OpenRAM

An open-source static random access memory (SRAM) compiler.

What is OpenRAM?

OpenRAM is an open-source Python framework to create the layout, netlists, timing and power models, placement and routing models, and other views necessary to use SRAMs in ASIC design. OpenRAM supports integration in both commercial and open-source flows with both predictive and fabricable technologies.

Basic Setup

The OpenRAM compiler has very few dependencies:

• Ngspice 26 (or later) or HSpice I-2013.12-1 (or later) or CustomSim 2017 (or later)
• Python 3.5 and higher
• Python numpy (pip3 install numpy to install)
• flask_table (pip3 install flask to install)

If you want to perform DRC and LVS, you will need either:

• Calibre (for FreePDK45 or SCMOS)
• Magic + Netgen (for SCMOS only)

You must set two environment variables: OPENRAM_HOME should point to the compiler source directory. OPENERAM_TECH should point to a root technology directory that contains subdirs of all other technologies. For example, in bash, add to your .bashrc:

  export OPENRAM_HOME="$HOME/openram/compiler"
  export OPENRAM_TECH="$HOME/openram/technology"

For example, in csh/tcsh, add to your .cshrc/.tcshrc:

  setenv OPENRAM_HOME "$HOME/openram/compiler"
  setenv OPENRAM_TECH "$HOME/openram/technology"

We include the tech files necessary for FreePDK45 and SCMOS. The SCMOS spice models, however, are generic and should be replaced with foundry models. If you are using FreePDK45, you should also have that set up and have the environment variable point to the PDK. For example, in bash, add to your .bashrc:

  export FREEPDK45="/bsoe/software/design-kits/FreePDK45"

For example, in csh/tcsh, add to your .tcshrc:

  setenv FREEPDK45 "/bsoe/software/design-kits/FreePDK45"

We do not distribute the PDK, but you may download FreePDK45

If you are using SCMOS, you should install Magic and Netgen. We have included the SCN4M design rules from Qflow.

Basic Usage

Once you have defined the environment, you can run OpenRAM from the command line using a single configuration file written in Python. For example, create a file called myconfig.py specifying the following parameters:

word_size = 2
num_words = 16

tech_name = "scn4m_subm"
process_corners = ["TT"]
supply_voltages = [ 3.3 ]
temperatures = [ 25 ]

output_path = "temp"
output_name = "sram_{0}_{1}_{2}".format(word_size,num_words,tech_name)

drc_name = "magic"
lvs_name = "netgen"
pex_name = "magic"

and run OpenRAM by executing:

$OPENRAM\_HOME/openram.py myconfig

You can see all of the options for the configuration file in $OPENRAM_HOME/options.py

Directory Structure

• compiler - openram compiler itself (pointed to by OPENRAM_HOME)
  • compiler/base - base data structure modules
  • compiler/pgates - parameterized cells (e.g. logic gates)
  • compiler/bitcells - various bitcell styles
  • compiler/modules - high-level modules (e.g. decoders, etc.)
  • compiler/verify - DRC and LVS verification wrappers
  • compiler/characterizer - timing characterization code
  • compiler/gdsMill - GDSII reader/writer
  • compiler/router - router for signals and power supplies
  • compiler/tests - unit tests
• technology - openram technology directory (pointed to by OPENRAM_TECH)
  • technology/freepdk45 - example configuration library for [FreePDK45 technology node
  • technology/scn4m_subm - example configuration library SCMOS technology node
  • technology/scn3me_subm - unsupported configuration (not enough metal layers)
  • technology/setup_scripts - setup scripts to customize your PDKs and OpenRAM technologies
• docs - LaTeX manual (outdated)
• lib - IP library of pregenerated memories

Unit Tests

Regression testing performs a number of tests for all modules in OpenRAM. From the unit test directory ($OPENRAM_HOME/tests), use the following command to run all regression tests:

   python3 regress.py

To run a specific test:

   python3 {unit test}.py 

The unit tests take the same arguments as openram.py itself.

To increase the verbosity of the test, add one (or more) -v options:

   python3 tests/00_code_format_check_test.py -v -t freepdk45

To specify a particular technology use "-t " such as "-t freepdk45" or "-t scn4m_subm". The default for a unit test is scn4m_subm. The default for openram.py is specified in the configuration file.

Creating Custom Technologies

If you want to support a enw technology, you will need to create:

• a setup script for each technology you want to use
• a technology directory for each technology with the base cells

All setup scripts should be in the setup_scripts directory under the $OPENRAM_TECH directory. We provide two technology examples for SCMOS and FreePDK45. Please look at the following file for an example of what is needed for OpenRAM:

  $OPENRAM_TECH/setup_scripts/setup_openram_freepdk45.py

Each setup script should be named as: setup_openram_{tech name}.py.

Each specific technology (e.g., FreePDK45) should be a subdirectory (e.g., $OPENRAM_TECH/freepdk45) and include certain folders and files:

• gds_lib folder with all the .gds (premade) library cells:
  • dff.gds
  • sense_amp.gds
  • write_driver.gds
  • cell_6t.gds
  • replica_cell_6t.gds
• sp_lib folder with all the .sp (premade) library netlists for the above cells.
• layers.map
• A valid tech Python module (tech directory with init.py and tech.py) with:
  • References in tech.py to spice models
  • DRC/LVS rules needed for dynamic cells and routing
  • Layer information
  • Spice and supply information
  • etc.

Get Involved

• Report bugs by submitting Github issues.
• Develop new features (see how to contribute)
• Submit code/fixes using a Github pull request
• Follow our project.
• Read and cite our ICCAD paper

License

OpenRAM is licensed under the BSD 3-clause License.

Contributors & Acknowledgment

• Matthew Guthaus from VLSIDA created the OpenRAM project and is the lead architect.
• James Stine from VLSIARCH co-founded the project.
• Hunter Nichols maintains and updates the timing characterization.
• Michael Grims created and maintains the multiport netlist code.
• Jennifer Sowash is creating the OpenRAM IP library.
• Jesse Cirimelli-Low created the datasheet generation.
• Samira Ataei created early multi-bank layouts.
• Bin Wu created early parameterized cells.
• Yusu Wang is porting parameterized cells to new technologies.
• Brian Chen created early prototypes of the timing characterizer.
• Jeff Butera created early prototypes of the bank layout.

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