This work examines the complexity of scheduling for high level synthes
is. It has been shown that the problem of finding the minimum time sch
edule for a set of chains of operations of two types using two process
ors, one of each type, is NP-complete. However, for two chains only, a
polynomial time algorithm can been obtained for scheduling with two p
rocessors. The problem of scheduling a rooted binary tree of two opera
tion types on two processors, one of each type, has been shown to be N
P-complete. It has also been proved that absolute approximations for s
chedule length minimization or processor minimization are NP-complete.
A related resource constrained scheduling problem has also been shown
to be NP-hard.