Merge pull request #480 from SpiNNakerManchester/reduce_overhead_data…

…_spec_colours

Reduce overhead data spec colours

pacman/utilities/utility_calls.py

@@ -145,13 +145,17 @@ def get_n_bits(n_values):
     return int(math.ceil(math.log2(n_values)))
 
 
-def get_field_based_keys(key, vertex_slice):
+def get_field_based_keys(key, vertex_slice, shift=0):
     """ Translate a vertex slice with potentially multiple dimensions into
         a list of keys, one for each atom of the vertex, by putting the values
         into fields of the keys based on the shape of the slice.
 
     :param int key: The base key
     :param Slice vertex_slice: The slice to translate
+    :param int shift:
+        The left shift to apply to the atom key before adding to the key. Can
+        be used to make space for additional information at the bottom of the
+        key.
     :rtype: list(int)
     """
 
@@ -173,19 +177,27 @@ def get_field_based_keys(key, vertex_slice):
     # get the key
     keys = numpy.sum(numpy.left_shift(coords, shifts), axis=1)
 
+    # Do any final shifting as required (zero shift is valid but does nothing)
+    if shift:
+        keys = numpy.left_shift(keys, shift)
+
     # The final result is the above with the base key added
     return keys + key
 
 
-def get_field_based_index(base_key, vertex_slice):
+def get_field_based_index(base_key, vertex_slice, shift=0):
     """ Map field based keys back to indices
 
     :param int base_key: The base key
     :param Slice vertex_slice: The slice to translate
+    :param int shift:
+        The left shift to apply to the atom key before adding to the key. Can
+        be used to make space for additional information at the bottom of the
+        key.
     :rtype: dict(int,int)
     """
     # Get the field based keys
-    field_based_keys = get_field_based_keys(base_key, vertex_slice)
+    field_based_keys = get_field_based_keys(base_key, vertex_slice, shift)
 
     # Inverse the index
     return {