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.
# Clone this repository.
git clone https://codeberg.org/librecell/lctime
cd lctime
# Install
./install_develop.sh
# Run tests
cd tests
./run_tests.sh
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 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
Characterization of sequential cells involves finding hold, setup, removal and recovery constraints.
For an example see examples/run_example_flip-flop.sh
.
Vizualize the result:
libertyviz -l /tmp/and2x1.lib --cell AND2X1 --pin Y --related-pin A --table cell_rise
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 ...
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
).
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.
Enable very verbose trace log: set the DEBUG_LCTIME
environment variable to yes