91 [2]
{ O_STA , A_ZIND , 5 }, // 0x92 [2]
{ O_ILLEGAL, A_ILLEGAL, 2 }, // 0x93
{ O_STY , A_ZEX , 4 }, // 0x94 [2]
{ O_STA , A_ZEX , 4 }, // 0x95 [2]
{ O_STX , A_ZEY , 4 }, // 0x96 [2]
{ O_ILLEGAL, A_ILLEGAL, 2 }, // 0x97
{ O_TYA , A_IMP , 2 }, // 0x98
{ O_STA , A_ABY , 5 }, // 0x99
{ O_TXS , A_IMP , 2 }, // 0x9A [2]
{ O_ILLEGAL, A_ILLEGAL, 2 }, // 0x9B
{ O_STZ , A_ABS , 4 }, // 0x9C
{ O_STA , A_ABX , 5 }, // 0x9D
{ O_STZ , A_ABX , 5 }, // 0x9E
{ O_ILLEGAL, A_ILLEGAL, 2 }, // 0x9F
{ O_LDY , A_IMM , 2 }, // 0xA0
{ O_LDA , A_INX , 6 }, // 0xA1 [2]
{ O_LDX , A_IMM , 2 }, // 0xA2
{ O_ILLEGAL, A_ILLEGAL, 2 }, // 0xA3
{ O_LDY , A_ZER , 3 }, // 0xA4 [2]
{ O_LDA , A_ZER , 3 }, // 0xA5 [2]
{ O_LDX , A_ZER , 3 }, // 0xA6 [2]
{ O_ILLEGAL, A_ILLEGAL, 2 }, // 0xA7
{ O_TAY , A_IMP , 2 }, // 0xA8
{ O_LDA , A_IMM , 2 }, // 0xA9
{ O_TAX , A_IMP , 2 }, // 0xAA
{ O_ILLEGAL, A_ILLEGAL, 2 }, // 0xAB
{ O_LDY , A_ABS , 4 }, // 0xAC
{ O_LDA , A_ABS , 4 }, // 0xAD
{ O_LDX , A_ABS , 4 }, // 0xAE
{ O_ILLEGAL, A_ILLEGAL, 2 }, // 0xAF
{ O_BCS , A_REL , 2 }, // 0xB0 [8]
{ O_LDA , A_INY , 5 }, // 0xB1 [2,3]
{ O_LDA , A_ZIND , 5 }, // 0xB2 [2]
{ O_ILLEGAL, A_ILLEGAL, 2 }, // 0xB3
{ O_LDY , A_ZEX , 4 }, // 0xB4 [2]
{ O_LDA , A_ZEX , 4 }, // 0xB5 [2]
{ O_LDX , A_ZEY , 4 }, // 0xB6 [2]
{ O_ILLEGAL, A_ILLEGAL, 2 }, // 0xB7
{ O_CLV , A_IMP , 2 }, // 0xB8
{ O_LDA , A_ABY , 4 }, // 0xB9 [3]
{ O_TSX , A_IMP , 2 }, // 0xBA
{ O_ILLEGAL, A_ILLEGAL, 2 }, // 0xBB
{ O_LDY , A_ABX , 4 }, // 0xBC [3]
{ O_LDA , A_ABX , 4 }, // 0xBD [3]
{ O_LDX , A_ABY , 4 }, // 0xBE [3]
{ O_ILLEGAL, A_ILLEGAL, 2 }, // 0xBF
{ O_CPY , A_IMM , 2 }, // 0xC0
{ O_CMP , A_INX , 6 }, // 0xC1 [2]
{ O_ILLEGAL, A_ILLEGAL, 2 }, // 0xC2
{ O_DCP, A_INX, 2 }, // 0xC3 -- fixme -- cycle count of this illegal instruction?
{ O_CPY , A_ZER , 3 }, // 0xC4 [2]
{ O_CMP , A_ZER , 3 }, // 0xC5 [2]
{ O_DEC , A_ZER , 5 }, // 0xC6 [2]
{ O_DCP , A_ZER , 2 }, // 0xC7 -- fixme -- cycle count of this illegal instruction?
