+ /*
+ * These "position" values point to after the event (end of
+ * capture data, trigger condition matched). This is why they
+ * get decremented here. Sample memory consists of 512-byte
+ * chunks with meta data in the upper 64 bytes. Thus when the
+ * decrements takes us into this upper part of the chunk, then
+ * further move backwards to the end of the chunk's data part.
+ */