diff options
Diffstat (limited to 'src')
| -rw-r--r-- | src/mos6502.rs | 285 |
1 files changed, 181 insertions, 104 deletions
diff --git a/src/mos6502.rs b/src/mos6502.rs index 2ebd37f..d60b042 100644 --- a/src/mos6502.rs +++ b/src/mos6502.rs @@ -42,6 +42,44 @@ macro_rules! make_addrtable { ];); } +const INST_LENGTH: [u8; 0x100] = [ + 0, 2, 0, 0, 0, 2, 2, 0, 0, 2, 1, 0, 0, 3, 3, 0, + 2, 2, 0, 0, 0, 2, 2, 0, 0, 3, 0, 0, 0, 3, 3, 0, + 3, 2, 0, 0, 2, 2, 2, 0, 0, 2, 1, 0, 3, 3, 3, 0, + 2, 2, 0, 0, 0, 2, 2, 0, 0, 3, 0, 0, 0, 3, 3, 0, + 0, 2, 0, 0, 0, 2, 2, 0, 0, 2, 1, 0, 3, 3, 3, 0, + 2, 2, 0, 0, 0, 2, 2, 0, 0, 3, 0, 0, 0, 3, 3, 0, + 0, 2, 0, 0, 0, 2, 2, 0, 0, 2, 1, 0, 3, 3, 3, 0, + 2, 2, 0, 0, 0, 2, 2, 0, 0, 3, 0, 0, 0, 3, 3, 0, + 0, 2, 0, 0, 2, 2, 2, 0, 0, 0, 0, 0, 3, 3, 3, 0, + 2, 2, 0, 0, 2, 2, 2, 0, 0, 3, 0, 0, 0, 3, 0, 0, + 2, 2, 2, 0, 2, 2, 2, 0, 0, 2, 0, 0, 3, 3, 3, 0, + 2, 2, 0, 0, 2, 2, 2, 0, 0, 3, 0, 0, 3, 3, 3, 0, + 2, 2, 0, 0, 2, 2, 2, 0, 0, 2, 0, 0, 3, 3, 3, 0, + 2, 2, 0, 0, 0, 2, 2, 0, 0, 3, 0, 0, 0, 3, 3, 0, + 2, 2, 0, 0, 2, 2, 2, 0, 0, 2, 0, 0, 3, 3, 3, 0, + 2, 2, 0, 0, 0, 2, 2, 0, 0, 3, 0, 0, 0, 3, 3, 0, +]; + +const INST_CYCLE: [u8; 0x100] = [ + 0, 6, 0, 0, 0, 3, 5, 0, 0, 2, 2, 0, 0, 4, 6, 0, + 2, 5, 0, 0, 0, 4, 6, 0, 0, 4, 0, 0, 0, 4, 7, 0, + 6, 6, 0, 0, 3, 3, 5, 0, 0, 2, 2, 0, 4, 4, 6, 0, + 2, 5, 0, 0, 0, 4, 6, 0, 0, 4, 0, 0, 0, 4, 7, 0, + 0, 6, 0, 0, 0, 3, 5, 0, 0, 2, 2, 0, 3, 4, 6, 0, + 2, 5, 0, 0, 0, 4, 6, 0, 0, 4, 0, 0, 0, 4, 7, 0, + 0, 6, 0, 0, 0, 3, 5, 0, 0, 2, 2, 0, 5, 4, 6, 0, + 2, 5, 0, 0, 0, 4, 6, 0, 0, 4, 0, 0, 0, 4, 7, 0, + 0, 6, 0, 0, 3, 3, 3, 0, 0, 0, 0, 0, 4, 4, 4, 0, + 2, 6, 0, 0, 4, 4, 4, 0, 0, 5, 0, 0, 0, 5, 0, 0, + 2, 6, 2, 0, 3, 3, 3, 0, 0, 2, 0, 0, 4, 4, 4, 0, + 2, 5, 0, 0, 4, 4, 4, 0, 0, 4, 0, 0, 4, 4, 4, 0, + 2, 6, 0, 0, 3, 3, 5, 0, 0, 2, 0, 0, 4, 4, 6, 0, + 2, 5, 0, 0, 0, 4, 6, 0, 0, 4, 0, 0, 0, 4, 7, 0, + 2, 6, 0, 0, 3, 3, 5, 0, 0, 2, 0, 0, 4, 4, 6, 0, + 2, 5, 0, 0, 0, 4, 6, 0, 0, 4, 0, 0, 0, 4, 7, 0, +]; + macro_rules! ids2strs { ($($x:ident), *) => { $(#[allow(non_upper_case_globals)] @@ -175,6 +213,8 @@ mod ops { ($st: ident, $r: expr) => ($st |= ($r as u8 & NEG_FLAG) as u8); } + /* arithmetic */ + fn adc(cpu: &mut CPU) { let opr1 = cpu.a as u16; let opr2 = match cpu.addr_mode { @@ -212,6 +252,57 @@ mod ops { cpu.status = status; } + macro_rules! make_cmp { + ($f: ident, $r: ident) => (fn $f(cpu: &mut CPU) { + let opr1 = cpu.$r as u16; + let opr2 = match cpu.addr_mode { + AddrMode::Immediate => cpu.imm_val, + _ => cpu.mem.read(cpu.ea) + } as u16; + let res = opr1 - opr2; + let mut status = cpu.status & !(CARRY_FLAG | ZERO_FLAG | NEG_FLAG); + status |= (res < 0x100) as u8; /* carry flag */ + check_zero!