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SmartStack improvements. Can now detect the rti shim for restoring ba…
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…nks when leaving interrupt logic.
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@indigodarkwolf
indigodarkwolf committed Dec 5, 2023
1 parent 4d195ab commit bb03daa
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Showing 8 changed files with 201 additions and 46 deletions.
31 changes: 19 additions & 12 deletions src/cpu/fake6502.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -94,7 +94,8 @@ uint8_t debug6502 = 0;
uint8_t penaltyop, penaltyaddr;
uint8_t waiting = 0;

_smart_stack stack6502[256];
_smart_stack stack6502[256];
uint8_t stack6502_underflow = 0;

// externally supplied functions
extern uint8_t read6502(uint16_t address);
Expand Down Expand Up @@ -128,9 +129,11 @@ static void putvalue(uint16_t saveval)

void nmi6502()
{
auto &ss = stack6502[state6502.sp_depth++];
ss.source_pc = state6502.pc;
auto &ss = stack6502[state6502.sp_depth++];
ss.source_pc = state6502.pc;
ss.source_bank = bank6502(state6502.pc);
ss.push_depth = 0;
state6502.sp_unwind_depth = state6502.sp_depth;

push16(state6502.pc);
push8(state6502.status & ~FLAG_BREAK);
Expand All @@ -140,18 +143,21 @@ void nmi6502()
state6502.pc = (uint16_t)read6502(0xFFFA) | ((uint16_t)read6502(0xFFFB) << 8);
waiting = 0;

ss.dest_pc = state6502.pc;
ss.dest_pc = state6502.pc;
ss.dest_bank = bank6502(state6502.pc);
ss.op_type = _stack_op_type::nmi;
ss.opcode = 0;
ss.op_type = _stack_op_type::nmi;
ss.pop_type = _stack_pop_type::unknown;
ss.opcode = 0;
}

void irq6502()
{
if (!(state6502.status & FLAG_INTERRUPT)) {
auto &ss = stack6502[state6502.sp_depth++];
ss.source_pc = state6502.pc;
auto &ss = stack6502[state6502.sp_depth++];
ss.source_pc = state6502.pc;
ss.source_bank = bank6502(state6502.pc);
ss.push_depth = 0;
state6502.sp_unwind_depth = state6502.sp_depth;

push16(state6502.pc);
push8(state6502.status & ~FLAG_BREAK);
Expand All @@ -160,10 +166,11 @@ void irq6502()
vp6502();
state6502.pc = (uint16_t)read6502(0xFFFE) | ((uint16_t)read6502(0xFFFF) << 8);

ss.dest_pc = state6502.pc;
ss.dest_pc = state6502.pc;
ss.dest_bank = bank6502(state6502.pc);
ss.op_type = _stack_op_type::irq;
ss.opcode = 0;
ss.pop_type = _stack_pop_type::unknown;
ss.opcode = 0;
}
waiting = 0;
}
Expand Down Expand Up @@ -198,7 +205,7 @@ void exec6502(uint32_t tickcount)
(*addrtable[opcode])();
(*optable[opcode])();

if (debug6502 & (DEBUG6502_READ | DEBUG6502_WRITE)) {
if ((debug6502 & (DEBUG6502_READ | DEBUG6502_WRITE)) || stack6502_underflow) {
state6502 = debug_state6502;
clockticks6502 = debug_clockticks6502;
return;
Expand Down Expand Up @@ -240,7 +247,7 @@ void step6502()
(*addrtable[opcode])();
(*optable[opcode])();

if (debug6502 & (DEBUG6502_READ | DEBUG6502_WRITE)) {
if ((debug6502 & (DEBUG6502_READ | DEBUG6502_WRITE)) || stack6502_underflow) {
state6502 = debug_state6502;
clockticks6502 = debug_clockticks6502;
return;
Expand Down
43 changes: 35 additions & 8 deletions src/cpu/fake6502.h
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Original file line number Diff line number Diff line change
Expand Up @@ -13,23 +13,50 @@

struct _state6502 {
uint16_t pc;
uint8_t sp_depth;
uint8_t sp_depth;
uint8_t sp_unwind_depth;
uint8_t sp, a, x, y, status;
};