{ O_INY , A_IMP , 2 }, // 0xC8
{ O_CMP , A_IMM , 2 }, // 0xC9
{ O_DEX , A_IMP , 2 }, // 0xCA
{ O_ILLEGAL, A_ILLEGAL, 2 }, // 0xCB
{ O_CPY , A_ABS , 4 }, // 0xCC
{ O_CMP , A_ABS , 4 }, // 0xCD
{ O_DEC , A_ABS , 6 }, // 0xCE
{ O_DCP , A_ABS , 2 }, // 0xCF -- fixme -- cycle count of this illegal instruction?
{ O_BNE , A_REL , 2 }, // 0xD0 [8]
{ O_CMP , A_INY , 5 }, // 0xD1 [2,3]
{ O_CMP , A_ZIND , 5 }, // 0xD2 [2]
{ O_DCP , A_INY , 2 }, // 0xD3 -- fixme -- cycle count of this illegal instruction?
{ O_ILLEGAL, A_ILLEGAL, 2 }, // 0xD4
{ O_CMP , A_ZEX , 4 }, // 0xD5 [2]
{ O_DEC , A_ZEX , 6 }, // 0xD6 [2]
{ O_DCP , A_ZEX , 2 }, // 0xD7 -- fixme -- cycle count of this illegal instruction?
{ O_CLD , A_IMP , 2 }, // 0xD8
{ O_CMP , A_ABY , 4 }, // 0xD9 [3]
{ O_PHX , A_IMP , 3 }, // 0xDA
{ O_DCP , A_ABY , 2 }, // 0xDB -- fixme -- cycle count of this illegal instruction?
{ O_ILLEGAL, A_ILLEGAL, 2 }, // 0xDC
{ O_CMP , A_ABX , 4 }, // 0xDD [3]
{ O_DEC , A_ABX , 6 }, // 0xDE [6]
{ O_DCP , A_ABX , 2 }, // 0xDF -- fixme -- cycle count of this illegal instruction?
{ O_CPX , A_IMM , 2 }, // 0xE0
{ O_SBC , A_INX , 6 }, // 0xE1 [2]
{ O_ILLEGAL, A_ILLEGAL, 2 }, // 0xE2
{ O_ILLEGAL, A_ILLEGAL, 2 }, // 0xE3
{ O_CPX , A_ZER , 3 }, // 0xE4 [2]
{ O_SBC , A_ZER , 3 }, // 0xE5 [2]
{ O_INC , A_ZER , 5 }, // 0xE6 [2]
{ O_ILLEGAL, A_ILLEGAL, 2 }, // 0xE7
{ O_INX , A_IMP , 2 }, // 0xE8
{ O_SBC , A_IMM , 2 }, // 0xE9
{ O_NOP , A_IMP , 2 }, // 0xEA
{ O_ILLEGAL, A_ILLEGAL, 2 }, // 0xEB
{ O_CPX , A_ABS , 4 }, // 0xEC
{ O_SBC , A_ABS , 4 }, // 0xED
{ O_INC , A_ABS , 6 }, // 0xEE
{ O_ILLEGAL, A_ILLEGAL, 2 }, // 0xEF
{ O_BEQ , A_REL , 2 }, // 0xF0 [8]
{ O_SBC , A_INY , 5 }, // 0xF1 [2,3]
{ O_SBC , A_ZIND , 5 }, // 0xF2 [2]
{ O_ILLEGAL, A_ILLEGAL, 2 }, // 0xF3
{ O_ILLEGAL, A_ILLEGAL, 2 }, // 0xF4
{ O_SBC , A_ZEX , 4 }, // 0xF5 [2]
{ O_INC , A_ZEX , 6 }, // 0xF6 [2]
{ O_ILLEGAL, A_ILLEGAL, 2 }, // 0xF7
{ O_SED , A_IMP , 2 }, // 0xF8
{ O_SBC , A_ABY , 4 }, // 0xF9 [3]
{ O_PLX , A_IMP , 4 }, // 0xFA
{ O_ILLEGAL, A_ILLEGAL, 2 }, // 0xFB
{ O_ILLEGAL, A_ILLEGAL, 2 }, // 0xFC
{ O_SBC , A_ABX , 4 }, // 0xFD [3]
{ O_INC , A_ABX , 6 }, // 0xFE [6]
{ O_ILLEGAL, A_ILLEGAL, 2 }, // 0xFF
};
/* cycle count footnotes:
2: Add 1 cycle if low byte of Direct Page Register is non-zero
3 Add 1 cycle if adding index crosses a page boundary
6 Add 1 cycle if 65C02 and page boundary crossed
8 Add 1 cycle if branch taken crosses page boundary on 6502, 65C02, or 65816's 6502 emulation mode (e=1)
*/
// Initialization sequence comes from http://www.pagetable.com/?p=410
// (the Visual 6502 project).
