Merge 38a2dfb2f3 into 4847744518

src/cpu.rs

@@ -31,10 +31,8 @@ use crate::Variant;
 
 use crate::registers::{Registers, StackPointer, Status, StatusArgs};
 
-fn arr_to_addr(arr: &[u8]) -> u16 {
-    debug_assert!(arr.len() == 2);
-
-    u16::from(arr[0]) + (u16::from(arr[1]) << 8usize)
+fn address_from_bytes(lo: u8, hi: u8) -> u16 {
+    u16::from(lo) + (u16::from(hi) << 8usize)
 }
 
 #[derive(Clone)]
@@ -136,24 +134,52 @@ impl<M: Bus, V: Variant> CPU<M, V> {
                     AddressingMode::Absolute => {
                         // Use [u8, ..2] from instruction as address
                         // (Output: a 16-bit address)
-                        OpInput::UseAddress(arr_to_addr(&slice))
+                        OpInput::UseAddress(address_from_bytes(slice[0], slice[1]))
                     }
                     AddressingMode::AbsoluteX => {
                         // Use [u8, ..2] from instruction as address, add X
                         // (Output: a 16-bit address)
-                        OpInput::UseAddress(arr_to_addr(&slice).wrapping_add(x.into()))
+                        OpInput::UseAddress(
+                            address_from_bytes(slice[0], slice[1]).wrapping_add(x.into()),
+                        )
                     }
                     AddressingMode::AbsoluteY => {
                         // Use [u8, ..2] from instruction as address, add Y
                         // (Output: a 16-bit address)
-                        OpInput::UseAddress(arr_to_addr(&slice).wrapping_add(y.into()))
+                        OpInput::UseAddress(
+                            address_from_bytes(slice[0], slice[1]).wrapping_add(y.into()),
+                        )
                     }
                     AddressingMode::Indirect => {
                         // Use [u8, ..2] from instruction as an address. Interpret the
                         // two bytes starting at that address as an address.
                         // (Output: a 16-bit address)
-                        let slice = read_address(memory, arr_to_addr(&slice));
-                        OpInput::UseAddress(arr_to_addr(&slice))
+                        // TODO: If the pointer ends in 0xff, then incrementing it would propagate
+                        // the carry to the high byte of the pointer. This incurs a cost of one
+                        // machine cycle on the real 65C02, which is not implemented here.
+                        let slice = read_address(memory, address_from_bytes(slice[0], slice[1]));
+                        OpInput::UseAddress(address_from_bytes(slice[0], slice[1]))
+                    }
+                    AddressingMode::BuggyIndirect => {
+                        // Use [u8, ..2] from instruction as an address. Interpret the
+                        // two bytes starting at that address as an address.
+                        // (Output: a 16-bit address)
+                        let pointer = address_from_bytes(slice[0], slice[1]);
+
+                        let low_byte_of_target = memory.get_byte(pointer);
+
+                        let low_byte_of_incremented_pointer =
+                            pointer.to_le_bytes()[0].wrapping_add(1);
+                        let incremented_pointer = u16::from_le_bytes([
+                            low_byte_of_incremented_pointer,
+                            pointer.to_le_bytes()[1],
+                        ]);
+
+                        let high_byte_of_target = memory.get_byte(incremented_pointer);
+                        OpInput::UseAddress(address_from_bytes(
+                            low_byte_of_target,
+                            high_byte_of_target,
+                        ))
                     }
                     AddressingMode::IndexedIndirectX => {
                         // Use [u8, ..1] from instruction
@@ -162,7 +188,7 @@ impl<M: Bus, V: Variant> CPU<M, V> {
                         // (Output: a 16-bit address)
                         let start = slice[0].wrapping_add(x);
                         let slice = read_address(memory, u16::from(start));
-                        OpInput::UseAddress(arr_to_addr(&slice))
+                        OpInput::UseAddress(address_from_bytes(slice[0], slice[1]))
                     }
                     AddressingMode::IndirectIndexedY => {
                         // Use [u8, ..1] from instruction
@@ -171,7 +197,9 @@ impl<M: Bus, V: Variant> CPU<M, V> {
                         // (Output: a 16-bit address)
                         let start = slice[0];
                         let slice = read_address(memory, u16::from(start));
-                        OpInput::UseAddress(arr_to_addr(&slice).wrapping_add(y.into()))
+                        OpInput::UseAddress(
+                            address_from_bytes(slice[0], slice[1]).wrapping_add(y.into()),
+                        )
                     }
                 };
 
@@ -1103,6 +1131,28 @@ mod tests {
         assert_eq!(cpu.registers.accumulator, 0);
     }
 