enum class _stack_op_type : uint8_t {
op,
nmi,
irq,
jsr,
smart,
};

enum class _stack_pop_type : uint8_t {
unknown,
rts,
rti
};

enum class _push_op_type : uint8_t {
unknown,
a,
x,
y,
status
};

struct _smart_stack_ex {
_push_op_type push_type;
_push_op_type pull_type;
uint8_t value;
};

struct _smart_stack {
uint16_t source_pc;
uint16_t dest_pc;
uint8_t source_bank;
uint8_t dest_bank;
_stack_op_type op_type;
uint8_t opcode;
uint16_t source_pc;
uint16_t dest_pc;
uint8_t source_bank;
uint8_t dest_bank;
_stack_op_type op_type;
_stack_pop_type pop_type;
uint16_t pop_pc;
uint8_t pop_bank;
uint8_t opcode;
uint8_t push_depth;
_smart_stack_ex pushed_bytes[256];
};

extern void init6502();
Expand Down
58 changes: 56 additions & 2 deletions src/cpu/instructions_6502.h
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Original file line number Diff line number Diff line change
Expand Up @@ -375,13 +375,16 @@ jsr()
auto &ss = stack6502[state6502.sp_depth++];
ss.source_pc = state6502.pc;
ss.source_bank = bank6502(state6502.pc);
ss.push_depth = 0;
state6502.sp_unwind_depth = state6502.sp_depth;

push16(state6502.pc - 1);
state6502.pc = ea;

ss.dest_pc = state6502.pc;
ss.dest_bank = bank6502(state6502.pc);
ss.op_type = _stack_op_type::op;
ss.op_type = _stack_op_type::jsr;
ss.pop_type = _stack_pop_type::unknown;
ss.opcode = opcode;
}

Expand Down Expand Up @@ -466,12 +469,38 @@ static void
pha()
{
push8(state6502.a);
auto &ss = stack6502[(state6502.sp_depth + 255) & 0xff];
auto &ssx = ss.pushed_bytes[ss.push_depth++];
ssx.push_type = _push_op_type::a;
ssx.pull_type = _push_op_type::unknown;
ssx.value = state6502.a;
}

static void
php()
{
push8(state6502.status | FLAG_BREAK);
auto &ss = stack6502[(state6502.sp_depth + 255) & 0xff];
auto &ssx = ss.pushed_bytes[ss.push_depth++];
ssx.push_type = _push_op_type::status;
ssx.pull_type = _push_op_type::unknown;
ssx.value = state6502.status | FLAG_BREAK;

if (ss.op_type != _stack_op_type::jsr && ss.push_depth == 5) {
ss.push_depth -= 3;

auto &ss2 = stack6502[state6502.sp_depth++];
ss2.source_pc = (static_cast<uint16_t>(ss.pushed_bytes[ss.push_depth].value) << 8) | static_cast<uint16_t>(ss.pushed_bytes[ss.push_depth+1].value);
ss2.source_bank = bank6502(state6502.pc);
ss2.push_depth = 0;
state6502.sp_unwind_depth = state6502.sp_depth;

ss2.dest_pc = state6502.pc;
ss2.dest_bank = bank6502(state6502.pc);
ss2.op_type = _stack_op_type::smart;
ss2.pop_type = _stack_pop_type::unknown;
ss2.opcode = 0;
}
}

static void
Expand All @@ -481,12 +510,22 @@ pla()

zerocalc(state6502.a);
signcalc(state6502.a);

auto &ss = stack6502[(state6502.sp_depth + 255) & 0xff];
ss.push_depth -= !!ss.push_depth;
auto &ssx = ss.pushed_bytes[ss.push_depth];
ssx.pull_type = _push_op_type::a;
}

static void
plp()
{
state6502.status = pull8() | FLAG_CONSTANT;

auto &ss = stack6502[(state6502.sp_depth + 255) & 0xff];
ss.push_depth -= !!ss.push_depth;
auto &ssx = ss.pushed_bytes[ss.push_depth];
ssx.pull_type = _push_op_type::status;
}

static void
Expand Down Expand Up @@ -521,18 +560,33 @@ ror()
static void
rti()
{
const uint16_t old_pc = state6502.pc;
state6502.status = pull8();
value = pull16();
state6502.pc = value;
stack6502_underflow |= !state6502.sp_depth;
state6502.sp_depth -= !!state6502.sp_depth;