Cpu::Cpu()
{
mmu = NULL;
Reset();
}
Cpu::~Cpu()
{
mmu = NULL;
}
void Cpu::Reset()
{
a = 0;
x = 0;
y = 0;
flags = F_Z | F_UNK; // FIXME: is that F_UNK flag right here?
if (mmu) {
pc = readmem(0xFFFC) | (readmem(0xFFFD) << 8);
} else {
pc = 0x0000;
}
sp = 0xFD;
cycles = 6; // according to the datasheet, the reset routine takes 6 clock cycles
}
void Cpu::nmi()
{
flags &= ~F_B; // clear break flag
pushS16(pc);
pushS8(flags);
flags |= 0x20; // FIXME: what flag is this?
pc = readmem(0xFFFA) | (readmem(0xFFFB) << 8);
cycles += 2;
}
void Cpu::rst()
{
// On reset, the CPU initializes the instruction register (IR) to 0.
// That's BRK. So we spend 3 cycles breaking (0, 1, 2)?
// Then we would pushS16(pc), but the Reset logic has the R/W line set
// to R, so the value is discarded. Twice. That's cycles 3 and 4.
cycles += 2; sp -= 2;
// Then we would pushS8(flags) the status register, but again, R/W
// is still R. That's cycle 5.
cycles++; sp--;
// Note that in the real CPU, the SP register doesn't get updated
// until now - pushS16/pushS8 wouldn't have updated it. Not sure
// that's ever important to me.
// In cycle 6, we read 0xFFFC; in cycle 7, we read 0xFFFD. Setting the
// PC takes no time.
pc = readmem(0xFFFC) | (readmem(0xFFFD) << 8);
cycles+=2;
// And now we're going to go fetch and operate on the first instruction.
}
void Cpu::brk()
{
pc++;
pushS16(pc);
pushS8(flags | F_B); // FIXME: does this have the missing status bit set?
// FIXME: is setting the BRK bit a 65C02-specific thing? I think it is
FLAG(F_D, 0); // 65c02...
FLAG(F_I, 1);
pc = readmem(0xFFFE) | (uint16_t)(readmem(0xFFFF) << 8);
cycles += 2;
}
void Cpu::irq()
{
// If interrupts are disabled, then do nothing
if (flags & F_I)
return;
pushS16(pc);
flags &= ~F_B; // clear BRK flag
pushS8(flags);
flags |= F_I; // set interrupt flag
pc = readmem(0xFFFE) | (readmem(0xFFFF) << 8);
cycles += 2;
}
uint8_t Cpu::Run(uint8_t numSteps)
{
uint8_t runtime = 0;
while (runtime < numSteps) {
runtime += step();
}
return runtime;
}
uint8_t Cpu::step()
{
uint8_t m = readmem(pc++);
optype_t opcode = opcodes[m];
if (opcode.op == O_ILLEGAL || opcode.mode == A_ILLEGAL) {
m = 0xEA; // substitute O_NOP...
