CMOS standard-cell characterization kit.
Project description
LibreCell - Lib
Characterization kit for CMOS cells. This Python package comes with a some stand-alone command-line tools:
- Most notably
lctime
for recognition and characterization of combinational and sequential cells. sp2bool
: Recognition ('reverse engineering') of transistor networks. This is intended for analyzis and debugging.libertyviz
: Visualization of NDLM tables.
Getting started
# Clone this repository.
git clone https://codeberg.org/librecell/lctime
cd lctime
# Install
./install_develop.sh
# Run tests
cd tests
./run_tests.sh
Characterize a cell
An ready-to-run example can be found in the examples
folder.
The script run_example.sh
should characterize the INVX1
inverter.
The following example determines the input capacitances and timing delays of a combinational cell.
It is assumed that FreePDK45
is installed in the users home directory.
Required inputs are:
- --liberty: A template liberty file which defines how the cells should be characterized.
- --include: SPICE files or models to be included.
- --spice: A SPICE file which contains the transistor level circuit of the cell (best including extracted parasitic capacitances).
- --cell: Name of the cell to be characterized.
- --output: Output liberty file which will contain the characterization data.
Characterize a single cell:
lctime --liberty ~/FreePDK45/osu_soc/lib/files/gscl45nm.lib \
--include ~/FreePDK45/osu_soc/lib/files/gpdk45nm.m \
--output-loads "0.05, 0.1, 0.2, 0.4, 0.8, 1.6" \
--slew-times "0.1, 0.2, 0.4, 0.8, 1.6, 3.2" \
--spice ~/FreePDK45/osu_soc/lib/source/netlists/AND2X1.pex.netlist \
--cell AND2X1 \
--output /tmp/and2x1.lib
Characterize multiple cells in the same run:
lctime --liberty ~/FreePDK45/osu_soc/lib/files/gscl45nm.lib \
--include ~/FreePDK45/osu_soc/lib/files/gpdk45nm.m \
--output-loads "0.05, 0.1, 0.2, 0.4, 0.8, 1.6" \
--slew-times "0.1, 0.2, 0.4, 0.8, 1.6, 3.2" \
--spice ~/FreePDK45/osu_soc/lib/source/netlists/*.pex.netlist \
--cell INVX1 AND2X1 XOR2X1 \
--output /tmp/invx1_and2x1_xor2x1.lib
Cell recognition
Cell types can be recognized automatically such that only a minimal liberty file needs to be supplied.
cd examples
lctime --liberty template.lib \
--analize-cell-function \
--include gpdk45nm.m \
--spice INVX1.pex.netlist \
--cell INVX1 \
--output-loads "0.05, 0.1, 0.2, 0.4, 0.8, 1.6" \
--slew-times "0.1, 0.2, 0.4, 0.8, 1.6, 3.2" \
--output invx1.lib
Sequential cells
Characterization of sequential cells involves finding hold, setup, removal and recovery constraints.
For an example see examples/run_example_flip-flop.sh
.
Visualization
Vizualize the result:
libertyviz -l /tmp/and2x1.lib --cell AND2X1 --pin Y --related-pin A --table cell_rise
Characterize a cell with differential inputs
Differential inputs can be specified in the liberty template with the complementary_pin
attribute.
Only the non-inverted pin should appear in the liberty file.
Differential pairs can also be recognized based on their naming. For example if pairs are named with suffixes _p
for
the non-inverted pin and _n
for the inverted pin:
lctime --diff %_p,%_n ...
Merging liberty files
lctime
will output a liberty file containing only one cell. The libertymerge
command allows to merge this kind of
output file back into the liberty template.
The following example will take base_liberty.lib
as a template and update its cell
entries with the data found in
the liberty files in the characterization
directory.
libertymerge -b base_liberty.lib \
-o output_liberty.lib \
-u characterization/*.lib
This approach allows to run characterization runs of multiple cells independently and in parallel (e.g using make
).
Recognize a cell
lctime
can recognize the boolean function of cells based on the transistor network. Besides combinational functions
also memory-loops can be found and abstracted into latches or flip-flops.
The sp2bool
command can be used to analyze cells and dump information about their behaviour. This can be useful for debugging and verification.
Example:
# Analyze a combinational cell.
sp2bool --spice ~/FreePDK45/osu_soc/lib/files/cells.sp --cell NAND2X1
# Analyze a flip-flop with asynchronous set and reset signals.
sp2bool --spice ~/FreePDK45/osu_soc/lib/files/cells.sp --cell DFFSR
For cells with differential inputs the --diff
argument must be used to specify differential pairs.
Debugging
Options for increasing debugging information:
--debug
: increase verbosity. Will also show the path to generated SPICE files.--debug-plots
plot the waveforms of all simulations to a file. Slow but sometimes useful.- Enable very verbose trace log: set the
DEBUG_LCTIME
environment variable toyes
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