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-rw-r--r--src/mos6502.rs285
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;
+ }
}