#ifdef VERBOSE_CPU_ERRORS
fprintf(stderr, "** Illegal opcode $%.2X at address $%.4x\n",
m,
pc-1);
#endif
}
// Look at the addressing mode to determine the parameter
uint16_t param = 0;
switch (opcode.mode) {
case A_ILLEGAL:
default:
// This should never happen; we're substituting NOP.
// treat these as IMPLIED
break;
case A_IMP:
// implied: nothing to do. These have a parameter that refers to a
// specific register or particular action to a register
break;
case A_IMM:
// immediate: the next byte at PC
param = pc++;
break;
case A_ABS:
// absolute: the address referred to in the next 2 bytes at PC
param = readmem(pc) | (readmem(pc+1) << 8);
pc += 2;
break;
case A_ABX:
// absolute indexed, based on X
param = (readmem(pc) | (readmem(pc+1) << 8)) + x;
pc += 2;
break;
case A_REL:
// relative
param = (int8_t)readmem(pc++);
param += pc; // do this in 2 steps b/c readmem(pc++) modifies PC
break;
case A_ABI:
// absolute indirect
{
uint16_t addr = readmem(pc) | (readmem(pc+1) << 8);
pc += 2;
param = readmem(addr) | (readmem(addr+1) << 8);
}
break;
case A_ZEX:
// zero-page, indexed by X -- i.e. "ORA $44,X"
param = (readmem(pc++) + x) & 0xFF;
break;
case A_ZER:
// zero-page
param = readmem(pc++);
break;
case A_ZEY:
// zero-page, indexed by Y
param = (readmem(pc++) + y) & 0xFF;
break;
case A_ABY:
// absolute indexed, based on Y
param = (readmem(pc) | (readmem(pc+1) << 8)) + y;
pc += 2;
break;
case A_INY:
// indirect indexed Y - refers to zero-page memory by one byte
{
uint8_t zpL = mmu->read(pc++);
uint8_t zpH = zpL+1;
param = ( mmu->read(zpL) | (mmu->read(zpH) << 8) ) + y;
}
break;
case A_INX:
{
uint8_t zpL = mmu->read(pc++) + x;
uint8_t zpH = zpL+1;
param = ( mmu->read(zpL) | (mmu->read(zpH) << 8) );
}
break;
}
// initialize a counter for the number of cycles this run
// (many opcodes have variable length)
uint8_t cyclesThisStep = opcode.cycles;
// Then look at the opcode type to perform the operations necessary
switch (opcode.op) {
case O_ILLEGAL:
default:
// This should never happen; we're trapping O_ILLEGAL above and substituting O_NOP.
break;
case O_CLD:
FLAG(F_D, 0);
break;
case O_LDX:
x = readmem(param);
SETNZX;
break;
case O_TXS:
sp = x;
break;
case O_LDA:
a = readmem(param);
SETNZA;
break;
case O_STA:
writemem(param, a);
break;
case O_JSR:
pushS16(pc-1);
pc = param;
break;
case O_RTS:
pc = popS16()+1;
break;
case O_PHA:
pushS8(a);
break;
case O_INX:
x++;
SETNZX;
break;
case O_BNE:
if (!(flags & F_Z)) {
pc = param;
cycles++;
}
break;
case O_BVS:
if (flags & F_V) {
pc = param;
cycles++;
}
break;
case O_BRK:
brk();
break;
case O_PHP:
pushS8(flags | F_B);
break;
