Crate z80emu[][src]

Expand description

Z80 emu

z80emu crate provides building blocks for emulators based on Zilog’s Z80 CPU family.

To build the crate with no_std support make sure to set default-features to false and select the required features only.

=|       |=
=|       |=
=|       |= ---------------- =[   Clock   ]
=|       |=                         |
=|       |=                         |
=|       |=                         |
=|       |=                         |
=|       |=                         |
=|  Cpu  |=                    _____|_____
=|       |=                   |           |
=|  Z80  |= \                 |           |
=|       |= <--------------> =| Memory+Io |=:::::
=|       |= /                 |           |
=|       |=                   |___________|
=|       |=
=|       |=
=|       |=
=|       |=
=|       |=

z80emu was developed as an attempt to create a minimalistic emulation library. It provides the necessary tools for the retro emulators to be built upon, avoiding any assumptions about side effects of those emulators.

The idea is to leverage the Rust’s trait based OO model for this purpose.

There are four important traits in this library - the essential components of an emulated computer:

  • Cpu - an interface to the finite state machine that can alter its state by executing the machine code instructions as one of the Z80 family processors.
  • Clock - an interface to the CPU cycle (T-state) counter, which can be used to synchronize the emulation with the emulator’s side effects.
  • Memory - an interface to the host’s memory that the Cpu is using to read from and write to it.
  • Io - an interface to the host’s I/O devices that the Cpu is using to access them.

z80emu crate provides the Cpu trait implementations and an example implementation for the Clock trait. The rest of the traits need to be implemented by the emulator’s developer. Please see the documentation of this module for more information on how to implement them.

The Z80 struct implements the Cpu trait with a selectable Flavour as its generic parameter.

Currently, there are 3 “flavour” implementations for which the following CPU types are available:

The difference between each of them is very subtle and only affects undocumented behavior. Alternatively, a Z80Any enum can be used if changing of the z80::Flavour in run time is required.


The Cpu trait provides an ability to debug the executed machine code. Some of the Cpu functions accept the optional callback argument: debug. This callback is being fed with the extended information about the command being executed, and can be used to display the human-readable text of the disassembled instructions or gather statistics.

In z80emu the command execution code and the debugger code are implemented together in a single unit. This way there is only a single machine code dispatcher. This minimizes the probability of a debugger suffering from “schizophrenic effects” showing results not compatible with the execution unit. Thanks to Rust and LLVM, the compilator can optimize out the debugger parts when they are not needed.

The debugger provides information as a CpuDebug struct. It implements Display, LowerHex, and UpperHex traits so it’s easy to print it OOB as well as provide a complete customized debugging solution.

How To

Start by inspecting the tests and benches directory. All of the test cases run minimalistic Z80 virtual computers and can be useful in learning the essentials.

For a bigger picture see the crate’s repository example implementation of the imaginary Z80 based computer, to see how a system bus could be implemented with custom PIO and CTC peripheral chips.


use z80emu::*;
use opconsts::HALT_OPCODE;
// Let's use the simple T-state counter.
type TsClock = host::TsCounter<i32>;

// Let's add some memory.
#[derive(Clone, Debug, Default)]
struct Bus {
    rom: [u8;11]

impl Io for Bus {
    type Timestamp = i32;
    type WrIoBreak = ();
    type RetiBreak = ();

impl Memory for Bus {
    type Timestamp = i32;
    fn read_debug(&self, addr: u16) -> u8 {
        self.rom[addr as usize]

const FIB_N: u8 = 24; // 1..=24

let mut tsc = TsClock::default();
let mut fibbo = Bus { rom: [
    0x21, 0x00, 0x00, // 0x0000 LD   HL, 0x0000
    0x11, 0x01, 0x00, // 0x0003 LD   DE, 0x0001
    0xEB,             // 0x0006 EX   DE, HL
    0x19,             // 0x0007 ADD  HL, DE
    0x10, 0xFC,       // 0x0008 DJNZ 0x0006
    HALT_OPCODE       // 0x000A HALT
] };
let mut cpu = Z80NMOS::default();
cpu.reset(); // PC = 0
cpu.set_reg(Reg8::B, None, FIB_N); // Cpu register B = FIB_N
// Let's calculate a Fibbonacci number
loop {
    match cpu.execute_next(&mut fibbo, &mut tsc,
            Some(|deb| println!("{:#X}", deb) )) {
        Err(BreakCause::Halt) => { break }
        _ => {}
// the content of the HL registers
let result = cpu.get_reg16(StkReg16::HL);
assert_eq!(result, 46368); // Fib(24)
// the number of T-states passed
assert_eq!(tsc.as_timestamp(), 10+10+(FIB_N as i32)*(4+11+13)-5+4);


pub use host::Clock;
pub use host::Io;
pub use host::Memory;
pub use host::BreakCause;
pub use z80::Z80;
pub use z80::Z80NMOS;
pub use z80::Z80CMOS;
pub use z80::any::Z80Any;


Utilities for disassembling Z80 machine code.

This module contains traits that should be implemented by the builder of the host computer.

Selected Z80 opcodes.

A home of the Cpu implementations.


This struct is being passed to the user debugger function when the command is being executed.

Z80 Cpu Flags.

A struct that represents a register pair, that can be treated as a single 16-bit register or a separate 8-bit (MSB/LSB) registers.


An address command argument.

A command argument.

An enum holding the command arguments.

An I/O port address.

An enum representing the maskable interrupt modes.

An enum that indicates how the next executed op-code will be modified.


An address of the NMI routine.


The Cpu trait provides means to execute and debug machine code or change the state of self at User’s will.

Type Definitions

The type that stores a copy of the instruction’s full byte code.

This type can be passed to Cpu methods that require a debug argument.