(status, res); + check_neg!(status, res); + cpu.status = status; + }); + } + + make_cmp!(cmp, a); + make_cmp!(cpx, x); + make_cmp!(cpy, y); + + /* increments & decrements */ + macro_rules! make_delta { + ($f: ident, $d: expr) => ( + fn $f(cpu: &mut CPU) { + let res = cpu.mem.read(cpu.ea) as u16 + $d; + let mut status = cpu.status & !(ZERO_FLAG | NEG_FLAG); + cpu.mem.write(cpu.ea, res as u8); + check_zero!(status, res); + check_neg!(status, res); + cpu.status = status; + }); + ($f: ident, $d: expr, $r: ident) => ( + fn $f(cpu: &mut CPU) { + let res = cpu.$r as u16 + $d; + let mut status = cpu.status & !(ZERO_FLAG | NEG_FLAG); + cpu.$r = res as u8; + check_zero!(status, res); + check_neg!(status, res); + cpu.status = status; + }); + + } + + make_delta!(dec, 0xff); + make_delta!(dex, 0xff, x); + make_delta!(dey, 0xff, y); + make_delta!(inc, 0x01); + make_delta!(inx, 0x01, x); + make_delta!(iny, 0x01, y); + + /* logical */ macro_rules! make_logic { ($f: ident, $op: tt) => ( fn $f(cpu: &mut CPU) { @@ -231,6 +322,15 @@ mod ops { make_logic!(eor, ^); make_logic!(ora, |); + fn bit(cpu: &mut CPU) { + let m = cpu.mem.read(cpu.ea); + let mut status = cpu.status & !(ZERO_FLAG | OVER_FLAG | NEG_FLAG); + check_zero!(status, (m & cpu.a)); + status |= ((m >> 6) & 0x3) << 6; /* copy bit 6 & 7 */ + cpu.status = status; + } + + /* shifts */ fn asl(cpu: &mut CPU) { let res = match cpu.addr_mode { AddrMode::Accumulator => { @@ -244,7 +344,7 @@ mod ops { t }}; let mut status = cpu.status & !(CARRY_FLAG | ZERO_FLAG | NEG_FLAG); - status |= (res > 0xff) as u8; /* carry flag */ + status |= (res >> 8) as u8; /* carry flag */ check_zero!(status, res); check_neg!(status, res); cpu.status = status; @@ -316,20 +416,13 @@ mod ops { cpu.status = status; } - fn bit(cpu: &mut CPU) { - let m = cpu.mem.read(cpu.ea); - let mut status = cpu.status & !(ZERO_FLAG | OVER_FLAG | NEG_FLAG); - check_zero!(status, (m & cpu.a)); - status |= ((m >> 6) & 0x3) << 6; /* copy bit 6 & 7 */ - cpu.status = status; - } - + /* branches */ macro_rules! make_branch_clear { ($f: ident, $e: ident) => (fn $f(cpu: &mut CPU) { match cpu.$e() { 0 => { - cpu.pc = (cpu.pc as i32 + cpu.ea as i32) as u16; - cpu.cycle.wrapping_add(1); + cpu.pc = cpu.ea; + cpu.cycle += 1; }, _ => () }}); @@ -340,8 +433,8 @@ mod ops { match cpu.$e() { 0 => (), _ => { - cpu.pc = (cpu.pc as i32 + cpu.ea as i32) as u16; - cpu.cycle.wrapping_add(1); + cpu.pc = cpu.ea; + cpu.cycle += 1; } }}); } @@ -360,16 +453,17 @@ mod ops { } fn brk(cpu: &mut CPU) { - let npc = cpu.pc.wrapping_add(2); + let pc = cpu.pc; let sp = cpu.sp; - cpu.mem.write(stack_addr!(sp, 0), (npc >> 8) as u8); /* push high pc */ - cpu.mem.write(stack_addr!