Added clarification on retiring inferable calls in blocks when itype …

…width is 3

ingressPort.adoc

@@ -306,7 +306,10 @@ block.
 *itype* can be 3 or 4 bits wide. If _itype_width_p_ is 3, a single code
 (6) is used to indicate all uninferable jumps. This is simpler to
 implement, but precludes use of the implicit return mode (see
-<<sec:implicit-return>>), which requires jump types to be fully classified.
+<<sec:implicit-return>>), which requires jump types to be fully classified.  
+Note that when _itype_width_p_ is 3 *itype* is 0 used for inferrable calls.  
+However, inferrable calls must still be the final instruction retired in a 
+block, otherwise the block would not be comprised of contiguous instructions.
 
 Whilst *iaddr* is typically a virtual address, it does not affect the
 encoder's behavior if it is a physical address.