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An emulator is '''Accuracyaccurate''' is how accurate when an instruction given to both the emulator is to program and the original hardwareresults in both outputting the same result. That means accurate emulators produce much less audio and video glitches at the cost of more processing power needed. Accuracy is most It's often achieved by using tighter syncingsynchronization. More  Notable accuracy means less graphics -centric emulators include [[Mesen]] (NES), [[higan]] (SNES), [[CEN64]] (N64) and audio glitches[[Exodus]] (Sega Mega Drive) among others.  The more accurate an emulator is, the lesser deviations there is from real hardware behavior but the more demanding it is. Ironically, that aspect might at times be at odds with how authentic the cost of additional CPU power required experience is, when it introduces [[Input lag]]. A similar debate surrounds CRT shaders as well. Not to run mention the game hardware intensive nature of very accurate emulators for later consoles may be at full odds with the emulator's usability, especially with the recent collapse of Moore's Law (in layman's terms, you can't just "buy a better PC" if semiconductor technology does not catch up fast enough with what it takes for accurate emulation that makes zero compromises for optimizing speed) As a result, accuracy and emulator authenticity continue to be controversial subjects and highly a matter of opinion depending on what aspect of the experience the user values more. ==Types:==

Low accuracy Newer emulators will have a large amount of visual and audio glitches. They will typically use various game-specific hacks tend to skip over problems, such as speed or compatibility issues with specific games. Many times, these emulator authors will only prioritize popular games, and the less popular games will be incompatible. An example of this is Speedy Gonzales: Los Gatos Bandidos with emulators such as [[ZSNES]] and [[Snes9x]], where the game will softfavor High-lock towards the end. This can also become very problematic when ROM hacks use these hacks to run by abusing the errors to create otherwise impossible behavior. This means that the ROM hack can only be used in that one specific emulator and is incompatible with real hardware (either through flash cart or reproduction). Such an issue has occurred with [[ZSNES]] and still occurs today with new N64 ROM hacks. Many times, newer emulators use High Level Emulation (HLE) as opposed to Low -Level Emulation (LLE), which results in lower accuracy. There are some exceptions to HLE causing low accuracy, such as the While emulators like [[Dolphin]] emulatorfavor accuracy but still retain HLE for performance and have successfully used it to an advantage, but these types of exceptions are uncommon. More information about this can be found at the and [[High/Low level emulation|it can still hinder accuracy]] page.

Medium accuracy Most emulators will headed by multiple developers tend to have fewer glitches, but will still , have many problems. Most emulators fall into this category.

High Emulator developers often strive for high accuracy emulators try to replicate when the system cannot effectively be cycle accurate. Their emulator replicates the components of the original system as closely as possible, and for as byuu explains it's that reason take that more CPU processing power is required to do so. They will have fewer The result is less audio and visual glitchesand better handling of edge cases used by creative game programmers. High An emulator with high accuracy emulators may or may not be cycle -accurate. Some high accuracy emulators can and sometimes, they achieve 100% compatibility with commercially released games.