(sp, 1), npc as u8); /* push low pc */ + cpu.mem.write(stack_addr!(sp, 0), (pc >> 8) as u8); /* push high pc */ + cpu.mem.write(stack_addr!(sp, 1), pc as u8); /* push low pc */ cpu.status |= BRK_FLAG; cpu.mem.write(stack_addr!(sp, 2), cpu.status); /* push status */ cpu.sp = sp.wrapping_sub(3); cpu.pc = read16!(cpu.mem, 0xfffe as u16); /* load the interrupt vector */ } + /* status flag changes */ fn clc(cpu: &mut CPU) { cpu.status &= !CARRY_FLAG; } fn cld(cpu: &mut CPU) { cpu.status &= !DEC_FLAG; } fn cli(cpu: &mut CPU) { cpu.status &= !INT_FLAG; } @@ -379,56 +473,7 @@ mod ops { fn sed(cpu: &mut CPU) { cpu.status |= DEC_FLAG; } fn sei(cpu: &mut CPU) { cpu.status |= INT_FLAG; } - - macro_rules! make_cmp { - ($f: ident, $r: ident) => (fn $f(cpu: &mut CPU) { - let opr1 = cpu.$r as u16; - let opr2 = match cpu.addr_mode { - AddrMode::Immediate => cpu.imm_val, - _ => cpu.mem.read(cpu.ea) - } as u16; - let res = opr1 - opr2; - let mut status = cpu.status & !(CARRY_FLAG | ZERO_FLAG | NEG_FLAG); - status |= (res < 0x100) as u8; /* carry flag */ - check_zero!(status, res); - check_neg!(status, res); - cpu.status = status; - }); - } - - make_cmp!(cmp, a); - make_cmp!(cpx, x); - make_cmp!(cpy, y); - - macro_rules! make_delta { - ($f: ident, $d: expr) => ( - fn $f(cpu: &mut CPU) { - let res = cpu.mem.read(cpu.ea) as u16 + $d; - let mut status = cpu.status & !(ZERO_FLAG | NEG_FLAG); - cpu.mem.write(cpu.ea, res as u8); - check_zero!(status, res); - check_neg!(status, res); - cpu.status = status; - }); - ($f: ident, $d: expr, $r: ident) => ( - fn $f(cpu: &mut CPU) { - let res = cpu.$r as u16 + $d; - let mut status = cpu.status & !(ZERO_FLAG | NEG_FLAG); - cpu.$r = res as u8; - check_zero!(status, res); - check_neg!(status, res); - cpu.status = status; - }); - - } - - make_delta!(dec, 0xff); - make_delta!(dex, 0xff, x); - make_delta!(dey, 0xff, y); - make_delta!(inc, 0x01); - make_delta!(inx, 0x01, x); - make_delta!(iny, 0x01, y); - + /* jumps & calls */ fn jmp(cpu: &mut CPU) { cpu.pc = cpu.ea; } fn jsr(cpu: &mut CPU) { @@ -440,6 +485,25 @@ mod ops { cpu.pc = cpu.ea; } + fn rts(cpu: &mut CPU) { + let sp = cpu.sp.wrapping_add(2); + cpu.pc = make16!(cpu.mem.read(stack_addr!(sp, 0)), + cpu.mem.read(stack_addr!(sp, 1))).wrapping_add(1); + cpu.sp = sp; + } + + /* system functions */ + fn rti(cpu: &mut CPU) { + let sp = cpu.sp.wrapping_add(3); + cpu.status = cpu.mem.read(stack_addr!(sp, 2)); + cpu.pc = make16!(cpu.mem.read(stack_addr!(sp, 0)), + cpu.mem.read(stack_addr!(sp, 1))); + cpu.sp = sp; + } + + fn nop(_cpu: &mut CPU) {} + + /* load/store operations */ macro_rules! make_ld { ($f: ident, $r: ident) => (fn $f(cpu: &mut CPU) { let mut status = cpu.status & !