Simulation

Simulation is used to support the behavioral design process by taking the the current representation of the system design and exercising that system using a test bench that generates the necessary external stimuli needed to make the design under test function. It supports activities including, analysis of system behaviour including timing, execution of the system model functions and in some cases develop and debug software that will operate in the system. 

The system design, in the form of an behavioural model, expressed in abstract form called register-transfer level (RTL) is compiled along with timing files ( .lib) that include the behavioural description including necessary delay information about standard cells. These files are provided by industry or open source resources. The compiled model is then executed in a simulation environment and the outputs such as a waveform database can be viewed to investigate the operation of the design under test. Simulation tools usually have visual interfaces for things like waveform display, design analysis, simulator command and debug. 

There are many alternate simulation environments. 

Some examples of Simulation environments

Arm provides Fast Models that are 100% functionally accurate and provide programmer's view models of Arm IP to aid software development. Fast Models trade off higher simulation speed for a higher level of abstraction compared to complete Cycle Models. 

Arm Cycle Models are 100% cycle accurate models compiled from RTL and can be used in SystemC simulation environments or RTL simulators. Engineers can examine signals, dump waveforms, and trace execution through the system. A register accurate and fully functional model can be used to develop and debug software. Engineers are able to view software source code, control the simulation at clock edge granularity, and examine registers and memories.