Implement jump immediate instruction

src/cpu.rs

@@ -34,6 +34,7 @@ impl Processor {
             parse::next_instruction(&memory_view).expect("invalid instruction");
 
         let interrupt_enable_pending_already = self.interrupt_enable_pending;
+        let pc_before_instruction_run = self.registers.program_counter;
         self.run_instruction(instruction);
 
         // EI does not work until after the following instruction, so we check after running an instruction if
@@ -43,8 +44,12 @@ impl Processor {
             self.registers.enable_interrupts();
         }
 
-        let next_pc = pc.wrapping_add(bytes_read);
-        self.registers.program_counter = next_pc;
+        if pc_before_instruction_run == self.registers.program_counter {
+            // The program counter should be advanced *ONLY* if the instruction did not modify the PC register
+
+            let next_pc = pc.wrapping_add(bytes_read);
+            self.registers.program_counter = next_pc;
+        }
     }
 
     /// Run a single instruction on the CPU.

src/cpu/instructions.rs

@@ -6,6 +6,7 @@ use super::parse::{self, Error};
 
 pub mod arith16;
 pub mod arith8;
+pub mod control;
 pub mod load16;
 pub mod load8;
 pub mod misc;
@@ -19,6 +20,7 @@ pub enum Instruction {
     EightBitArithmetic(arith8::EightBitArithmeticInstruction),
     StackPointerAdjust(arith8::AdjustStackPointerInstruction),
     SixteenBitArithmetic(arith16::SixteenBitArithmeticInstruction),
+    ControlFlow(control::ControlFlowInstruction),
     Misc(misc::MiscInstruction),
 }
 

src/cpu/instructions/control.rs

@@ -0,0 +1,5 @@
+#[allow(clippy::module_name_repetitions)]
+#[derive(Debug, Clone, Copy)]
+pub enum ControlFlowInstruction {
+    JumpToImmediate { addr: u16 },
+}

src/cpu/parse.rs

@@ -7,6 +7,7 @@ use thiserror::Error;
 
 mod arith16;
 mod arith8;
+mod control;
 mod load16;
 mod load8;
 mod misc;
@@ -45,6 +46,7 @@ pub fn next_instruction(data: &View) -> ParseResult {
         load16::stack::Parser::parse_opcode,
         arith8::Parser::parse_opcode,
         arith16::Parser::parse_opcode,
+        control::Parser::parse_opcode,
         misc::Parser::parse_opcode,
     ];
 

src/cpu/parse/control.rs

@@ -0,0 +1,33 @@
+use crate::{
+    cpu::{
+        instructions::{control::ControlFlowInstruction, Instruction},
+        parse,
+    },
+    memory::{GetViewTuple, View},
+};
+
+use super::{OpcodeParser, ParseOutput, ParseResult};
+
+pub struct Parser;
+
+impl OpcodeParser for Parser {
+    fn parse_opcode(data: &View) -> ParseResult {
+        let opcode = parse::get_opcode_from_data(data);
+        match opcode {
+            0xC3 => Ok(build_jump_to_immediate_data(data)),
+            _ => Err(parse::Error::UnknownOpcode(opcode)),
+        }
+    }
+}
+
+fn build_jump_to_immediate_data(data: &View) -> ParseOutput {
+    let (_opcode, lower_bytes, upper_bytes) = data.get_tuple();
+
+    // manual doesn't state this should be LE, but some inspection of games and googling
+    // indicates it should be.
+    let addr = u16::from_le_bytes([lower_bytes, upper_bytes]);
+    (
+        Instruction::ControlFlow(ControlFlowInstruction::JumpToImmediate { addr }),
+        3,
+    )
+}

src/cpu/run.rs

@@ -7,6 +7,7 @@ use thiserror::Error;
 mod arith16;
 mod arith8;
 mod arithutil;
+mod control;
 mod load16;
 mod load8;
 mod misc;
@@ -48,6 +49,7 @@ pub fn run_instruction(
         Instruction::EightBitArithmetic(arith_instruction) => arith_instruction.run_on(processor),
         Instruction::StackPointerAdjust(adjust_instruction) => adjust_instruction.run_on(processor),
         Instruction::SixteenBitArithmetic(arith_instruction) => arith_instruction.run_on(processor),
+        Instruction::ControlFlow(control_instruction) => control_instruction.run_on(processor),
         Instruction::Misc(instruction) => instruction.run_on(processor),
     }
 }

src/cpu/run/control.rs

@@ -0,0 +1,17 @@
+use crate::cpu::{instructions::control::ControlFlowInstruction, register, Processor};
+
+use super::{Cycles, Run};
+
+impl Run for ControlFlowInstruction {
+    fn run_on(&self, processor: &mut Processor) -> Result<Cycles, super::Error> {
+        match *self {
+            Self::JumpToImmediate { addr } => {
+                processor
+                    .registers
+                    .set_single_16bit_register(register::SingleSixteenBit::ProgramCounter, addr);
+
+                Ok(Cycles(16))
+            }
+        }
+    }
+}

tests/cpu/control.rs

@@ -0,0 +1,15 @@
+use ferris_boi::cpu::{instructions::Instruction, Processor};
+
+#[test]
+fn test_can_jump_to_immediate() {
+    let mut processor = Processor::default();
+
+    let data = [0xC3, 0x37, 0x13, 0x06];
+    let (ins, extra_data) = Instruction::from_data(&data).expect("could not parse instruction");
+
+    assert_eq!(extra_data, &[0x06]);
+
+    processor.run_instruction(ins);
+
+    assert_eq!(0x1337, processor.registers.program_counter);
+}

tests/cpu/jsmoo/tests.rs

@@ -73,6 +73,7 @@ fn test_jsmoo_test(filename: &str) {
             processor.registers.l, test_case.r#final.l,
             "register l value was incorrect"
         );
+
         assert_eq!(
             processor.registers.program_counter, test_case.r#final.pc,
             "program counter was incorrect"

tests/cpu/main.rs

@@ -1,5 +1,6 @@
 mod arith16;
 mod arith8;
+mod control;
 mod jsmoo;
 mod load16;
 mod load8;