Deadlock is one of the most serious problems in concurrent
programming.  Recently, Kobayashi proposed a static type system for a
process calculus which ensures that communication over some special
channels never causes deadlock.  However, since the class of such
channels was fixed ad hoc by the type system, the deadlock-free
fragment of the calculus was limited and the essence of the type
system was not so clear.

In this paper, we generalize his type system in order to extend the
deadlock-free part of his calculus.  For that purpose, we annotate
each channel type with an expression called a _usage_, which specifies
how the channel _may_ and _must_ be used.  It is automatically checked
by the type system that the usage does not cause deadlock and that the
channel is actually used along the specification.  As a result, the
deadlock-freedom property is treated more uniformly and guaranteed
more extensively.