Start the openlane tutorial

Author: mguthaus

openlane.md

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+# Running an example design
+
+This assumes that the smoke test runs and you've [installed OpenLane properly](installation.md).
+
+You can run an example design called "SPM" by running:
+```
+openlane --run-tag foo --run-example spm
+```
+which will download the design, all technology files, and completely implement the design. Once
+done, all of the files are in the "spm" subdirectory. The run logs and outputs of the tools are in
+a directory with the current date and time like "spm/runs/RUN_2024-12-12_11-58-38".
+
+Once you've run once, you can enter the directory and see the files:
+- config.yaml: The configuration of the design.
+- src: The directory with the Verilog source files.
+- run: The directory containing all runs, one per directory.
+- verify: The verification directory with Verilog test benches.
+
+If you want to run again, you can specify the config file as an argument to OpenLane:
+```
+cd spm
+openlane config.yaml
+```
+
+## Run directories and tags
+
+If you want to to specify a run name like "foo", you can add the "--run-tag foo" to a command. 
+This will put everything in "spm/runs/foo", but if you run again, you will either need to remove
+that directory to start over, or specify "--overwrite" on the command line:
+```
+openlane --run-tag foo config.yaml
+openlane --run-tag foo --overwrite config.yaml
+```
+
+
+## Viewing the final design
+
+The --last-tag option is also a shortcut for the last run directory. To view the last design in
+the OpenROAD GUI, you can run:
+```
+openlane --flow OpenInOpenROAD --last-tag config.yaml
+```
+and you should see the following:
+![Default SPM project in OpenROAD GUI](openlane/openroad_gui_spm.png)
+
+
+
+