[−][src]Crate z80emu

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.

For an emulator to be complete, 4 traits need to be implemented.

The traits:

Cpu - An interface to the finite state machine that is able to "execute" the machine code instructions as one of the Z80 family processors. Interacting with the memory or I/O devices as well as synchronizing the execution via T-states counting is realized via the following traits.
Clock - A Cpu T-state cycle counter which can be used to synchronize the Cpu emulation with the emulator's side effects.
Memory - The Cpu interacts with the memory via this trait.
Io - The Cpu uses this for I/O and maskable interrupts.

z80emu crate provides 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 each trait's documentation on how to implement them.

In this crate one implementation of the Cpu trait is provided with some selectable "flavours":

Z80NMOS - A Zilog's NMOS Z80.
Z80CMOS - A CMOS version of Z80.
z80::Z80BM - A clone of Z80.

The difference is very subtle and only affects the undocumented behaviour.

Debugger

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 e.g. display human readable text of the disassembled instructions or gather statistics.

In z80emu the command execution code and the debugger code is 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 is able to 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 complete customized debugging solution.

How To

Start by inspecting the tests and benches directory. All of the test cases run a minimalistic Z80 virtual computers and can be usefull in learning about 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. This is of course not the only way one can implement that, but perhaps it can give some ideas.

Example

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

fn main() {
  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);
}

Re-exports

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;

Modules

host	This module contains traits that should be implemented by the user.
opconsts	Some of the selected Z80 op-codes for providing to the Cpu::execute_instruction or returning from Io::irq_data.
z80	A home of the Cpu implementations.

Structs

CpuDebug	This struct is being passed to the user debugger function when the command is being executed.
CpuFlags	A type representing Z80 Cpu Flag register's content.
RegisterPair	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.

Enums

Condition
CpuDebugAddr	An address command argument.
CpuDebugArg	An enum holding a single command argument.
CpuDebugArgs	An enum holding the command arguments.
CpuDebugPort	An I/O port address.
InterruptMode	The interrupt mode enum.
Prefix	A prefix enum that modifies behaviour of the next op-code.
Reg8
Reg16
StkReg16

Constants

NMI_RESTART

An address of the NMI routine.

Traits

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

Type Definitions

CpuDebugCode	The type that stores a copy of the instruction's full byte code.
CpuDebugFn	The type that can be passed to methods of the Cpu that require a `debug` argument.