2.1 The Limits of Simulation

Simics is a system-level instruction set simulator. This means that:

• Simics models the target system at the level of individual instructions, executing them one at a time.
• Simics models the binary interface to hardware in sufficient detail that any software that runs on the real hardware will also run on Simics.

In practice, what this means is that there is no code that is too "low-level"—Simics can run, and debug, any kind of software: firmware, hardware drivers, operating systems, user-level applications, whatever. There are some caveats, though:

• Simics's model of time is rather simple; for example, it assumes by default that all instructions take the same amount of time to run. It is not difficult to write a program that uses this fact to detect the difference between Simics and real hardware. However, this is seldom a problem with real-world software.

  You can read more about Simics and time in the Understanding Simics Timing application note.

• The hardware models must be detailed enough. Models of nontrivial pieces of hardware do not typically model all functions and details of that hardware, so it is possible to write a program that detects the difference between Simics and real hardware by probing unimplemented functions. However, any given piece of software can be accommodated by extending the hardware models to cover the missing functions.

  You can read more about hardware modeling in the Simics Model Builder User's Guide.