+    #[cfg_attr(feature = "decimal_mode", test)]
+    fn invalid_decimal_values_test() {
+        let mut cpu = CPU::new();
+        cpu.registers.status.remove(Status::PS_CARRY);
+
+        cpu.add_with_carry(0x0e);
+        assert_eq!(cpu.registers.accumulator, 0x0e);
+        cpu.registers.status.or(Status::PS_DECIMAL_MODE);
+        assert_eq!(cpu.registers.accumulator, 0x0e);
+        assert!(!cpu.registers.status.contains(Status::PS_CARRY));
+        assert!(!cpu.registers.status.contains(Status::PS_ZERO));
+        assert!(!cpu.registers.status.contains(Status::PS_NEGATIVE));
+        assert!(!cpu.registers.status.contains(Status::PS_OVERFLOW));
+
+        cpu.add_with_carry(-92); // hex $a4
+        assert_eq!(cpu.registers.accumulator, 0x18);
+        assert!(cpu.registers.status.contains(Status::PS_CARRY));
+        assert!(!cpu.registers.status.contains(Status::PS_ZERO));
+        assert!(cpu.registers.status.contains(Status::PS_NEGATIVE));
+        assert!(!cpu.registers.status.contains(Status::PS_OVERFLOW));
+    }
+
     #[cfg_attr(feature = "decimal_mode", test)]
     fn decimal_add_test() {
         let mut cpu = CPU::new(Ram::new(), Nmos6502);

src/instruction.rs

@@ -117,21 +117,47 @@ pub enum OpInput {
 
 #[derive(Copy, Clone)]
 pub enum AddressingMode {
-    Accumulator,      // 1    LSR A        work directly on accumulator
-    Implied,          // 1    BRK
-    Immediate,        // 2    LDA #10      8-bit constant in instruction
-    ZeroPage,         // 2    LDA $00      zero-page address
-    ZeroPageX,        // 2    LDA $80,X    address is X register + 8-bit constant
-    ZeroPageY,        // 2    LDX $10,Y    address is Y register + 8-bit constant
-    Relative,         // 2    BNE LABEL    branch target as signed relative offset
-    Absolute,         // 3    JMP $1000    full 16-bit address
-    AbsoluteX,        // 3    STA $1000,X  full 16-bit address plus X register
-    AbsoluteY,        // 3    STA $1000,Y  full 16-bit address plus Y register
-    Indirect,         // 3    JMP ($1000)  jump to address stored at address
-    IndexedIndirectX, // 2    LDA ($10,X)  load from address stored at (constant
-    //                   zero page address plus X register)
-    IndirectIndexedY, // 2    LDA ($10),Y  load from (address stored at constant
-                      //                   zero page address) plus Y register
+    // work directly on accumulator, e. g. `lsr a`.
+    Accumulator,
+
+    // BRK
+    Implied,
+
+    // 8-bit constant in instruction, e. g. `lda #10`.
+    Immediate,
+
+    // zero-page address, e. g. `lda $00`.
+    ZeroPage,
+
+    // address is X register + 8-bit constant, e. g. `lda $80,x`.
+    ZeroPageX,
+
+    // address is Y register + 8-bit constant, e. g. `ldx $10,y`.
+    ZeroPageY,
+
+    // branch target as signed relative offset, e. g. `bne label`.
+    Relative,
+
+    // full 16-bit address, e. g. `jmp $1000`.
+    Absolute,
+
+    // full 16-bit address plus X register, e. g. `sta $1000,X`.
+    AbsoluteX,
+
+    // full 16-bit address plus Y register, e. g. `sta $1000,Y`.
+    AbsoluteY,
+
+    // jump to address stored at address, with the page-crossing bug found in NMOS chips, e. g. `jmp ($1000)`.
+    BuggyIndirect,
+
+    // jump to address stored at address, e. g. `jmp ($1000)`.
+    Indirect,
+
+    // load from address stored at (constant zero page address plus X register), e. g. `lda ($10,X)`.
+    IndexedIndirectX,
+
+    // load from (address stored at constant zero page address) plus Y register, e. g. `lda ($10),Y`.
+    IndirectIndexedY,
 }
 
 impl AddressingMode {
@@ -148,6 +174,7 @@ impl AddressingMode {
             AddressingMode::AbsoluteX => 2,
             AddressingMode::AbsoluteY => 2,
             AddressingMode::Indirect => 2,
+            AddressingMode::BuggyIndirect => 2,
             AddressingMode::IndexedIndirectX => 1,
             AddressingMode::IndirectIndexedY => 1,
         }
@@ -270,7 +297,7 @@ impl crate::Variant for Nmos6502 {
             0x69 => Some((Instruction::ADC, AddressingMode::Immediate)),
             0x6a => Some((Instruction::ROR, AddressingMode::Accumulator)),
             0x6b => None,
-            0x6c => Some((Instruction::JMP, AddressingMode::Indirect)),
+            0x6c => Some((Instruction::JMP, AddressingMode::BuggyIndirect)),
             0x6d => Some((Instruction::ADC, AddressingMode::Absolute)),
             0x6e => Some((Instruction::ROR, AddressingMode::Absolute)),
             0x6f => None,
@@ -466,3 +493,16 @@ impl crate::Variant for RevisionA {
         }
     }
 }
+
+/// Emulates the 65C02, which has a few bugfixes, and another addressing mode
+pub struct Cmos6502;
+
+impl crate::Variant for Cmos6502 {
+    fn decode(opcode: u8) -> Option<(Instruction, AddressingMode)> {
+        // TODO: We obviously need to add the other CMOS instructions here.
+        match opcode {
+            0x6c => Some((Instruction::JMP, AddressingMode::Indirect)),
+            _ => Nmos6502::decode(opcode),
+        }
+    }
+}