 An emulator reproducing a console game's playable atmosphere on a Windows computer. A software emulator allows computer programs to run on a platform (computer architecture and/or operating system) other than the one for which they were originally written. Unlike a simulation, which only attempts to reproduce a program's behavior, an emulation generally attempts to model to various degrees the state of the device being emulated. Image File history File links File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ...
Image File history File links File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ...
A console game is a form of interactive multimedia used for entertainment. ...
A computer program or software program (usually abbreviated to a program) is a step-by-step list of instructions written for a particular computer architecture in a particular computer programming language. ...
In computer science, computer architecture is the conceptual design and fundamental operational structure of a computer system. ...
An operating system is a special computer program that manages the relationship between application software, the wide variety of hardware that makes up a computer system, and the user of the system. ...
A simulation is an imitation of some real device or state of affairs. ...
A hardware emulator is a hardware that can run programs for the original hardware without any modification or a hardware that have exactly the same function as the original hardware. Example: Printer Emulator (inside the ROM of the printer), FPGA based emulator. Read-only memory (ROM) is a class of storage media used in computers and other electronic devices. ...
A popular use of emulators is to mimic the experience of running arcade games or console games on Linux, Mac OS X, and Microsoft Windows. Emulating these on modern desktop computers is usually less cumbersome than relying on the original machines. However, software licensing issues may require emulator authors to write original software that duplicates the functionality of the original computer's bootstrap ROM and BIOS, often through high-level emulation. Centipede by Atari is a typical example of a 1980s era arcade game. ...
Tux the penguin, based on an image created by Larry Ewing in 1996, is the logo and mascot of Linux. ...
This article or section does not cite its references or sources. ...
Microsoft Windows is a series of popular proprietary operating environments and operating systems created by Microsoft for use on personal computers and servers. ...
Bootstrapping alludes to a German legend about a Baron Münchhausen, who was able to lift himself out of a swamp by pulling himself up by his bootstraps. ...
Read-only memory (ROM) is a class of storage media used in computers and other electronic devices. ...
This article is about the software. ...
The introduction to this article provides insufficient context for those unfamiliar with the subject matter. ...
In a theoretical sense, the Church-Turing thesis implies that any operating environment can be emulated within any other. In practice, it can be quite difficult, particularly when the exact behavior of the system to be emulated is not documented and has to be deduced through reverse engineering. It also says nothing about timing constraints; if the emulator does not perform as quickly as the original hardware, the emulated software may run much more slowly than it would have on the original hardware. In computability theory the Church-Turing thesis, Churchs thesis, Churchs conjecture or Turings thesis, named after Alonzo Church and Alan Turing, is a hypothesis about the nature of mechanical calculation devices, such as electronic computers. ...
Reverse engineering (RE) is the process of taking something (a device, an electrical component, a software program, etc. ...
Structure
Most emulators just emulate a hardware architecture — if a specific operating system is required for the desired software, it must be provided as well (and may itself be emulated). Both the OS and the software will then be interpreted by the emulator, rather than being run by native hardware. Apart from this interpreter for the emulated machine's language, some other hardware (such as input or output devices) must be provided in virtual form as well: if writing to a specific memory location should influence the screen, for example, this will have to be emulated as well. An interpreter is a computer program that executes other programs. ...
A system of codes directly understandable by a computers CPU is termed this CPUs native or machine language. ...
Instead of full emulation of the hardware, a compatibility layer may suffice. This translates system calls for the emulated system into system calls for the host system. In software engineering, a compatibility layer allows binaries for an emulated system to run on a host system. ...
Developers of software for embedded systems or video game consoles often design their software on especially accurate emulator called a simulator before trying it on the real hardware. This is so that software can be produced and tested before the final hardware exists in large quantities, so that it can be tested without taking the time to copy the program to the hardware, or so that it can be debugged at a low level without introducing the side effects of a debugger. To meet Wikipedias quality standards, this article or section may require cleanup. ...
A video game console is a dedicated electronic machine designed to play video games. ...
A simulation is an imitation of some real device or state of affairs. ...
A debugger is a computer program that is used to debug (and sometimes test or optimize) other programs. ...