case O_DEY:
y--;
SETNZY;
break;
case O_CMP:
{
uint16_t tmp = a - readmem(param);
FLAG(F_C, tmp < 0x100);
FLAG(F_Z, !(tmp & 0xFF));
FLAG(F_N, tmp & 0x80);
}
break;
case O_BEQ:
if (flags & F_Z) {
pc = param;
cycles++;
}
break;
case O_TXA:
a = x;
SETNZA;
break;
case O_TYA:
a = y;
SETNZA;
break;
case O_ASL_ACC:
FLAG(F_C, a & 0x80);
a <<= 1;
SETNZA;
break;
case O_ORA:
a |= readmem(param);
SETNZA;
break;
case O_JMP:
pc = param;
break;
case O_DEX:
x--;
SETNZX;
break;
case O_LDY:
y = readmem(param);
SETNZY;
break;
case O_NOP:
break;
case O_TAX:
x = a;
SETNZA;
break;
case O_BPL:
if (!(flags & F_N)) {
pc = param;
cycles++;
}
break;
case O_CLC:
FLAG(F_C, 0);
break;
case O_EOR:
a ^= readmem(param);
SETNZA;
break;
case O_CPY:
{
uint16_t tmp = y - readmem(param);
FLAG(F_C, tmp < 0x100);
FLAG(F_Z, !(tmp & 0xFF));
FLAG(F_N, tmp & 0x80);
}
break;
case O_TSX:
x = sp;
SETNZX;
break;
case O_LSR_ACC:
FLAG(F_C, a & 0x01);
a >>= 1;
SETNZA;
break;
case O_BCC:
if (!(flags & F_C)) {
pc = param;
cycles++;
}
break;
case O_PLA:
a = popS8();
SETNZA;
break;
case O_AND:
a &= readmem(param);
SETNZA;
break;
case O_CPX:
{
uint16_t tmp = x - readmem(param);
FLAG(F_C, tmp < 0x100);
FLAG(F_Z, !(tmp & 0xFF));
FLAG(F_N, tmp & 0x80);
}
break;
case O_BCS:
if (flags & F_C) {
pc = param;
cycles++;
}
break;
case O_BMI:
if (flags & F_N) {
pc = param;
cycles++;
}
break;
case O_TAY:
y = a;
SETNZY;
break;
case O_PLP:
flags = popS8();
FLAG(F_UNK, 1); // ??
break;
case O_BVC:
if (!(flags & F_V)) {
pc = param;
cycles++;
}
break;
case O_INY:
y++;
SETNZY;
break;
case O_STX:
writemem(param, x);
break;
case O_RTI:
flags = popS8();
pc = popS16();
break;
case O_SEC:
FLAG(F_C, 1);
break;
case O_CLI:
FLAG(F_I, 0);
break;
case O_SEI:
FLAG(F_I, 1);
break;
case O_SED:
FLAG(F_D, 1);
break;
case O_CLV:
FLAG(F_V, 0);
break;
case O_STY:
writemem(param, y);
break;
case O_BIT:
{
uint8_t m = readmem(param);
uint8_t v = a & m;
FLAG(F_N, (v & 0x80) | (m & 0x80));
FLAG(F_Z, v == 0);
FLAG(F_V, m & 0x40);
// status = (status & 0x3F) | (uint8_t)(m & 0xC0);
}
break;
case O_ROL_ACC:
{
uint8_t v = a << 1;
if (flags & F_C)
v |= 0x01;
FLAG(F_C, a & 0x80);
a = v;
SETNZA;
}
break;
case O_ROR_ACC:
{
uint8_t v = a >> 1;
if (flags & F_C)
v |= 0x80;
FLAG(F_C, a & 0x01);
a = v;
SETNZA;
}
break;
case O_ASL:
{
uint8_t v = readmem(param);
FLAG(F_C, v & 0x80);
v <<= 1;
FLAG(F_N, v & 0x80);
FLAG(F_Z, v == 0);
writemem(param, v);
}
break;
case O_LSR:
{
uint8_t v = readmem(param);
FLAG(F_C, v & 0x01);
v >>= 1;
FLAG(F_N, 0);
FLAG(F_Z, v == 0);
writemem(param, v);
}
break;
case O_ROL:
{
uint8_t m = readmem(param);
uint8_t v = m << 1;
if (flags & F_C)