Cycle accurate emulation is trying to perfectly emulate timings right down Emulating components according to their per-cycle accessesresults in cycle-accurate emulation. So each Each individual component is emulated and mutually synchronized at exactly the right time, in perfect sync, and so onsingle-clock resolution, which has a high higher CPU cost. The speed of the emulation depends on the way cycle -accuracy is implemented. Cycle accuracy , and it doesn't necessarily mean 100% accuracy. Only if the emulator is implemented perfectly is it perfect. An example of a cycle accurate emulator not being perfect is Even [[Higanhigan]] still has issues with the ROM Hack "Mario and Luigi: Kola Kingdom Quest," where it doesn't emulate the text glitch of the level's title. ===Subcycle accuracy===The heartbeat of an IC is its clock signal; a full cycle of the clock signal involves two transitions: from low to high and then back from high to low. Therefore even a chip that is fully synchronized to its clock may not be emulated accurately if it is emulated with only cycle precision as it'll have to bundle together both its rising and falling actions. The [[wikipedia:Zilog_Z80|Z80]] processor offers an example of this: almost all inputs are sampled on a rising clock but the WAIT signal is sampled on real hardwarea falling clock. E.g. in a standard three-clock-cycle memory access machine cycle the WAIT line is sampled on the final falling clock — 0.5 cycles before the end of the machine cycle. If the Z80 is required to wait, it will sample the WAIT line again at cycle intervals until it spots that it is no longer asserted and complete 0.5 cycles after that. Therefore an emulator that only cycles accurately will have to sample it either 0.5 cycles early or 0.5 cycles late, and will stop waiting either 0.5 cycles early or 0.5 cycles late, causing a phase error with whatever it was sampling. Worse than that, as the level title text has graphical glitches whereas those glitches do Z80 tests WAIT only once every machine cycle, not exist every clock cycle, missing it as a result of sampling at the wrong time can cause a net error of four or more cycles. Using the broad brush of cycle accuracy can also cause problems in machines with multiple clock signals — component A being accurate only to the complete clock cycle can leave it as observably inaccurate if component B is running with a quicker clock. A simple example of this can be found in the BBC Micro, where the 6522 timer chips run at 1Mhz while the CPU runs at 2Mhz. 6522s generate an interrupt half a cycle after they underflow. Therefore if the 6522s in a BBC Micro are emulated only in whole-cycle steps, they will observably trigger interrupts a cycle late from the point of view of the CPU. In practice, this can cause some copy protection mechanisms to fail. Impinging upon chip accuracy, some chips, such as the Commodore 64's [[Higanwikipedia:MOS_Technology_SID|SID]]are part digital and part analog. The analog part can be emulated in a discrete fashion, but it is often desirable to take those discrete steps at a multiple of the clock rate. However the difference is usually not observable to other components in the emulated machine so although this is subcycle accuracy as some part of the state of the chip is known as a precision of greater than one cycle, it doesn't tend to affect the design of the emulator as a whole.

Chip accurate emulation works by By simulating each logic chip on the board individually. Not , this not only does this take takes a tremendous amount of processing power or specialized hardware to run (as in, even emulating something from the 1970s on a chip accurate level would need DolphinAAA-level system requirements to run at a good speed.), but they it also require a requires an incredible amount of effort to make. This accuracy method is , and <u>it's also almost useless</u>. Although it is the only way to achieve ''true 100% '' hardware simulation, cycle accurate emulation can already achieve accuracy which is virtually indistinguishable accuracy from the real hardware, aside from a very limited amount negligible set of edge cases. In addition, cycle-accurate emulators have much lower system requirements and programming difficulty. Currently, the The only chip accurate emulators that are currently usable run on Field Programmable Gate Arrays, or FPGAs[[FPGA]]s, which are essentially custom programmable chips. Machines dedicated to this type of emulation exist, such as the WIP Zimba 3000 Analogue NT Mini by kevtrisor the RetroUSB AVS by bunnyboy. Other examples of chip accurate emulation can be found in flash carts such as the SD2SNES, where various add-on chips are emulated on the included FPGA.

This emulator needs type is unique in that its own section on accuracymethod, because its accuracy method is unique. [http://sourceforge.net/projects/dice/ [DICE] ], emulates arcade machines from the early 1970s. The architecture of these systems is different from a modern architecture, mostly because they don't have a CPU. DICE emulates the discrete logic components of the machines at a circuit level. Although and, although the results are accurate the , you need a fast 64-bit PC to run these arcade games at full speed. ==Perfection?==While it may be theoretically possible to have a 100% perfect emulator, that feat is very rare (if not nearly impossible), even for some highly regarded emulators such as [[higan]] or kevtris's work on the various FPGA-based consoles by Analogue. Just because an emulator claims to be "cycle accurate" or "100% compatible" does not mean that said emulator is flawless. This even includes situations in which all emulator accuracy tests (ie. [[PS1 Tests]]) are passed, as these tests cannot cover every single edge case, and some of these tests may even fail on real hardware, leading to even more confusion. Some things are nearly impossible to perfectly emulate, such as some of the illegal opcodes of the [[wikipedia:MOS_Technology_6502|6502]], where the results are completely unpredictable on hardware, and different hardware revisions have different results and different illegal opcodes. The closest one could get to writing a perfect emulator would be if someone were to exactly copy an original ASIC map or a decap onto an FPGA, and even then, that isn't always a magic bullet. While any given emulator may not be perfect, that does not mean that the emulator is bad by any means. Writing an accurate emulator is extremely hard work, and while perfection may be nearly impossible at the moment, that doesn't mean that games can't be enjoyed. Work on archival via emulation has come a very long way since the emulators of the 1990s, and things are only getting better from here, with excellent emulators such as the previously mentioned [[higan]] and kevtris's [[FPGA]] cores being available to use right now.

