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:
- Z80NMOS - A Zilog’s NMOS Z80.
- Z80CMOS - A CMOS version of Z80.
- z80::Z80BM1 - A clone of Z80.
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.
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 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 directory and the shuffle example. 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.
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
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;
pub use z80::any::Z80Any;
Modules
Structs
Enums
Constants
Traits
self
at User’s will.Type Definitions
debug
argument.