k580-core 2.0.0

KR580VM80 / Intel 8080 CPU core for KR580.
Documentation 
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use k580_core::{Cpu8080State, NullBus};

fn put_program(cpu: &mut Cpu8080State, bytes: &[u8]) {
    for (offset, byte) in bytes.iter().copied().enumerate() {
        cpu.memory.write(offset as u16, byte);
    }
}

fn step_tacts(cpu: &mut Cpu8080State, bus: &mut NullBus, count: u8) {
    for _ in 0..count {
        cpu.step_tact(bus).unwrap();
    }
}

#[test]
fn step_tact_defers_nop_until_instruction_boundary() {
    let mut cpu = Cpu8080State::default();
    put_program(&mut cpu, &[0x00]);
    let mut bus = NullBus::default();

    let first = cpu.step_tact(&mut bus).unwrap();
    assert_eq!(first.tact_phase, 0);
    assert!(!first.instruction_boundary);
    assert_eq!(cpu.pc, 0);
    assert_eq!(cpu.cycle_count, 1);

    step_tacts(&mut cpu, &mut bus, 2);
    assert_eq!(cpu.pc, 0);
    assert_eq!(cpu.tact_phase, Some(3));

    let last = cpu.step_tact(&mut bus).unwrap();
    assert_eq!(last.tact_phase, 3);
    assert!(last.instruction_boundary);
    assert_eq!(cpu.pc, 1);
    assert_eq!(cpu.tact_phase, None);
}

#[test]
fn step_tact_delays_port_output_until_final_tact() {
    let mut cpu = Cpu8080State::default();
    put_program(&mut cpu, &[0xD3, 0x04]);
    cpu.registers.a = 0x77;
    let mut bus = NullBus::default();

    step_tacts(&mut cpu, &mut bus, 9);
    assert_eq!(cpu.pc, 0);
    assert!(bus.writes().is_empty());

    let last = cpu.step_tact(&mut bus).unwrap();
    assert!(last.instruction_boundary);
    assert_eq!(cpu.pc, 2);
    assert_eq!(bus.writes(), &[(0x04, 0x77)]);
}

#[test]
fn step_instruction_completes_active_tact_walk_once() {
    let mut atomic = Cpu8080State::default();
    put_program(&mut atomic, &[0xD3, 0x04]);
    atomic.registers.a = 0x77;
    let mut atomic_bus = NullBus::default();
    atomic.step_instruction(&mut atomic_bus).unwrap();

    let mut mixed = Cpu8080State::default();
    put_program(&mut mixed, &[0xD3, 0x04]);
    mixed.registers.a = 0x77;
    let mut mixed_bus = NullBus::default();

    step_tacts(&mut mixed, &mut mixed_bus, 4);
    assert_eq!(mixed.pc, 0);
    assert!(mixed_bus.writes().is_empty());

    mixed.step_instruction(&mut mixed_bus).unwrap();
    assert_eq!(mixed, atomic);
    assert_eq!(mixed_bus.writes(), atomic_bus.writes());
}

#[test]
fn interrupt_tact_walk_matches_step_instruction() {
    let mut atomic = Cpu8080State::default();
    atomic.sp = 0x9000;
    atomic.pc = 0x1234;
    atomic.interrupt_enable = true;
    atomic.request_interrupt(0xCF);
    atomic.step_instruction(&mut NullBus::default()).unwrap();

    let mut walked = Cpu8080State::default();
    walked.sp = 0x9000;
    walked.pc = 0x1234;
    walked.interrupt_enable = true;
    walked.request_interrupt(0xCF);
    step_tacts(&mut walked, &mut NullBus::default(), 11);

    assert_eq!(walked, atomic);
}

#[test]
fn full_tact_walk_matches_step_instruction_for_representative_opcodes() {
    let programs: &[(&[u8], u8)] = &[
        (&[0x00], 4),
        (&[0x01, 0x34, 0x12], 10),
        (&[0x32, 0x00, 0x20], 13),
        (&[0xD3, 0x04], 10),
        (&[0xDB, 0x03], 10),
        (&[0xCD, 0x00, 0x10], 17),
        (&[0x76], 7),
    ];

    for &(program, t_states) in programs {
        let mut atomic = Cpu8080State::default();
        put_program(&mut atomic, program);
        atomic.sp = 0x9000;
        atomic.registers.a = 0x66;
        let mut atomic_bus = NullBus::default();
        atomic_bus.set_input(0x03, 0xA5);
        atomic.step_instruction(&mut atomic_bus).unwrap();

        let mut walked = Cpu8080State::default();
        put_program(&mut walked, program);
        walked.sp = 0x9000;
        walked.registers.a = 0x66;
        let mut walked_bus = NullBus::default();
        walked_bus.set_input(0x03, 0xA5);
        step_tacts(&mut walked, &mut walked_bus, t_states);

        assert_eq!(walked, atomic, "program {program:02X?}");
        assert_eq!(
            walked_bus.writes(),
            atomic_bus.writes(),
            "program {program:02X?}"
        );
    }
}

#[test]
fn conditional_call_tact_count_follows_branch_state() {
    let mut cpu = Cpu8080State::default();
    put_program(&mut cpu, &[0xCC, 0x00, 0x10]);
    cpu.flags.zero = false;
    let mut bus = NullBus::default();

    step_tacts(&mut cpu, &mut bus, 10);
    assert_eq!(cpu.pc, 0);
    assert_eq!(cpu.tact_phase, Some(10));

    let last = cpu.step_tact(&mut bus).unwrap();
    assert!(last.instruction_boundary);
    assert_eq!(cpu.pc, 3);

    let mut taken = Cpu8080State::default();
    put_program(&mut taken, &[0xCC, 0x00, 0x10]);
    taken.sp = 0x9000;
    taken.flags.zero = true;
    let mut bus = NullBus::default();

    step_tacts(&mut taken, &mut bus, 16);
    assert_eq!(taken.pc, 0);
    assert_eq!(taken.tact_phase, Some(16));

    let last = taken.step_tact(&mut bus).unwrap();
    assert!(last.instruction_boundary);
    assert_eq!(taken.pc, 0x1000);
}