There are The accuracy debate has very clearly split into two sides when it comes to the issue of accuracy. One side argues that as long as an emulator plays the majority of games at full speed on most computers and devices without too many obvious glitches, it does not matter how accurately it actually replicates the original hardware and its many quirks and functions. The faithfulness of the emulator to the console it is emulating comes second to its overall ability to play games. The other side argues that an emulator should ultimately strive to simulate the hardware as much as possible, as that is the only way to achieve as much compatibility as possible, as well as the only way to preserve the hardware. Thus, speed and scalability to most devices is a lower priority to accuracy to the real console, both for purposes of compatibility and preservation.

Even within The ones that don't favor accuracy argue that emulators do not need to be as accurate as possible if it can play all the games they need. And because these games tend to be the second side, howevermost recognized alongside the console, there shouldn't really be an interest in making more games work since those ones do. A more compelling point is some disagreement that as to just long as an emulator plays the majority of games at full speed on most computers and devices without too many obvious glitches, it doesn't matter how much accuracy is actually neededaccurately it replicates the original hardware and its many quirks and functions. On most platforms, after obtaining a certain amount The faithfulness of accuracy, going further requires an exponential growth in system requirements, the results of which may not be noticeable emulator to the vast majority of users. Cycle accuracy in particular has been hotly debated in regards console it's emulating comes second to its usefulness, due overall ability to how such an extreme level of accuracy requires a lot of extra processing power for relatively few gains in compatibilityplay games.

The ones that favor accuracy explain their view in that when playing a game with inaccurate emulation the experience may sometimes be quite different to the real thing, particularly with games focused on split-second reactions. There is also an entirely different reason: archival. Emulator projects should ultimately strive to recreate the hardware as much as possible; that's the only way for it to be compatible, and that's the only way to preserve the hardware. Speed and scalability to most devices is a lower priority to accuracy to the real console, both for purposes of compatibility and preservation. Even within the second side, however, there is some disagreement as to just how much accuracy is actually needed. On most platforms, after obtaining a certain amount of accuracy, going further requires an exponential growth in system requirements, the results of which may not be noticeable to the vast majority of users. Cycle accuracy, in particular, has been hotly debated in regards to its usefulness, due to how such an extreme level of accuracy requires a lot of extra processing power for relatively few gains in compatibility. Simply put, it's a disagreement between wanting 'good enough' or perfection no matter , 'good for all cases', and 'good for the costfuture'.

Many consoles have different internal hardware revisions which degrade accuracy or change the consoles' behavior in another way, such as the SNES 1CHIP (various games have minor issues, such as a small mess of pixels at the top of the screen in games such as Super Ghouls 'n Ghosts or Demon's Crest), Genesis Model 3 (fixed a bug that some games such as Gargoyles used), various [[Commodore 64 emulators|Commodore 64]] revisions (fixed a useful bug that allowed for smooth horizontal scrolling), or PS2 SCPH-750XX (less compatibility with some PS2 games and PS1 games). These specific consoles are not generally emulated in their respective emulators, and those emulator developers tend to focus only on one revision. An exception to this is [[VICE]], which tries to emulate as many different revisions of the Commodore 64 as possible and as accurately as possible.

*[http://arstechnica.com/gaming/2011/08/accuracy-takes-power-one-mans-3ghz-quest-to-build-a-perfect-snes-emulator/Accuracy takes power: one man’s 3GHz quest to build a perfect SNES emulator] - Byuu ([[higan]] developer), 2011 *[httphttps://tasvideoswww.youtube.orgcom/EmulatorResources/NESAccuracyTests.html NES Accuracy Testswatch?v=oQZMVo_Fmrs Pokémon glitches and emulation accuracy]- TheZZAZZGlitch

===Accuracy Tests===*[[PS1 Tests]]*[[http:GB//tasvideos.org/EmulatorResources/GBAccuracyTests.html Game Boy Accuracy C Tests]]

===TASVideos===*[http://tasvideos.org/EmulatorResources/NESAccuracyTests.html NES Accuracy Tests]*[http://tasvideos.org/EmulatorResources/GBAccuracyTests.html Game Boy Accuracy Tests]*[http://tasvideos.org/EmulatorResources/SNESAccuracyTests.html SNES Accuracy Tests]