External State

1
External State

• Kerry Barnes
• Gedae, Inc.
• www.gedae.com
• 856-231-4458

2
Controlling Segment Reset

• During Segment Reset all boxes call their Reset
  methods
• All Primitive Local state variables are set to
  their initial state
• What if the algorithm requires state to be
  persistent between segments?
• Done using external state

3
Persistent State

• Moving state out of subgraph controlled by
  segmenter makes the state persistent across
  segment boundaries

segmenter
proc1
in
out
in
out
S
State input S
state
K
out
4
Illegal graph

• External state variables cannot be shared between
  primitives
• Sharing would possibly change the algorithm when
  there is a
• Change in granularity
• Change in primitive firing order

segmenter
proc1
proc2
in
out
in
out
in
out
S
S
State inputs
state
K
out
5
Legal graph

• One writer and multiple readers of state can be
  implemented by having state input box output
  state values

segmenter
proc1
proc2
in
out
in
out
in
out
s
S
s
State input
state
Value follows state input
K
out
6
Controlling Reset Level

• State variable is reset by toplevel segmenter but
  not second level segmenter

segmenter
proc1
segmenter
in
out
in
out
in
out
S
State input S
state
K
out
7
Low Pass Filter with Internal State Informational
and Data Fields

• Name lpf
• Type static
• Input
• stream float in
• float A
• Local
• float fb
• Output
• stream float out

8
Low Pass Filter with Internal State Methods

• Reset
• fb 0
• Apply
• int i
• out0 fb A(in0-fb)
• for (i1 iltgranularity i)
• outi outi-1 A(ini- outi-1)
• fb outgranularity-1

9
Low Pass Filter with State Input

• Name lpf_s
• Type static
• Input
• stream float in
• float A
• state float fb
• Output
• stream float out
• Apply
• int i
• out0 fb A(in0-fb)
• for (i1 iltgranularity i)
• outi outi-1 A(ini-outi-1)
• fb outgranularity-1

Removed Reset and Local state variable fb and
replaced with state input fb.
State input fb declared with state keyword
Previous value of state variable can be used in
the Apply method
Apply method must set the final value of the
state variable before it exits
10
State Primitive

• Name float_state
• Type state
• Input
• float K
• Output
• float out
• Init
• K 0
• Reset
• out K

Type of box is state
May have input parameters
Outputs are the external state variables that can
be connected to primitive state inputs
Reset method called at segment Reset
11
Example 1

• Internal state interior to subgraph gives
  identical results to normal lpf box
• Transients are still seen on segment boundaries

12
Example 1 Trace Table

• The float_state Reset method is called at the
  beginning of every segment

13
Example 2 Trace Table

• The float_state box is only Reset at the
  beginning of flowgraph execution

14
Example 2

• Moving state out of filterS box causes it to be
  persistent between segment boundaries
• Transients no longer observed on segment
  boundaries

15
Example 3

• Filter state reset at toplevel segment boundaries
• Not reset by second level segment boundaries

16
Example 3
17
Exercise 1

• Load graph
• gedae file training/segmentation/lect5/Exercise1
  pa default gr default tr
• Run graph and observe output
• Change filterX1.integrate to use external state
• Add float_state box to filterX1 and connect to
  integrate
• Run graph and observe similar behavior
• View trace table and note when the float_state
  resets occur

18
Exercise 2

• Load graph
• gedae file training/segmentation/lect5/Exercise2
  pa default gr default tr
• Run graph and observe output
• Replace filterX2.integrate with integrate box
  created in previous example
• Add an input S to filterX2 and connect to the
  integrate state

19
Exercise 2(continued)

• Add float_state box to toplevel graph and connect
  to filterX2ltS
• Run graph and observe no reset on segment
  boundaries
• View trace table and note when the float_state
  resets occur