Added documentation for error message format

nengo_loihi/snips/nengo_learn.c

@@ -6,6 +6,26 @@ int guard_learn(runState *s) {
     return 1;
 }
 
+/***********************************************************************
+ * Handles passing learning information to the correct learning rules
+ * to implement PES learning on Loihi.
+ *
+ * The required data is passed to this snip from the standard nengo_io
+ * snip via the userData structure.  The data format is as follows:
+ *
+ *  0:  n_errors: the number of learning signals.  This is the same as the
+ *      number of Connections in the original Nengo model that terminate on
+ *      a conn.learning_rule.  
+ *
+ *      This indicates how many copies of the following block there will
+ *      be.
+ * -------------
+ *  1:  core: The core id for the weights of the first learning connection
+ *  2:  n_vals:  The number of dimensions of the error signal
+ *  3..3+n_vals: The error signal (multiplied by 100, rounded to an int and
+ *                                 clipped to -100,100)
+ * -------------
+ */
 void nengo_learn(runState *s) {
     int offset = 1;
     int n_errors = s->userData[0];