Simics Resources
Simics tech site | GEMS | Simics user guides

Simics is a full-system functional extensible hardware simulator. The information on this web site assumes running simics 3.0.x or greater.

  • Full-system means that you can run the entire system software package, i.e., the operating system, the application software, on hardware platforms supported by simics.
  • Functional means that you can execute most of the software that runs on the target architecture, and it will function correctly, i.e., it will compute PI, produce correct output, read and write files, etc. However, a plain-vanilla simics will not simulate microarchitectural details of the processor. So your instructions will run with no delays or optimizations, allowing each instruction to complete within one processor cycle. If you want to do interesting simulations with Simics, you need to use simics extensions.
  • Extensible means that you can extend simics to simulate microarchitectural details of your target processor. For example, you can add a multi-level cache hierarchy, a set of interconnects, etc. You can even implement your own hardware counters. Simics comes with its own set of modules allowing to simulate cache hierarchies (including CMP caches), SMT, and a simple Niagara machine. A popular set of extension modules GEMS was developed at University of Wisconsin. GEMS allows simulation of chip multiprocessor architectures and other cool things.
Getting started:
  1. Initialize your Simics workspace
  2. Creating your own modules
  3. Getting help with Simics
  4. Apply for a personal academic license

Advanced Simics Topics:

  1. How to configure a CMP cache architecture
  2. How to simulate an SMT CPU
  3. Using existing Simics configurations
  4. Copying files to a simulated machine (SimicsFS)
  5. Making your simulations fast

Initialize your Simics workspace

  1. Pick a host machine (or several) where you will run your Simics simulations. Click here for a list of CPU servers where you can run simics.
  2. Register as a Simics forum user on the simics tech site.
  3. Create and configure your own workspace
    (Use the same steps to update an existing workspace)
    • Create a directory for your simics workspace, such as ~/my-simics-workpace.
    • If you will run Simics on a Linux/x86 host:(oak, cs-app1, cs-app2)
      • From ~/my-simics-workspace run "/cs/systems/Simics/Linux-x86/simics-3.0.26/bin/workspace-setup"
      • From ~/my-simics-workspace run "/cs/systems/Simics/Linux-x86/simics-3.0.26/configure --with-host=x86-linux"
    • If you will run Simics on a Solaris/SPARC host(dinosaur, coolthreads)
      • From ~/my-simics-workspace run "/cs/systems/Simics/Solaris-SPARC/simics-3.0.26/bin/workspace-setup"
      • From ~/my-simics-workspace run "/cs/systems/Simics/Solaris-SPARC/simics-3.0.26/configure --with-host=v9-sol8-64"
  4. Run simics, make sure everything works
    • From ~/my-simics-workspace run "./simics targets/ebony/ebony-linux-firststeps.simics".
      Note: This will pop up an xterm window, so make sure your DISPLAY variable is set appropriately.
      For example, if you log in from to, and you run Simics on oak, on oak execute command "setenv DISPLAY" if you use cshell, or "; export DISPLAY" if you are using bash.

Create your own modules

To make changes to Simics, you'd need to create your own modules, similar to GEMS modules. Simics is a modular simulator, and it comes with a set of default modules. To find out how they are implemented, so you can model your modules after, them, check out /cs/systems/Simics/Solaris-SPARC/simics-3.0.26/src/extensions. For example, a g-cache directory contains a code for a cache module, sample-memhier - (you guessed) a sample memory hierarchy. So if you'd like to modify existing simics modules you can copy the source code into your work space and hack away! To find out how to add a new module and compile it, refer to the simics programming guide.

Getting Help with Simics

The main sources of help with Simics are:

  • Simics user guides. These include general guides, platform-specific guides, a programming guide, etc.
  • Simics forum. This is a very important source. Simics documentation is very spartan, so in many cases you will not be able to find what you need in the user guides. In that case, post your question to the simics forum. You will get an almost instantaneous response! Just remember, the better you formulate your question, the better answer you will get.

