question about state notation language logic for when() with delay

[Jay Steele <jsteele@xradia.com>]

Hi EPICS folks,

  For the state notation language, the when statement is mostly straightforward in that the code following the when statement occurs when the logical _expression_ inside the when statement is true. However, I'm a little confused by the delay function in a when statement because something needs to start and monitor the timer for the delay. I need to understand this delay logic better for a EPICS robot control application I'm working on. When does the timer start and how is it monitored for the delay? For example, if I use the following when statement for a state transition,

 

when(A==1 && delay(1.0) && B==1),

 

  does the timer for the delay only start and continue after the A==1 logical condition is met and, after the delay is done, then it checks the B==1 logical condition? Thus, does the order of logical conditions in the when statement make a difference so that when(delay(1.0) && A==1 && B==1) behaves differently? Here is one possible interpretation of when(A==1 && delay(1.0) && B==1):

 

time     A     B    transition

-----    ---    ---   ----------

0         0      0    none

1         0      0    none

2         1      0    none

2.5      1      1    none

3         1      0    none

4         1      1    yes

 

  Or, does the timer for the delay only start and continue after both the A==1 and B==1 conditions are satisfied? In which case, we get the following result for when(A==1 && delay(1.0) && B==1):

 

time    A        B    transition

-----   ---      ---    ----------

0        0        0       none

1        0        0        none

2        1        0       none

2.5     1        1       none

3        1        0       none

4        1         1      none

5        1         1      yes

 

Or does the timer for the delay start as soon as the state containing the when statement becomes active and just continue? In this case, the results would be as follows for when(A==1 && delay(1.0) && B==1).

 

time    A     B    transition

-----   ---   ---   ----------

0        0      0      none

1        0      0      none

2        1      0      none

2.5     1      1      yes

 

  I will test these different situations out, but I wanted to understand the underlying logic intent so that my SNL implementation will not break with future software versions.

 

Cheers,

Jay Steele

Xradia Corporation

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