A computer architecture simulator is a
program that simulates the
execution
Capital punishment, also known as the death penalty and formerly called judicial homicide, is the state-sanctioned killing of a person as punishment for actual or supposed misconduct. The sentence ordering that an offender be punished in ...
of
computer architecture.
Computer architecture simulators are used for the following purposes:
* Lowering cost by evaluating hardware designs without building physical hardware systems.
* Enabling access to unobtainable hardware.
* Increasing the precision and volume of computer performance data.
* Introducing abilities that are not normally possible on real hardware such as running code backwards when an error is detected or running in faster-than-
real time.
Categories
Computer architecture simulators can be classified into many different categories depending on the context.
* Scope:
Microarchitecture simulators model the
microprocessor
A microprocessor is a computer processor (computing), processor for which the data processing logic and control is included on a single integrated circuit (IC), or a small number of ICs. The microprocessor contains the arithmetic, logic, a ...
and its components. Full-system simulators also model the processor, memory systems, and I/O devices.
* Detail: Functional simulators, such as
instruction set simulators, achieve the same function as modeled components. They can be simulated faster if timing is not considered. Timing simulators are functional simulators that also reproduce timing. Timing simulators can be further categorized into digital cycle-accurate and analog sub-cycle simulators.
* Workload: Trace-driven simulators (also called event-driven simulators) react to pre-recorded streams of instructions with some fixed input. Execution-driven simulators allow dynamic change of instructions to be executed depending on different input data.
Full-system simulators
A full-system simulator is execution-driven architecture simulation at such a level of detail that complete software stacks from real systems can run on the simulator without any modification. A full system simulator provides virtual hardware that is independent of the nature of the host computer. The full-system model typically includes
processor core
A central processing unit (CPU), also called a central processor, main processor, or just processor, is the primary Processor (computing), processor in a given computer. Its electronic circuitry executes Instruction (computing), instructions ...
s,
peripheral devices,
memories, interconnection buses, and
network connections.
Emulators are full system simulators that imitate obsolete hardware instead of under development hardware.
The defining property of full-system simulation compared to an
instruction set simulator is that the model allows real
device drivers and
operating system
An operating system (OS) is system software that manages computer hardware and software resources, and provides common daemon (computing), services for computer programs.
Time-sharing operating systems scheduler (computing), schedule tasks for ...
s to be run, not just single programs. Thus, full-system simulation makes it possible to simulate individual computers and networked computer nodes with all their
software
Software consists of computer programs that instruct the Execution (computing), execution of a computer. Software also includes design documents and specifications.
The history of software is closely tied to the development of digital comput ...
, from network device drivers to operating systems,
network stacks,
middleware,
servers, and
application programs.
Full system simulation can speed the system development process by making it easier to detect, recreate and repair flaws. The use of
multi-core processors is driving the need for full system simulation, because it can be extremely difficult and time-consuming to recreate and debug errors without the controlled environment provided by virtual hardware. This also allows the software development to take place before the hardware is ready,
thus helping to validate design decisions.
Cycle-accurate simulator
A cycle-accurate simulator is a computer program that simulates a
microarchitecture on a cycle-by-cycle basis. In contrast an
instruction set simulator simulates an
instruction set architecture
In computer science, an instruction set architecture (ISA) is an abstract model that generally defines how software controls the CPU in a computer or a family of computers. A device or program that executes instructions described by that ISA, ...
usually faster but not cycle-accurate to a specific implementation of this architecture; they are often used when emulating older hardware, where time precision is important for legacy reasons. Often, a cycle-accurate simulator is used when designing new microprocessorsthey can be tested, and benchmarked accurately (including running full operating system, or compilers) without actually building a physical chip, and easily change design many times to meet expected plan.
Cycle-accurate simulators must ensure that all operations are executed in the proper virtual (or real if it is possible) timebranch prediction, cache misses, fetches, pipeline stalls, thread context switching, and many other subtle aspects of microprocessors.
See also
*
Instruction set simulator
References
External links
*The Archer virtual infrastructure for computer architecture simulation
*{{cite web, url=http://www.mikrocodesimulator.de/index_eng.php , title=Mikrocodesimulator MikroSim 2010 , publisher=0/1-SimWare , access-date=2010-12-06
Simulation software
Computer architecture