3. • Feedback loops impose inherent fundamental
lower bound on the achievable iteration or
sample period
• IB is a characteristics of the representation of an
algorithm in the form of a DFG
• Different representation of the same algorithm –
different IB
• Not possible to achieve iteration period less than
the iteration bound
• Two techniques
– Longest path matrix
– Minimum cycle mean method
4.
5. • Iteration of a node is the execution of the node
exactly once
• Iteration of the DFG is the execution of each node
in the DFG exactly once
• Precedence constraints
• Intra-iteration
• Inter-iteration
• Critical path
• The path with the longest computation time among all
paths that contains zero delays
6. Critical path is the minimum computation time
for one iteration of the DFG
DFG – recursive and nonrecursive
Recursive DFG has a fundamental limit on how
fast the DSP program can be implemented in
hardware – the limit is called iteration bound
7. LOOP BOUND
• A loop is a directed path that begins and ends at
the same node
• loop/ cycle
• Loop bound – lower bound on the loop
computation time
• Loop bound of the j-thloop: defined as Tj/Wj,
where Tjis the loop computation time & Wj is the
number of delays in the loop
• Number of loops in a DFG can be exponential
with respect to the number of nodes
