sdf-parser

A pure-Python parser for Standard Delay Format (SDF) files — the industry-standard format used by EDA tools to back-annotate timing delays and constraints onto digital designs.

Building a Python SDF Parser for EDA Flow Automation — Closing a tooling gap that every EDA engineer eventually runs into.

Features

• Parses IOPATH, COND, CONDELSE, WIDTH, SETUPHOLD, and RECREM
• Single file or directory of SDF files (with cross-file consistency checks)
• Single-cell extraction mode — stops early once the target cell is found
• Zero required dependencies — only the Python standard library
• Optional colored warnings via termcolor
• CLI included: sdf-parser timing.sdf --cell INV_X1

Installation

pip install eda-sdf-parser                  # no extra dependencies
pip install "eda-sdf-parser[color]"         # adds termcolor for colored warnings

Or for development:

git clone https://github.com/rohaansch/sdf-parser
cd sdf-parser
pip install -e ".[dev]"

Quick start

from sdf_parser import SDFParser

parser = SDFParser()
sdf = parser.read("timing.sdf")

print(repr(sdf))
# SDF(cells=142, files=1, header=['SDFVERSION', 'DESIGN', 'TIMESCALE'])

for entry in sdf.cells["INV_X1"]:
    print(entry)
# ['IOPATH', 'A', 'ZN', 2]
# ['COND', "A==1'b0", 'A', 'ZN', 1]
# ['WIDTH', None, 'posedge', 'A', 1]

Parsed entry format

Each entry in sdf.cells["CELLNAME"] is a list whose first element is the construct keyword:

Construct	Entry format
IOPATH	[IOPATH, pin_1, pin_2, n]
COND	[COND, condition, pin_1, pin_2, n]
CONDELSE	[CONDELSE, pin_1, pin_2, n]
WIDTH	[WIDTH, condition, edge, port, n]
SETUPHOLD	[SETUPHOLD, cond_1, edge_1, port_1, cond_2, edge_2, port_2, n]
RECREM	[RECREM, cond_1, edge_1, port_1, cond_2, edge_2, port_2, n]

condition is None when no COND qualifier is present. n is the number of delay value tuples (e.g. 3 for min/typ/max).

Full example

SDF input:

(CELL
  (CELLTYPE "DFFS_X2")
  (INSTANCE FF1)
  (TIMINGCHECK
    (SETUPHOLD (posedge D) (posedge CK) (0.1:0.1:0.1) (0.05:0.05:0.05))
    (RECREM   (negedge SN) (posedge CK) (0.2:0.2:0.2) (0.1:0.1:0.1))
    (WIDTH    (posedge CK) (0.3:0.3:0.3))
  )
)

Python output:

sdf.cells["DFFS_X2"]
# [
#   ['SETUPHOLD', None, 'posedge', 'D', None, 'posedge', 'CK', 2],
#   ['RECREM',    None, 'negedge', 'SN', None, 'posedge', 'CK', 2],
#   ['WIDTH',     None, 'posedge', 'CK', 1],
# ]

API reference

SDFParser(path=None)

Create a parser. path sets the default file/directory used by read().

SDFParser.read(path=None, given_cell=None) → SDF

Argument	Type	Description
path	str	.sdf file or directory. Falls back to the constructor path.
given_cell	str	Extract only this cell (case-insensitive).

Raises ValueError / FileNotFoundError / IOError on bad input.

SDFParser.reset()

Clear internal state to reuse the parser for a different file:

sdf_fast = parser.read("fast.sdf")
parser.reset()
sdf_slow = parser.read("slow.sdf")

SDF object

Attribute	Type	Description
header_data	dict	Header fields (SDFVERSION, DESIGN, TIMESCALE, …)
cells	dict[str, list]	Cell name → list of parsed entries
files	list[str]	All files that contributed to this object

format_entries(cell) → str

Format a cell's entries as a human-readable multi-line string:

from sdf_parser import format_entries
print(format_entries(sdf.cells["INV_X1"]))

Parsing a directory

When path is a directory every .sdf file inside it is parsed and merged. Cells found in multiple files are compared; mismatches produce a warning:

sdf = SDFParser().read("sdf_corners/")
print(repr(sdf))
# SDF(cells=142, files=3, header=['SDFVERSION', 'DESIGN', 'TIMESCALE'])

Command-line usage

sdf-parser timing.sdf
sdf-parser timing.sdf --cell INV_X1
sdf-parser timing.sdf --cell INV_X1 --header
sdf-parser sdf_corners/ --header
sdf-parser --version

Or without installing:

python -m sdf_parser timing.sdf --cell INV_X1

Limitations

• Delay values are not parsed — only the count of value tuples is stored.
• Only the constructs listed above are extracted; other SDF keywords are skipped.
• OASIS and binary SDF formats are not supported.

Running the tests

pip install -e ".[dev]"
pytest -v

License

MIT