Dynamic Dataflow Graphs - Signal Processing Systems - page 899

c

a

1

Actor (Sub)Scenario E (kCycles)

d d

VLD IDCT

P 0 0

VLD

All except P 0 40

a

d

1

P 0 0

IDCT

b

All except P 0 17

1

1 e

c c

1

1

MC

I , P 0 0

1 1

FD

1

RC

P 30 90

1 1

P 40 145

1

1 3

P 50 190

MC

P 60 235

P 70 265

b

Rate (Sub)Scenario
I 0 P x
a 00 1
b 00 x
c 99 1 x
d 10 1
e 99 0 x
x ∈{ 30 , 40 , 50 , 60 , 70 , 80 , 99 }

P 80 310

P 99 390

I 350

P 0 0

P 30 , P 40 , P 50 250

RC

P 60 300

P 70 , P 80 , P 99 320

FD All 0

Fig. 5 Modeling the MPEG-4 decoder with SADF. ( a ) Actors and channels; ( b ) parameterized
rates; ( c ) worst-case execution times

control the behavior of actors through scenarios . 2 Moreover, data channels (solid
edges) and control channels (dashed edges) are distinguished. Control channels
communicate scenario-valued tokens that influence the control flow. Data tokens do
not influence the control flow. The availability of tokens in channels is shown with
a dot. Here, such dots are labeled with the number of tokens in the channel. The
start and end points of channels are labeled with production and consumption rates
respectively. They refer to the number of tokens atomically produced respectively
consumed by the connected actor upon its firing . The rates can be fixed or scenario-
dependent, similar as in PSDF. Fixed rates are positive integers. Parameterized
rates are valued with non-negative integers that depend on the scenario. The
parameterized rates for the MPEG-4 decoder are listed in Fig. 5 b . A value of
0 expresses that data dependencies are absent or that certain operations are not
performed in those scenarios. Studying Fig. 5 b reveals that for any given scenario,
the rate values yield a consistent SDF graph. In each of these scenario graphs,
detector FD has a repetition vector entry of 1 [ 70 ] , which means that scenario
changes as prescribed by the behavior of detectors may occur only at iteration
boundaries of each such scenario graph. This is not necessarily true for SADF in
general as discussed below.

2 In case of one detector, SADF literature may not show the detector and control channels explicitly.