add explanation in PinGen class

diff --git a/src/spec/interfaces.py b/src/spec/interfaces.py
index 03d7a2a9b1ea35679d71ed90ebedeaa1b75fcd92..e2cddba6b3e606d9279c1b1c553693591e8347f0 100644 (file)
--- a/src/spec/interfaces.py
+++ b/src/spec/interfaces.py
@@ -30,7 +30,11 @@ class PinGen(object):
         mux   : which column in the multiplexer
         start : the start of a subset of pins to be inserted
         limit : the end of the subset (or the number if start also given)
-        spec  : *EXTRA* pins to be inserted.
+        spec  : *EXTRA* pins to be inserted (at different implicit positions)
+
+        the pins are inserted with the suffix, starting from the
+        offset position using offs as the row and mux as the column,
+        and working in a constant increment down the rows.
 
         spec is slightly complicated, basically there's extra
         functions that we want to be on the same pin (but a different mux)