Typically, an emulator is divided into modules that correspond roughly to the emulated computer's subsystems. Most often, an emulator will be composed of the following modules: A module is a software entity that groups a set of (typically cohesive) subprograms and data structures. ...
- a CPU emulator or CPU simulator (the two terms are mostly interchangeable)
- a memory subsystem module
- various I/O devices emulators
Buses are often not emulated, either for reasons of performance or simplicity, and virtual peripherals communicate directly with the CPU or the memory subsystem.
A detailed description of the internals of a specific emulator can be found in the ElectrEm article. ElectrEm [1] is an emulator of the Acorn Electron coded in platform neutral C++ using the Simple DirectMedia Layer library. ...
Memory subsystem It is possible for the memory subsystem emulation to be reduced to simply an array of elements each sized like an emulated word; however, this model falls very quickly as soon as any location in the computer's logical memory does not match physical memory.
This clearly is the case whenever the emulated hardware allows for advanced memory management (in which case, the MMU logic can be embedded in the memory emulator, made a module of its own, or sometimes integrated into the CPU simulator). MMU, short for Memory Management Unit, is a class of computer hardware components responsible for handling memory accesses requested by the CPU. Among the functions of such devices are the translation of virtual addresses to physical addresses (i. ...
Even if the emulated computer does not feature an MMU, though, there are usually other factors that break the equivalence between logical and physical memory: many (if not most) architecture offer memory-mapped I/O; even those that do not almost invariably have a block of logical memory mapped to ROM, which means that the memory-array module must be discarded if the read-onlyness of ROM is to be emulated. For more generic meanings of input/output port, see port (computing). ...
Read-only memory (ROM) is a class of storage media used in computers and other electronic devices. ...
As a result, most emulators implement at least two procedures for writing to and reading from logical memory, and it is these procedures' duty to map every access to the correct location of the correct object.
On a base-limit addressing system where memory from address 0 to address ROMSIZE is read-only memory, while the rest is RAM, something along the line of the following procedures would be typical:
void WriteMemory(word Address, word Value) { word RealAddress; RealAddress=Address+BaseRegister; if(RealAddress<LimitRegister) { if(RealAddress>ROMSIZE) Memory[RealAddress]=Value; } else { RaiseInterrupt(INT_SEGFAULT); } } word ReadMemory(word Address) { word RealAddress; RealAddress=Address+BaseRegister; if(RealAddress<LimitRegister) { return Memory[RealAddress]; } else { RaiseInterrupt(INT_SEGFAULT); return NULL; } }
CPU simulator The CPU simulator is often the most complicated part of an emulator. Many emulators are written using "pre-packaged" CPU simulators, in order to concentrate on good and efficient emulation of a specific machine.
The simplest form of a CPU simulator is an interpreter, which follows the execution flow of the emulated program code and, for every machine code instruction encountered, executes operations on the host processor that are semantically equivalent to the original instructions. An interpreter is a computer program that executes other programs. ...
This is made possible by assigning a variable to each register and flag of the simulated CPU. The logic of the simulated CPU can then more or less be directly translated into software algorithms, creating a software re-implementation that basically mirrors the original hardware implementation. In computer science and mathematics, a variable (sometimes called a pronumeral) is a symbol denoting a quantity or symbolic representation. ...
In computer architecture, a processor register is a small amount of very fast computer memory used to speed the execution of computer programs by providing quick access to commonly used values—typically, the values being in the midst of a calculation at a given point in time. ...
In computer programming, flag refers to one or more bits that are used to store a binary value or code that has an assigned meaning. ...
The following example illustrates how CPU simulation is accomplished by an interpreter. In this case, interrupts are checked-for before every instruction executed, though this behavior is rare in real emulators for performance reasons.
void Execute(void) { if(Interrupt!=INT_NONE) { SuperUser=TRUE; WriteMemory(++StackPointer, ProgramCounter); ProgramCounter=InterruptPointer; } switch(ReadMemory(ProgramCounter++)) { // Handling of every valid instruction default: Interrupt=INT_ILLEGAL; } } Interpreters are very popular as CPU simulators, as they are much simpler to implement than more performant alternative solutions, and their speed is more than adequate for emulating computers of more than roughly a decade ago on modern machines. This is a list of decades which have articles with more information about them. ...