(ZERO_FLAG | NEG_FLAG); @@ -465,6 +529,7 @@ mod ops { make_st!(stx, x); make_st!(sty, y); + /* register transfers */ macro_rules! make_trans { ($f: ident, $from: ident, $to: ident) => (fn $f(cpu: &mut CPU) { let mut status = cpu.status & !(ZERO_FLAG | NEG_FLAG); @@ -478,11 +543,13 @@ mod ops { make_trans!(tax, a, x); make_trans!(tay, a, y); - make_trans!(tsx, sp, x); make_trans!(txa, x, a); - make_trans!(txs, x, sp); make_trans!(tya, y, a); + /* stack operations */ + make_trans!(tsx, sp, x); + fn txs(cpu: &mut CPU) { cpu.sp = cpu.x; } + fn pha(cpu: &mut CPU) { let sp = cpu.sp; cpu.mem.write(stack_addr!(sp, 0), cpu.a); @@ -512,22 +579,6 @@ mod ops { cpu.sp = sp; } - fn rti(cpu: &mut CPU) { - let sp = cpu.sp.wrapping_add(3); - cpu.status = cpu.mem.read(stack_addr!(sp, 2)); - cpu.pc = make16!(cpu.mem.read(stack_addr!(sp, 0)), - cpu.mem.read(stack_addr!(sp, 1))); - cpu.sp = sp; - } - - fn rts(cpu: &mut CPU) { - let sp = cpu.sp.wrapping_add(2); - cpu.pc = make16!(cpu.mem.read(stack_addr!(sp, 0)), - cpu.mem.read(stack_addr!(sp, 1))).wrapping_add(1); - cpu.sp = sp; - } - - fn nop(_cpu: &mut CPU) {} fn nil(cpu: &mut CPU) { panic!("invalid instruction: 0x{:02x}", cpu.mem.read(cpu.pc)); } @@ -543,65 +594,77 @@ mod addr { fn imm(cpu: &mut CPU) { cpu.addr_mode = AddrMode::Immediate; - cpu.imm_val = cpu.mem.read(cpu.pc.wrapping_add(1)); + cpu.imm_val = cpu.mem.read(cpu.opr); } fn zpg(cpu: &mut CPU) { cpu.addr_mode = AddrMode::EffAddr; - cpu.ea = cpu.mem.read(cpu.pc.wrapping_add(1)) as u16; + cpu.ea = cpu.mem.read(cpu.opr) as u16; } fn zpx(cpu: &mut CPU) { cpu.addr_mode = AddrMode::EffAddr; - cpu.ea = (cpu.mem.read(cpu.pc.wrapping_add(1)) + cpu.ea = (cpu.mem.read(cpu.opr) .wrapping_add(cpu.x)) as u16; } fn zpy(cpu: &mut CPU) { cpu.addr_mode = AddrMode::EffAddr; - cpu.ea = (cpu.mem.read(cpu.pc.wrapping_add(1)) + cpu.ea = (cpu.mem.read(cpu.opr) .wrapping_add(cpu.y)) as u16; } fn rel(cpu: &mut CPU) { cpu.addr_mode = AddrMode::EffAddr; - cpu.ea = cpu.mem.read(cpu.pc.wrapping_add(1)) as u16; + let base = cpu.pc; + let offset = cpu.mem.read(cpu.opr) as i8 as i16; + let sum = (base & 0xff) + offset as u16; + cpu.ea = (base & 0xff00).wrapping_add(sum); + cpu.cycle += (sum >> 8) as u32; } fn abs(cpu: &mut CPU) { cpu.addr_mode = AddrMode::EffAddr; - cpu.ea = read16!(cpu.mem, cpu.pc.wrapping_add(1)); + cpu.ea = read16!(cpu.mem, cpu.opr); } fn abx(cpu: &mut CPU) { cpu.addr_mode = AddrMode::EffAddr; - cpu.ea = read16!(cpu.mem, cpu.pc.wrapping_add(1)) - .wrapping_add(cpu.x as u16); + let base = read16!(cpu.mem, cpu.opr); + let sum = (base & 0xff) + cpu.x as u16; + cpu.ea = (base & 0xff00).wrapping_add(sum); + cpu.cycle += (sum >> 8) as u32; /* boundary cross if carry */ } fn aby(cpu: &mut CPU) { cpu.addr_mode = AddrMode::EffAddr; - cpu.ea = read16!