add readme

README.md

@@ -1,6 +1,109 @@
-snarl
+snarl README
-=====
+============
 
 Layout connectivity checker.
 
-TODO: Documentation and examples!
+`snarl` is a python package for checking electrical connectivity in multi-layer layouts.
+
+It is intended to be "poor-man's LVS" (layout-versus-schematic), for when poverty
+has deprived the man of both a schematic and a better connectivity tool.
+
+- [Source repository](https://mpxd.net/code/jan/snarl)
+- [PyPI](https://pypi.org/project/snarl)
+
+## Installation
+
+Requirements:
+* python >= 3.9 (written and tested with 3.10)
+* numpy
+* pyclipper
+
+
+Install with pip:
+```bash
+pip3 install snarl
+```
+
+Alternatively, install from git
+```bash
+pip3 install git+https://mpxd.net/code/jan/snarl.git@release
+
+
+## Example
+See `examples/check.py`. Note that the example uses `masque` to load data.
+
+```python3
+from pprint import pformat
+from masque.file import gdsii, oasis
+import snarl
+import snarl.interfaces.masque
+
+# Layer definitions
+connectivity = {
+    ((1, 0), (1, 2), (2, 0)),   #M1 to M2 (via V12)
+    ((1, 0), (1, 3), (3, 0)),   #M1 to M3 (via V13)
+    ((2, 0), (2, 3), (3, 0)),   #M2 to M3 (via V23)
+    }
+
+
+cells, props = oasis.readfile('connectivity.oas')
+topcell = cells['top']
+
+polys, labels = snarl.interfaces.masque.read_cell(topcell, connectivity)
+nets_info = snarl.trace_connectivity(polys, labels, connectivity)
+
+print('\nFinal nets:')
+print([kk for kk in nets_info.nets if isinstance(kk.name, str)])
+
+print('\nShorted net sets:')
+for short in nets_info.get_shorted_nets():
+    print('(' + ','.join([repr(nn) for nn in sorted(list(short))]) + ')')
+
+print('\nOpen nets:')
+print(pformat(dict(nets_info.get_open_nets())))
+```
+
+this prints the following:
+
+```
+Nets ['SignalD', 'SignalI'] are shorted on layer (1, 0) in poly:
+ [[13000.0, -3000.0],
+ [16000.0, -3000.0],
+ [16000.0, -1000.0],
+ [13000.0, -1000.0],
+ [13000.0, 2000.0],
+ [12000.0, 2000.0],
+ [12000.0, -1000.0],
+ [11000.0, -1000.0],
+ [11000.0, -3000.0],
+ [12000.0, -3000.0],
+ [12000.0, -8000.0],
+ [13000.0, -8000.0]]
+Nets ['SignalK', 'SignalK'] are shorted on layer (1, 0) in poly:
+ [[18500.0, -8500.0], [28200.0, -8500.0], [28200.0, 1000.0], [18500.0, 1000.0]]
+Nets ['SignalC', 'SignalC'] are shorted on layer (1, 0) in poly:
+ [[10200.0, 0.0], [-1100.0, 0.0], [-1100.0, -1000.0], [10200.0, -1000.0]]
+Nets ['SignalG', 'SignalH'] are shorted on layer (1, 0) in poly:
+ [[10100.0, -2000.0], [5100.0, -2000.0], [5100.0, -3000.0], [10100.0, -3000.0]]
+
+Final nets:
+[SignalA, SignalC__0, SignalE, SignalG, SignalK__0, SignalK__2, SignalL]
+
+Shorted net sets:
+(SignalC__0,SignalC__1,SignalD,SignalI)
+(SignalK__0,SignalK__1)
+(SignalG,SignalH)
+(SignalA,SignalB)
+(SignalE,SignalF)
+
+Open nets:
+{'SignalK': [SignalK__0, SignalK__2]}
+```
+
+## Code organization
+
+The main functionality is in `trace_connectivity`.
+Useful classes, namely `NetsInfo` and `NetName`, are in `snarl.tracker`.
+`snarl.interfaces` contains helper code for interfacing with other packages.
+
+