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Merge pull request #73 from matheusgomes28/adding-remaining-cmp-opcodes
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Adding support for remaining CMP opcodes:
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@matheusgomes28
matheusgomes28 authored Oct 15, 2024
2 parents 9e809f4 + 37cf4aa commit 3056b08
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16 changes: 8 additions & 8 deletions README.md
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Original file line number Diff line number Diff line change
Expand Up @@ -302,12 +302,12 @@ Total number of `ROL` instructions: `5`.
|------------|---------------------|------------------|-----------|------------|--------------------|
| CMP | Immediate | 0xC9 | 2 | 2 | :white_check_mark: |
| CMP | Zero Page | 0xC5 | 2 | 3 | :white_check_mark: |
| CMP | Zero Page, X | 0xD5 | 2 | 4 | :x: |
| CMP | Absolute | 0xCD | 3 | 4 | :x: |
| CMP | Absolute, X | 0xDD | 3 | 4* | :x: |
| CMP | Absolute, Y | 0xD9 | 3 | 4* | :x: |
| CMP | (Indirect, X) | 0xC1 | 2 | 6 | :x: |
| CMP | (Indirect), Y | 0xD1 | 2 | 5* | :x: |
| CMP | Zero Page, X | 0xD5 | 2 | 4 | :ok: |
| CMP | Absolute | 0xCD | 3 | 4 | :ok: |
| CMP | Absolute, X | 0xDD | 3 | 4* | :ok: |
| CMP | Absolute, Y | 0xD9 | 3 | 4* | :ok: |
| CMP | (Indirect, X) | 0xC1 | 2 | 6 | :ok: |
| CMP | (Indirect), Y | 0xD1 | 2 | 5* | :ok: |

Total number of `CMP` instructions: `8`.

Expand All @@ -317,7 +317,7 @@ Total number of `CMP` instructions: `8`.
|------------|---------------------|------------------|-----------|------------|--------------------|
| CPX | Immediate | 0xE0 | 2 | 2 | :white_check_mark: |
| CPX | Zero Page | 0xE4 | 2 | 3 | :white_check_mark: |
| CPX | Absolute | 0xEC | 3 | 4 | :x: |
| CPX | Absolute | 0xEC | 3 | 4 | :ok: |

Total number of `CPX` instructions: `3`.

Expand All @@ -327,7 +327,7 @@ Total number of `CPX` instructions: `3`.
|------------|---------------------|------------------|-----------|------------|--------------------|
| CPY | Immediate | 0xC0 | 2 | 2 | :white_check_mark: |
| CPY | Zero Page | 0xC4 | 2 | 3 | :white_check_mark: |
| CPY | Absolute | 0xCC | 3 | 4 | :x: |
| CPY | Absolute | 0xCC | 3 | 4 | :ok: |

Total number of `CPY` instructions: `3`.

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116 changes: 99 additions & 17 deletions emulator/emulator.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -1089,6 +1089,14 @@ std::optional<InstructionConfig> sta_index_indirect(emulator::Cpu& cpu, std::spa
}

// Compare instructions here
void cmp_operation(emulator::Cpu& cpu, std::uint8_t emulator::Registers::*reg, std::uint8_t val)
{
auto const comparison = (cpu.reg).*reg - val;
cpu.flags.n = comparison & 0b1000'0000; // Negative flag
cpu.flags.z = comparison == 0; // Negative flag
cpu.flags.c = (cpu.reg).*reg >= val;
}


/// Compares whichever register was given to the immediate
/// value in the next address in the program array
Expand All @@ -1102,12 +1110,7 @@ Instruction cmp_immediate_reg(std::uint8_t emulator::Registers::*reg)
return std::nullopt;
}

auto const value = program[cpu.reg.pc + 1];
auto const comparison = (cpu.reg).*reg - value;
cpu.flags.n = comparison & 0b1000'0000; // Negative flag
cpu.flags.z = comparison == 0; // Negative flag
cpu.flags.c = (cpu.reg).*reg >= value;

cmp_operation(cpu, reg, program[cpu.reg.pc + 1]);
return std::make_optional<InstructionConfig>(2);
};
}
Expand All @@ -1123,17 +1126,91 @@ Instruction cmp_zeropage_reg(std::uint8_t emulator::Registers::*reg)
return std::nullopt;
}

auto const memory = program[cpu.reg.pc + 1];
auto const value = cpu.mem[memory];
auto const comparison = (cpu.reg).*reg - value;
cpu.flags.n = comparison & 0b1000'0000; // Negative flag
cpu.flags.z = comparison == 0; // Negative flag
cpu.flags.n = (cpu.reg).*reg >= value;

auto const memory = program[cpu.reg.pc + 1];
cmp_operation(cpu, reg, cpu.mem[memory]);
return std::make_optional<InstructionConfig>(2);
};
}

std::optional<InstructionConfig> cmp_zp_indexed(emulator::Cpu& cpu, std::span<const std::uint8_t> program)
{
ENABLE_PROFILER(cpu);
if ((cpu.reg.pc + 1) >= program.size())
{
return std::nullopt;
}

auto const pos = zeropage_indexed(cpu, cpu.mem[cpu.reg.pc + 1], &emulator::Registers::x);
cmp_operation(cpu, &emulator::Registers::a, cpu.mem[pos]);
return std::make_optional<InstructionConfig>(2, 4);
}