auto &ss = stack6502[state6502.sp_depth];
ss.pop_type = _stack_pop_type::rti;
ss.pop_pc = old_pc - 1;
ss.pop_bank = bank6502(old_pc);
}

static void
rts()
{
value = pull16();
const uint16_t old_pc = state6502.pc;

value = pull16();
state6502.pc = value + 1;
stack6502_underflow |= !state6502.sp_depth;
state6502.sp_depth -= !!state6502.sp_depth;

auto &ss = stack6502[state6502.sp_depth];
ss.pop_type = _stack_pop_type::rts;
ss.pop_pc = old_pc - 1;
ss.pop_bank = bank6502(old_pc);
}

static void
Expand Down
20 changes: 20 additions & 0 deletions src/cpu/instructions_65c02.h
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Original file line number Diff line number Diff line change
Expand Up @@ -84,6 +84,11 @@ static void
phx()
{
push8(state6502.x);
auto &ss = stack6502[(state6502.sp_depth + 255) & 0xff];
auto &ssx = ss.pushed_bytes[ss.push_depth++];
ssx.push_type = _push_op_type::x;
ssx.pull_type = _push_op_type::unknown;
ssx.value = state6502.x;
}

static void
Expand All @@ -93,12 +98,22 @@ plx()

zerocalc(state6502.x);
signcalc(state6502.x);

auto &ss = stack6502[(state6502.sp_depth + 255) & 0xff];
ss.push_depth -= !!ss.push_depth;
auto &ssx = ss.pushed_bytes[ss.push_depth];
ssx.pull_type = _push_op_type::x;
}

static void
phy()
{
push8(state6502.y);
auto &ss = stack6502[(state6502.sp_depth + 255) & 0xff];
auto &ssx = ss.pushed_bytes[ss.push_depth++];
ssx.push_type = _push_op_type::y;
ssx.pull_type = _push_op_type::unknown;
ssx.value = state6502.y;
}

static void
Expand All @@ -108,6 +123,11 @@ ply()

zerocalc(state6502.y);
signcalc(state6502.y);

auto &ss = stack6502[(state6502.sp_depth + 255) & 0xff];
ss.push_depth -= !!ss.push_depth;
auto &ssx = ss.pushed_bytes[ss.push_depth];
ssx.pull_type = _push_op_type::y;
}

// *******************************************************************************************
Expand Down
14 changes: 8 additions & 6 deletions src/cpu/support.h
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Original file line number Diff line number Diff line change
Expand Up @@ -85,13 +85,15 @@ uint8_t pull8()
void reset6502()
{
vp6502();
state6502.pc = (uint16_t)read6502(0xFFFC) | ((uint16_t)read6502(0xFFFD) << 8);
state6502.sp_depth = 0;
state6502.a = 0;
state6502.x = 0;
state6502.y = 0;
state6502.sp = 0xFD;
state6502.pc = (uint16_t)read6502(0xFFFC) | ((uint16_t)read6502(0xFFFD) << 8);
state6502.sp_depth = 0;
state6502.sp_unwind_depth = 0;
state6502.a = 0;
state6502.x = 0;
state6502.y = 0;
state6502.sp = 0xFD;
state6502.status |= FLAG_CONSTANT | FLAG_BREAK;
stack6502_underflow = 0;
setinterrupt();
cleardecimal();
waiting = 0;
Expand Down
1 change: 1 addition & 0 deletions src/glue.h
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Original file line number Diff line number Diff line change
Expand Up @@ -28,6 +28,7 @@
extern _state6502 state6502;
extern uint8_t waiting;
extern _smart_stack stack6502[256];
extern uint8_t stack6502_underflow;

extern uint8_t *RAM;
extern uint8_t ROM[ROM_SIZE];
Expand Down
2 changes: 1 addition & 1 deletion src/main.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -418,7 +418,7 @@ void emulator_loop()

uint64_t old_clockticks6502 = clockticks6502;
step6502();
if (debug6502) {
if (debug6502 || stack6502_underflow) {
debugger_process_cpu();
if (debugger_is_paused()) {
continue;
Expand Down
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