- Borrador de microcodi per a versió alternativa del 6502

2025-02-04 14:01:07 +01:00
parent fb2c69c6a4
commit 57e91fbdef
1 changed files with 198 additions and 0 deletions
--- a/microcode.txt
+++ b/microcode.txt
@@ -0,0 +1,198 @@
+LDA LDX LDY BIT ADC SBC AND ORA EOR CMP CPX CPY
+=====================================
+
+LDA #imm
+    FetchOperandLo
+    FetchOpcode
+
+LDA ZeroPage
+    FetchOperandLo
+    ReadAddress
+    FetchOpcode
+
+LDA ZeroPage,X
+    FetchOperandLo
+    IndexX
+    ReadAddress;
+    FetchOpcode
+
+LDA Absolute
+    FetchOperandLo
+    FetchOperandHi
+    ReadAddress
+    FetchOpcode
+
+LDA Absolute, X/Y
+    FetchOperandLo
+    FetchOperandHiAndIndex;
+    ReadAddressAndSkip;
+    ReadAddress
+    FetchOpcode
+
+LDA (Indirect, X)
+    FetchOperandLo
+    IndexX
+    FetchAddressLo;
+    FetchAddressHi;
+    ReadAddress
+    FetchOpcode
+
+LDA (Indirect), Y
+    FetchOperandLo
+    FetchAddressLo
+    FetchAddressHiAndIndex
+    ReadAddressAndSkip
+    ReadAddress
+    FetchOpcode
+
+
+STA STX STY
+=====================================
+
+STA ZeroPage
+    FetchOperandLo
+    WriteRegister
+    FetchOpcode
+
+STA ZeroPage, X
+    FetchOperandLo
+    IndexX
+    WriteRegister
+    FetchOpcode
+
+STA Absolute
+    FetchOperandLo
+    FetchOperandHi
+    WriteRegister
+    FetchOpcode
+
+STA Absolute, X/Y
+    FetchOperandLo
+    FetchOperandHiAndIndex
+    ReadAddress
+    WriteRegister
+    FetchOpcode
+
+STA (Indirect, X)
+    FetchOperandLo
+    IndexX
+    FetchAddressLo
+    FetchAddressHi
+    WriteRegister
+    FetchOpcode
+
+STA (Indirect), Y
+    FetchOperandLo
+    FetchAddressLo
+    FetchAddressHiAndIndex
+    ReadAddress
+    WriteRegister
+    FetchOpcode
+
+ASL LSR ROL ROR INC DEC
+========================
+ASL A
+    FakeFetchOperand
+    FetchOpcode
+
+ASL ZeroPage
+    FetchOperandLo
+    ReadAddress
+    WriteAddress
+    WriteAddress
+    FetchOpcode
+
+ASL ZeroPage, X
+    FetchOperandLo
+    IndexX
+    ReadAddress
+    WriteAddress
+    WriteAddress
+    FetchOpcode
+
+ASL Absolute
+    FetchOperandLo
+    FetchOperandHi
+    ReadAddress
+    WriteAddress
+    WriteAddress
+    FetchOpcode
+
+ASL Absolute, X
+    FetchOperandLo
+    FetchOperandHiAndIndex
+    ReadAddress
+    ReadAddress
+    WriteAddress
+    WriteAddress
+    FetchOpcode
+
+BCC BCS BNE BEQ BPL BMI BVC BVS
+========================
+BCC
+    FetchOperandLo
+    CheckIfTaken;
+    CheckIfPageCrossed;
+    FetchOpcode
+
+
+
+MICROINSTRUCTIONS
+===========================================
+
+FetchOpcode
+    DoOpcodeWork();
+    IR = Mem::Read(PC++);
+    Decode();
+    ResetState();
+
+FakeFetchOperand
+    Address.Lo = Mem::Read(PC);
+
+FetchOperandLo
+    Address.Lo = B = Mem::Read(PC++);
+
+FetchOperandHi
+    Address.Hi = Mem::Read(PC++);
+
+FetchOperandHiAndIndex
+    Address.Hi = Mem::Read(PC++);
+    if (Address.Lo+X/Y > 255) pageCrossed = true;
+    Address.Lo += X/Y;
+
+ReadAddress
+    B = Mem::Read(Address);
+    if (pageCrossed) Address += 0x0100;
+
+ReadAddressAndSkip
+    B = Mem::Read(Address);
+    if (pageCrossed)
+        Address += 0x0100;
+    else
+        InsertFetchOpcode();
+
+IndexX
+    B = Mem::Read(Address);
+    Address.Lo += X;
+
+FetchAddressLo
+    Add2.Lo = Mem::Read(Address++);
+
+FetchAddressHi
+    Add2.Hi = Mem::Read(Address);
+    Address = Add2;
+
+FetchAddressHiAndIndex
+    Add2.Hi = Mem::Read(Address);
+    if (Add2.lo+Y > 255) pageCrossed = true;
+    Address = Add2;
+
+WriteRegister
+    if ((IR&3)==1) Mem::Write(Address, rA);
+    else if ((IR&3)==2) Mem::Write(Address, rX);
+    else if ((IR&3)==0) Mem::Write(Address, rY);
+
+WriteAddress
+    Mem::Write(Address, B);
+    DoOpcodeWork();
+