Re: Peculiar SNL behaviour

[Eric Norum <eric@norum.ca>]

Yes, the sequencer has no 'watchpoint' mechanism on which to wait between scanning the list if 'when' statements.  I have a feeling that handling this in a general way would be akin to solving the 'halting' problem.

Anyhow, the sequencer does provide events to be used in such state set synchronization applications.


On Dec 31, 2011, at 3:43 PM, S. Stein wrote:

> Last question for 2011 from me - I promise!
> 
> I have a sequence program with a couple of state sets running. To enable a state transition in one state-set, I set (or reset) a variable (which does not correspond to an EPICS PV) - see example below. here is my issue: I cannot seem to get the 'wait' state in stateset 2 to fire off without toggling 'pv1'.  
> 
> Here's what I do: assuming the PV  'epics:pv1C' is set to a BO record, I run the IOC. I see the console messages for the state sets firing off. I then set the VAL of 'epics:pv1C' to '1' and see that the ioc console responds with "PV Change state". After 2 seconds delay the internal variable 'seqFlag' is set to true, which _should_ (at least I think) fire off the 'wait' state in the second set, thus printing "Wait State Reached" on the IOC console. It does not. I have to set the PV 'epics:pv1C' to '0' and back to '1' to get the state transition to fire.
> 
> I don't think this behavior is appropriate - what say the community?
> 
> 
> Contrived example:
> 
> /* epics variables */
> short pv1; assign pv1 to "epics:pv1C"; monitor pv1;
> /* sequencer variables */
> short seqFlag = FALSE;
> 
> ss set1 {
> state init {
>  entry {
>   printf("Set 1 started\n");
>  }
>  when (pv1 == TRUE);{
>   printf("PV Change state\n");
>   } state seqHold
>  }
> 
> state seqHold {
>  when(delay(2)) {
>   seqFlag = TRUE;
>  } state done
> 
> state done {
>  when(FALSE) {
>  } state init
> }
> }
> 
> ss set2 {
> state init {
>  when(Delay(1){
>   printf("Set 2 started\n");
>  } state wait
> }
> 
> state wait {
> when ((pv1 == TRUE) && (seqFlag == TRUE)) {
>   printf("'Wait state' reached\n");
>  } state done
> 
> state done {
>  when(FALSE) {
>  } state init
> }
> }
> 

-- 
Eric Norum
eric@norum.ca