initial commit

cpu.cpp

@@ -0,0 +1,129 @@
+#include "cpu.h"
+
+CPU::CPU(IMemoryAccessor* memory) : a(0), x(0), y(0), pc(0), sp(0), stat(0), cycles(0)
+{
+    _memory = memory;
+}
+
+void CPU::start()
+{
+    a = 0;
+    x = 0;
+    y = 0;
+    sp = 0xFF;
+    pc = 0xFFFC;
+}
+
+void CPU::reset()
+{
+    pc = 0xFFFC;
+    sp -= 3;
+}
+
+void CPU::loop()
+{
+    bool stop = false;
+    while (!stop)
+    {
+        const std::uint8_t op = _memory->read8(pc++);
+        switch (static_cast<int>(op))
+        {
+        case 0x69:
+        case 0x65:
+        case 0x75:
+        case 0x6D:
+            adc(op);
+            break;
+        default:
+            stop = true;
+            break;
+        }
+    }
+}
+
+std::uint8_t CPU::readImm() const
+{
+    return _memory->read8(pc);
+}
+
+std::uint8_t CPU::readZp() const
+{
+    const std::uint8_t zpOffset = _memory->read8(pc);
+    return _memory->read8(0x0000 + zpOffset);
+}
+
+std::uint8_t CPU::readZpX() const
+{
+    const std::uint8_t zpOffset = _memory->read8(pc);
+    const uint16_t eff = 0x0000 + zpOffset + x & 0x00FF;
+    return _memory->read8(eff);
+}
+
+std::uint8_t CPU::readAbs()
+{
+    const std::uint8_t low = _memory->read8(pc++);
+    const std::uint8_t high = _memory->read8(pc);
+    const uint16_t eff = static_cast<uint16_t>(high) << 8 | low;
+    return _memory->read8(eff);
+}
+
+std::uint8_t CPU::readAbsX()
+{
+    const std::uint8_t low = _memory->read8(pc++);
+    const std::uint8_t high = _memory->read8(pc);
+    const uint16_t eff = (static_cast<uint16_t>(high) << 8 | low) + x;
+    return _memory->read8(eff);
+}
+
+std::uint8_t CPU::readAbsY()
+{
+    const std::uint8_t low = _memory->read8(pc++);
+    const std::uint8_t high = _memory->read8(pc);
+    const uint16_t eff = (static_cast<uint16_t>(high) << 8 | low) + y;
+    return _memory->read8(eff);
+}
+
+std::uint8_t CPU::readIdxInd()
+{
+
+}
+
+std::uint8_t CPU::readIndIdx()
+{
+
+}
+
+void CPU::adc(std::uint8_t opcode)
+{
+    uint8_t val;
+    switch (static_cast<int>(opcode))
+    {
+    case 0x69:
+        val = readImm();
+        break;
+    case 0x65:
+        val = readZp();
+        break;
+    case 0x75:
+        val = readZpX();
+        break;
+    case 0x6D:
+        val = readAbs();
+        break;
+    default:
+        stop = true;
+        return;
+    }
+
+    const uint16_t result = a + val + static_cast<std::uint8_t>(c());
+    a = result & 0xFF;
+    setFlagsFromResult(result);
+}
+
+void CPU::setFlagsFromResult(std::uint16_t result)
+{
+    if (result > 0xFF)  // unsigned overflow
+    {
+        c(true);
+    }
+}