Applying for a Personal Academic License

  • Apply using a link at the simics tech site.
  • You will be asked to provide the lmhostid of the machine where you will run Simics.
    Find out the lmhostid by executing the FLEXLM lmutil software on the host machine where you will run Simics.
    • If you run on a Linux/x86 host:
      Run "/cs/systems/Simics/Linux-x86/simics-3.0.26/x86-linux/sys/flexlm/bin/lmutil lhmostid "
    • If you run on a Solaris/SPARC host
      Run "/cs/systems/Simics/Solaris-SPARC/simics-3.0.26/v9-sol8-64/sys/flexlm/bin/lmutil lhmostid"
    • For other hardware platforms, download lmutil here.
  • If you want to run simics simulations on multiple hosts you need to apply for multiple licenses. This is perfectly legal.
  • Install your personal license.
    • Create a directory <my-simics-workspace>/licenses
    • Copy the license file you received from Virtutech to that directory
    • Create a file ~/.flexlmrc
    • In that file insert the following line: LM_LICENSE_FILE=<my-simics-workspace>/licenses . You need to specify a full directory name, do not use "~/" to point to your home directory.

How to Configure a CMP Cache Architecture

Refer to the section Simics User Guide >> Advanced Simics Usage >> Cache Simulation >> A More Complex Cache System in the Simics User guide. Another example can be found in this posting on the Simics forum. You can also use several pre-made scripts for a peanut target (will work with existing peanut configurations).

(Note: the above scripts depend on another common script located at /cs/systems/Simics/Scripts/Caches/common.simics)

To configure your simulated system to use on of these caches, run simics like this:
./simics -stall -c <configuration> <cache-script>

"stall" option is important for correct simulation of timing due to cache access.

Alternatively, you can add the cache after you have started your target system by typing at the simics command prompt:
simics> run-command-file <cache-script>

How to Simulate an SMT CPU

Try searching/posting in the simics forum. A good way to start is by looking at this post.

Using Existing Simics Configurations

Simics simulates the actions of hardware in software, so executing a program on Simics takes much longer than on real hardware. To save time, you can use existing Simics configurations, i.e., saved simulator state from which you can continue the simulation. For example, you may boot the operating system and save the resulting configuration, then you can use that configuration as a starting points for running benchmarks on Simics. This way you won't have to boot the operating system every time you run a new benchmark.

There are several simics configurations that have been prepared for you by the course instructor. To run simics with an existing configuration, use the following command:

./simics -c <path to configuration files>

Here is a list of available configuration files for Niagara - all with SimicsFS installed:

  • Niagara 1 core, 1 thread/core:
  • Niagara 1 core, 2 threads/core:
  • Niagara 8cores, 4 threads/core:

For simulations of CMP and multi-CMP machines, you can use peanut configurations:

  • Peanut 1 core:
    With SimicsFS:
  • Peanut 2 cores:
    With SimicsFS:
  • Peanut 4 cores:
    With SimicsFS:

Copying files to a simulated machine

You will need to use SimicsFS (see Simics user guide, section 7.3). Some configurations already have SimicsFS installed. All Niagara configurations come with SimicsFS. Configurations for other platforms with SimicsFS installed will have "simicsFS" in their name. If you need to install SimicsFS, you can use a script for Solaris 10 simulated machine:

Making your simulations fast.

Simics simulates actions of the hardware entirely in software. Therefore, your benchmarks will run much more slowly that on real hardware. Depending on your set-up it may take more than one hour to simulate one second of real time. Therefore, you want to do your best to ensure that your simulations run efficiently.

Simics is a CPU-intensive application. Your simulations will run quickly if your simics application uses a dedicated CPU. When you log onto a CPU server, check that there are CPUs available by running top. That command will show you the list of running jobs and their CPU utilizations. If you see that there are as many CPU-intensive jobs as there are CPUs on that system, you are better off running your simulation on another machine.

Another consideration is memory. If there isn't enough physical memory for a simics run on your machine, the memory will be swapped to disk. This will significantly slow down your simulation. (A sign that your simulation is swapping is if your simics instance has CPU utilization well below 100% check that by running top.) If that's the case, you are better off limiting the amount of memory that simics is allowed to use. To do this, run simics like this: simics -e 'set-memory-limit 500.