Instruction cmp_absolute(std::uint8_t emulator::Registers::*reg)
{
return [=](emulator::Cpu& cpu, std::span<const std::uint8_t> program) -> std::optional<InstructionConfig>
{
ENABLE_PROFILER(cpu);
if ((cpu.reg.pc + 2) >= program.size())
{
return std::nullopt;
}

// (hsb << 8) + lsb convert little endian to the address
auto const lsb = program[cpu.reg.pc + 1];
auto const hsb = program[cpu.reg.pc + 2];
auto const addr = static_cast<std::uint16_t>((hsb << 8) | lsb);
auto const memory = program[addr];

cmp_operation(cpu, reg, cpu.mem[memory]);
return std::make_optional<InstructionConfig>(3, 4);
};
}

Instruction cmp_abs_indexed(std::uint8_t emulator::Registers::*index)
{
return [=](emulator::Cpu& cpu, std::span<const std::uint8_t> program) -> std::optional<InstructionConfig>
{
ENABLE_PROFILER(cpu);
if ((cpu.reg.pc + 2) >= program.size())
{
return std::nullopt;
}

auto const pos = absolute_indexed(cpu, program[cpu.reg.pc + 1], program[cpu.reg.pc + 2], index);
cmp_operation(cpu, &emulator::Registers::a, cpu.mem[pos]);

// TODO : Cycle add should reflect the boundary checks
std::size_t const cycle_add = 0;
return std::make_optional<InstructionConfig>(3, 4 + cycle_add);
};
}

std::optional<InstructionConfig> cmp_indexed_indirect(emulator::Cpu& cpu, std::span<std::uint8_t const> program)
{
ENABLE_PROFILER(cpu);
if ((cpu.reg.pc + 1) >= program.size())
{
return std::nullopt;
}

auto const pos = indexed_indirect(cpu, cpu.mem[cpu.reg.pc + 1]);
cmp_operation(cpu, &emulator::Registers::a, cpu.mem[pos]);
return std::make_optional<InstructionConfig>(2, 6);
}

std::optional<InstructionConfig> cmp_indirect_indexed(emulator::Cpu& cpu, std::span<std::uint8_t const> program)
{
ENABLE_PROFILER(cpu);
if ((cpu.reg.pc + 1) >= program.size())
{
return std::nullopt;
}

auto const pos = indirect_indexed(cpu, cpu.mem[cpu.reg.pc + 1]);
cmp_operation(cpu, &emulator::Registers::a, cpu.mem[pos]);
return std::make_optional<InstructionConfig>(2, 6);
}

// Branching functions here
std::optional<InstructionConfig> bne(emulator::Cpu& cpu, std::span<const std::uint8_t> program)
{
Expand Down Expand Up @@ -1547,15 +1624,21 @@ std::array<Instruction, 256> get_instructions()
supported_instructions[0xbc] = ld_absolute_plus_reg(&emulator::Registers::y, &emulator::Registers::x);
supported_instructions[0xac] = ld_absolute(&emulator::Registers::y);

// This is the immediate mode compares to registers
// CMP, CPX, CPY opcodes
supported_instructions[0xc9] = cmp_immediate_reg(&emulator::Registers::a); // TODO : test
supported_instructions[0xc0] = cmp_immediate_reg(&emulator::Registers::y);
supported_instructions[0xe0] = cmp_immediate_reg(&emulator::Registers::x);

// TODO : support for compare zeropage simple
supported_instructions[0xc5] = cmp_zeropage_reg(&emulator::Registers::a);
supported_instructions[0xe4] = cmp_zeropage_reg(&emulator::Registers::x); // TODO : test
supported_instructions[0xc4] = cmp_zeropage_reg(&emulator::Registers::y); // TODO : test
supported_instructions[0xcd] = cmp_absolute(&emulator::Registers::a);
supported_instructions[0xec] = cmp_absolute(&emulator::Registers::x);
supported_instructions[0xcc] = cmp_absolute(&emulator::Registers::y);
supported_instructions[0xd5] = cmp_zp_indexed;
supported_instructions[0xdd] = cmp_abs_indexed(&emulator::Registers::x);
supported_instructions[0xd9] = cmp_abs_indexed(&emulator::Registers::y);
supported_instructions[0xc1] = cmp_indexed_indirect;
supported_instructions[0xd1] = cmp_indirect_indexed;

supported_instructions[0xf0] = branch_flag_value<true>(&emulator::Flags::z);
supported_instructions[0xd0] = branch_flag_value<false>(&emulator::Flags::z);
Expand Down Expand Up @@ -1689,7 +1772,6 @@ std::optional<InstructionConfig> execute_next(

export namespace emulator
{

std::size_t execute(Cpu& cpu, std::span<const std::uint8_t> program)
{
std::size_t n_cycles = 0;
Expand Down

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