v |= 0x01;
FLAG(F_C, m & 0x80);
FLAG(F_N, v & 0x80);
FLAG(F_Z, v == 0);
writemem(param, v);
}
break;
case O_ROR:
{
uint8_t m = readmem(param);
uint8_t v = m >> 1;
if (flags & F_C)
v |= 0x80;
FLAG(F_C, m & 0x01);
FLAG(F_N, v & 0x80);
FLAG(F_Z, v == 0);
writemem(param, v);
}
break;
case O_INC:
{
uint8_t v = mmu->read(param) + 1;
FLAG(F_N, v & 0x80);
FLAG(F_Z, v == 0);
writemem(param, v);
}
break;
case O_DEC:
{
uint8_t v = mmu->read(param) - 1;
FLAG(F_N, v & 0x80);
FLAG(F_Z, v == 0);
writemem(param, v);
}
break;
case O_DCP:
// not a real opcode; one of the 65c02 side-effect "illegal" opcodes
{
uint8_t v = mmu->read(param) - 1;
FLAG(F_N, v & 0x80);
FLAG(F_Z, v == 0);
writemem(param, v);
uint16_t tmp = a - v;
FLAG(F_C, tmp < 0x100);
FLAG(F_Z, !(tmp & 0xFF));
FLAG(F_N, tmp & 0x80);
}
break;
case O_SBC:
{
uint8_t memTemp = readmem(param) ^ 0xFF;
int16_t c;
uint8_t v;
if (flags & F_D) {
cycles++;
c = (a & 0x0F) + (memTemp & 0x0F) + (flags & F_C);
if (c < 0x10)
c = (c - 0x06) & 0x0f;
c += (a & 0xf0) + (memTemp & 0xf0);
v = (c >> 1) ^ c;
if (c < 0x100)
c = (c + 0xa0) & 0xff;
} else {
c = a + memTemp + (flags & F_C);
v = (c ^ a) & 0x80;
}
if (((a ^ memTemp) & 0x80) != 0) {
v = 0;
}
FLAG(F_C, c > 0xFF);
FLAG(F_V, v);
a = c & 0xFF;
SETNZA;
}
break;
case O_ADC:
{
uint8_t memTemp = readmem(param);
int16_t c;
uint8_t v;
if (flags & F_D) {
cycles++;
c = (a & 0x0F) + (memTemp & 0x0F) + (flags & F_C);
if (c > 0x09)
c = (c - 0x0a) | 0x10;
c += (a & 0xf0) + (memTemp & 0xf0);
v = (c >> 1) ^ c;
if (c > 0x99)
c += 0x60;
} else {
c = a + memTemp + (flags & F_C);
v = (c ^ a) & 0x80;
}
if (((a ^ memTemp) & 0x80) != 0) {
v = 0;
}
FLAG(F_C, c > 0xFF);
FLAG(F_V, v);
a = c & 0xFF;
SETNZA;
}
break;
case O_PHX:
pushS8(x);
break;
case O_PHY:
pushS8(y);
break;
case O_PLY:
y = popS8();
SETNZY;
break;
case O_PLX:
x = popS8();
SETNZX;
break;
case O_BRA:
pc = param;
break;
// ***
}
// And finally update our executed cycle count with the runtime
cycles += cyclesThisStep;
return cyclesThisStep;
}
uint8_t Cpu::X()
{
return x;
}
uint8_t Cpu::Y()
{
return y;
}
uint8_t Cpu::A()
{
return a;
}
uint16_t Cpu::PC()
{
return pc;
}
uint8_t Cpu::SP()
{
return sp;
}
uint8_t Cpu::P()
{
return flags;
}
void Cpu::pushS8(uint8_t b)
{
writemem(0x100 + sp, b);
sp--; // may underflow (does this at startup)
}
void Cpu::pushS16(uint16_t w)
{
pushS8((w >> 8) & 0xFF);
pushS8(w & 0xFF);
}
uint8_t Cpu::popS8()
{
sp++; // may overflow
return readmem(0x100 + sp);
}
uint16_t Cpu::popS16()
{
uint8_t lsb = popS8();
uint8_t msb = popS8();
return (msb << 8) | lsb;
}
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