/sky130-hello-world

Minimal SKY130 example with self-checking LVS, DRC, and PEX

Primary LanguageMakefileApache License 2.0Apache-2.0

sky130-hello-world

The example is based around the minimum-size inverter from the SKY130 PDK. DRC is run on the GDS for that inverter, and then it is extracted for LVS and PEX. On the LVS front, the extracted SPICE netlist is compared to the netlist given in the PDK using netgen. On the PEX front, ngspice is used to run a transient simulation of the inverter with parasitic capacitances included. The regression tests also include some tests to make sure that DRC and LVS errors can in fact be detected, using the intentionally broken file inv1_bad.gds.

The full details for this example can always be found by examining the source code here, but the main functions are also summarized below.

Installing dependencies

Certain dependencies need to be installed before moving on to the SKY130-specific tools.

sudo apt-get install m4 tcsh csh libx11-dev tcl-dev tk-dev libcairo2-dev libncurses-dev libglu1-mesa-dev freeglut3-dev mesa-common-dev ngspice

MAGIC VLSI Layout

Magic is a dependency to install open_pdks.

Installation instructions: http://opencircuitdesign.com/magic/

Source found here: https://github.com/RTimothyEdwards/magic

PDK

Next, The sky130 PDK must be installed.

This PDK is installed via open_pdks.

Installation instructions: http://opencircuitdesign.com/open_pdks/

Source found here: https://github.com/RTimothyEdwards/open_pdks

Installing tools

Running make install-tools installs the following tools locally: magic, netgen, ngspice, xschem.

If the PDK install location was manually set, update the PDKSPATH and/or PDKNAME at the top of the Makefile before installing.

Launching tools

Because the tools are not added to the shell path, Make targets were added as shourtcuts to launch them:

make launch-xschem

make launch-ngspice

make launch-magic

make launch-netgen

The following syntax is used to pass additional arguments into the programs:

make launch-<TOOL> args=<ADDITIONAL_ARGS>

For example: make launch-ngspice args=--version will launch NGSPICE, print the version, and exit.

Running DRC

Launch Magic, and enter the following commands into the Magic console to count up the number of DRC violations. For some reason, the final line says that there are zero DRC errors, even if previous lines show errors.

% gds read inv1.gds
% load sky130_fd_sc_hd__inv_1
% drc catchup
% drc count

To confirm the DRC check, you may replace the gds file in the first line with inv1_bad.gds. This file is expected to have DRC errors.

Running PEX

Launch Magic, and enter the following commands into the Magic console to generate a netlist of the example cell with Parasitic Extraction.

% gds read inv1.gds
% load sky130_fd_sc_hd__inv_1
% extract all
% select top cell
% port makeall
% ext2spice lvs
% ext2spice cthresh 0.01
% ext2spice rthresh 1
% ext2spice subcircuit on
% ext2spice -o pex_inv1.spice

The output of these commands will be pex_inv1.spice

Running LVS

The following magic TCL script reads in a GDS and extracts it to an LVS-ready netlist.

% gds read inv1.gds
% load sky130_fd_sc_hd__inv_1
% extract all
% ext2spice lvs
% ext2spice subcircuits off
% ext2spice -o lvs_inv1.spice
quit

The output of these commands will be lvs_inv1.spice

LVS can be run to compare the design netlist with the extracted netlist using netgen:

make launch-netgen args=-batch\ lvs\ "inv1.spice\ sky130_fd_sc_hd__inv_1"\ "lvs_inv1.spice\ sky130_fd_sc_hd__inv_1"\ <PDKPATH>/libs.tech/netgen/sky130A_setup.tcl

Running SPICE simulations with NGSPICE

The example simulation can be run with this command:

make launch-ngspice args=./my_nmos_test.spice

Open the example schematics with XSCHEM

When launching XSCHEM without argumenst (make launch-xschem), it will open the default SKY130 example schematic.

To open one of the example sim, select one of the yellow rectangles on the left (ex. "test_nmos") and press 'e' to enter the schematic.

Launch a simulation from XSCHEM

XSCHEM can be integrated with NGSPICE to simulate the current schematic.

To generate a SPICE netlist from the current schematic, press the "Netlist" button in the upper right of the XSCHEM window. The netlist will appear as <SCHEMATIC_NAME>.spice in the project directory.

To launch the simulation with NGSPICE, press the "Simulate" button to the right of the "Netlist" button. However, NGSPICE is not added to PATH by default. The PATH to the simulator can be manually set from the XSCHEM gui. Under the "Simulation" dropdown, choose "Configure simulators and tools" In the top-center box replace the command with this one:

$terminal -e '`pwd`/tools/ngspice-install/bin/ngspice -i "$N" -a || sh'

Now, XSCHEM will use the ngspice we have installed for our project.

(This can also be configured by editing ~/.xschem/simrc)

Acknowledgements