SRAM 22

A Configurable SRAM Generator

SRAM22 parametrically generates SRAM blocks. At the moment, we only support the SKY130 process. SRAM22 is still a work in progress.

Dependencies

In order to use SRAM22, your system will need to have the following components:

• Rust (SRAM22 is tested with version 1.81.0)
• Make
• A local clone of our slightly modified version of the SKY 130 PDK. You will also need to set the environment variable SKY130_OPEN_PDK_ROOT to the absolute path of the local PDK's root directory. Substrate uses standard cells from the sky130_fd_sc_hs library, so you will also need to run the following from the PDK root directory:

  git submodule update --init libraries/sky130_fd_sc_hs/latest
  

Installation

BWRC

If you have BWRC access, you can install all features of SRAM22. Make sure that you have SSH access to bwrcrepo.eecs.berkeley.edu from a BWRC machine by adding your SSH key to your GitLab account. You will then need to add the following lines to your ~/.cargo/config.toml file:

[net]
git-fetch-with-cli = true
[registries]
substrate = { index = "https://github.com/substrate-labs/crates-index" }

You can then install SRAM22 using the following commands:

git clone https://github.com/rahulk29/sram22.git
cd sram22 && mv Cargo.bwrc.toml Cargo.toml && make install && cd -

External

If you do not have BWRC access, you can still install SRAM22, albeit without the ability to invoke proprietary tools for DRC, LVS, PEX, and simulation.

Use the following commands:

git clone https://github.com/rahulk29/sram22.git
cd sram22 && make install && cd -

Usage

sram22 0.2.0
Rahul Kumar <rahulkumar@berkeley.edu>, Rohan Kumar <rohankumar@berkeley.edu>
A configurable SRAM generator

Usage: sram22 [OPTIONS]

Options:
  -c, --config <CONFIG>          Path to TOML configuration file [default: sram22.toml]
  -o, --output-dir <OUTPUT_DIR>  Directory to which output files should be saved
      --lef                      Generate LEF (used in place and route)
      --liberate                 Generate LIB with Liberate MX instead of the interpolation model
      --drc                      Run DRC using Calibre
      --lvs                      Run LVS using Calibre
  -a, --all                      Run all available steps
  -p, --parallel <PARALLEL>      Max number of SRAMs to generate concurrently [default: no limit]
  -h, --help                     Print help information
  -V, --version                  Print version information

--liberate, --drc, --lvs, and --all are only available with a full (commercial) installation.

By default all SRAMs are generated concurrently. Pass --parallel (or -p) to cap how many run at once — useful in a commercial install, where each SRAM also runs PEX and Liberate MX steps that invoke licensed tools and are memory-intensive.

Configuration

SRAM22 generates memory blocks based on a TOML configuration file. Configurations are specified as an array of [[sram]] configurations, allowing up to multiple SRAMs to be generated.

[[sram]]
num_words = 64
data_width = 32
mux_ratio = 4
write_size = 8

[[sram]]
num_words = 256
data_width = 64
mux_ratio = 4
write_size = 8
# The `pex_level` flag is only available with a full installation.
pex_level = "rcc"

Save this as sram22.toml and run:

sram22

Each [[sram]] block is generated independently. Output files are placed in subdirectories named after the SRAM (e.g. build/sram22_64x32m4w8/)

The number of rows in the SRAM bitcell array is num_words / mux_ratio. The number of columns in the array is data_width * mux_ratio.

A valid configuration must have:

• A mux_ratio of 4 or 8
• A data_width that is an integer multiple of the write_size
• A power-of-two number of rows
• At least 16 rows
• At least 16 columns
• pex_level (optional): Must be "r", "c", "rc", or "rcc". Only available with a full installation. When set, PEX runs automatically — no additional flag required. Each [[sram]] block sets its own pex_level independently; SRAMs without it skip PEX. The extracted netlist is only consumed by Liberate MX (see below).

LIB generation

SRAM22 always generates Liberty (.lib) timing files for the tt/ss/ff PVT corners — no flag is required. By default the LIB is produced by an open-source interpolation model; interpolated LIBs carry a conservative overestimate of up to 2% for SRAM configurations with data_width between 8 and 128. data_width outside that range is not supported by the open-source model and will produce an error.

With a full BWRC installation, passing --liberate instead characterizes the LIB with Liberate MX running SPICE simulation; interpolation is skipped in that case. --all does not select Liberate MX — it still generates the LIB by interpolation. If a config also has pex_level set, Liberate MX uses the extracted netlist; otherwise it falls back to the plain SPICE netlist.

Contribution

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you shall be licensed under the BSD 3-Clause license, without any additional terms or conditions.