(cpu.mem, cpu.pc.wrapping_add(1)) - .wrapping_add(cpu.y as u16); + let base = read16!(cpu.mem, cpu.opr); + let sum = (base & 0xff) + cpu.y as u16; + cpu.ea = (base & 0xff00).wrapping_add(sum); + cpu.cycle += (sum >> 8) as u32; /* boundary cross if carry */ } fn ind(cpu: &mut CPU) { cpu.addr_mode = AddrMode::EffAddr; - let addr = read16!(cpu.mem, cpu.pc.wrapping_add(1)); + let addr = read16!(cpu.mem, cpu.opr); cpu.ea = read16!(cpu.mem, addr); } fn xin(cpu: &mut CPU) { cpu.addr_mode = AddrMode::EffAddr; - let addr = cpu.mem.read(cpu.mem.read(cpu.pc.wrapping_add(1)) - .wrapping_add(cpu.x) as u16) as u16; + let addr = cpu.mem.read( + cpu.mem.read(cpu.opr) + .wrapping_add(cpu.x) as u16) as u16; cpu.ea = read16!(cpu.mem, addr); } fn iny(cpu: &mut CPU) { cpu.addr_mode = AddrMode::EffAddr; - let addr = cpu.mem.read(cpu.mem.read(cpu.pc.wrapping_add(1)) as u16) as u16; - cpu.ea = read16!(cpu.mem, addr).wrapping_add(cpu.y as u16); + let addr = cpu.mem.read(cpu.mem.read(cpu.opr) as u16) as u16; + let base = read16!(cpu.mem, addr); + let sum = (base & 0xff) + cpu.y as u16; + cpu.ea = (base & 0xff00).wrapping_add(sum); + cpu.cycle += (sum >> 8) as u32; /* boundary cross if carry */ } fn nil(_cpu: &mut CPU) {} @@ -663,6 +726,7 @@ pub struct CPU<'a> { sp: u8, /* internal state */ addr_mode: AddrMode, + opr: u16, ea: u16, /* effective address */ imm_val: u8, cycle: u32, @@ -670,18 +734,31 @@ pub struct CPU<'a> { } impl<'a> CPU<'a> { - fn step(&mut self, opcode: u8) { - ops::OPS[opcode as usize](self); - addr::ADDR_MODES[opcode as usize](self); - } #[inline(always)] pub fn get_carry(&self) -> u8 { (self.status >> 0) & 1 } #[inline(always)] pub fn get_zero(&self) -> u8 { (self.status >> 1) & 1 } #[inline(always)] pub fn get_over(&self) -> u8 { (self.status >> 6) & 1 } #[inline(always)] pub fn get_neg(&self) -> u8 { (self.status >> 7) & 1 } + pub fn new(mem: &'a mut VMem) -> Self { - CPU{a: 0, x: 0, y: 0, status: 0, pc: 0, sp: 0, ea: 0, cycle: 0, + CPU{a: 0, x: 0, y: 0, + pc: 0, sp: 0, status: 0, + opr: 0, ea: 0, cycle: 0, addr_mode: AddrMode::EffAddr, imm_val: 0, mem} } + + pub fn step(&mut self) { + let pc = self.pc; + let opcode = self.mem.read(pc) as usize; + /* update opr pointing to operands of current inst */ + self.opr = pc.wrapping_add(1); + /* update program counter pointing to next inst */ + self.pc = pc.wrapping_add(INST_LENGTH[opcode] as u16); + /* get effective address based on addressing mode */ + addr::ADDR_MODES[opcode](self); + /* execute the inst */ + ops::OPS[opcode](self); + self.cycle += INST_CYCLE[opcode] as u32; + } } |