However, the speed penalty inherent in interpretation can be a problem when emulating computers whose processor speed is on the same order of magnitude as the host machine. Until not many years ago, emulation in such situations was considered completely impractical by many. An order of magnitude is the class of scale or magnitude of any amount, where each class contains values of a fixed ratio to the class preceding it. ...
What allowed breaking through this restriction were the advances in dynamic recompilation techniques. Simple a priori translation of emulated program code into code runnable on the host architecture is usually impossible because of several reasons: It has been suggested that Dynarec be merged into this article or section. ...
- code may be self-modifying
- there may not be a way to reliably distinguish data segments (which must not be translated) from text segments (code segments)
- there may not be a way to communicate with the emulated operating system in order for the emulator to be aware of newly loaded (for example from disk) code
Various forms of dynamic recompilation, including the popular Just In Time compiler (JIT) technique, try to circumvent these problems by waiting until the processor control flow jumps into a location containing untranslated code, and only then ("just in time") translates a block of the code into host code that can be executed. The translated code is kept in a code cache, and the original code is not lost or affected; this way, even data segments can be (meaninglessly) translated by the recompiler, resulting in no more than a waste of translation time. In computer science, self-modifying code is code that modifies itself on purpose. ...
Data is one of the sections of a program in an object file or in memory, which contains the global variables that are initialized by the programmer. ...
A text segment is the code (computer programming) in an object file. ...
See also Just in time for the business technique In computing, just-in-time compilation (JIT), also known as dynamic translation, is a technique for improving the performance of interpreted programs. ...
Look up cache in Wiktionary, the free dictionary. ...
I/O Most emulators do not, as mentioned earlier, emulate the main system bus; each I/O device is thus often treated as a special case, and no consistent interface for virtual peripherals is provided.
This can result in a performance advantage, since each I/O module can be tailored to the characteristics of the emulated device; designs based on a standard, unified I/O API can however rival such simpler models, if well thought-out, and they have the additional advantage of "automatically" providing a plug-in service through which third-party virtual devices can be used within the emulator. An application programming interface (API) is the interface that a computer system, library or application provides in order to allow requests for service to be made of it by other computer programs, and/or to allow data to be exchanged between them. ...
A unified I/O API may not necessarily mirror the structure of the real hardware bus: bus design is limited by several electric constraints and a need for hardware concurrency management that can mostly be ignored in a software implementation. Parallel programming is a computer programming technique that provides for the execution of operations in parallel, either within a single computer, or across a number of systems. ...
Even emulators that treat each device as a special case, there is usually a common basic infrastructure for
- managing interrupts, by means of a procedure that sets flags readable by the CPU simulator whenever an interrupt is raised, allowing the virtual CPU to "poll for (virtual) interrupts"
- writing to and reading from physical memory, by means of two procedures similar to the ones dealing with logical memory (although, contrary to the latter, the former can often be left out, and direct references to the memory array be employed instead)
In computer science, an interrupt is an asynchronous signal from hardware or software indicating the need for attention. ...
See also This article is in need of attention from an expert on the subject. ...
An arcade emulator is a program that emulates one or more arcade games on a different computer, such as a PC. See the List of emulators for examples of arcade emulators. ...
A console emulator is a program that allows a computer to emulate a video game console. ...
A field-programmable gate array or FPGA is a gate array that can be reprogrammed after it is manufactured, rather than having its programming fixed during the manufacturing — a programmable logic device. ...
In computing, binary translation is the emulation of one instruction set by another through translation of code. ...
A fan translation is an unofficial translation of a computer game or video game, sometimes into a language that it was never marketed in. ...
Game Engine Recreations are engine interpreters for video games that replace the original engine binary that came with the original game. ...
An in-circuit emulator (ICE) also called on-circuit debugger (OCD) or background debug module (BDM) is a hardware device used to debug the software of an embedded system. ...
In general terms, a virtual machine in computer science is software that creates an environment between the computer platform and the end user in which the end user can operate software. ...
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