Emergency stop during Wait

Question

Hi.
I have a process that runs through several stages in sequence. Each stage needs to wait for ~ 5 minutes before starting the next stage. There isn't really any "logic" involved; it just moves from one to the next until the end. However, I want to implement an Emergency Stop that will exit the current stage and perform some shutdown procesures. I am using a state machine inside a while loop to handle each step but I can't figure out how to exit immediately. When I press the "Stop" button, it continues through the current step, then next step and finally exits two steps later.
Here is a dummy example of my structure:
Any suggestions?
thanks,
jason
Attachments:
state_machine_interupt_example.vi ‏22 KB

Answer 1

If you are frequently adding features to your program, you definitely need to investigate the various flavors of state machines and producer/consumer architectures.  The two are not mutually exclusive.  In fact they work well together.  Key advantages are robust performance and ease of modification.  There are examples which ship with LV and many, many postings on the Forums about these topics.
For multiple independent timing I like to use a Timeout value for each task which needs timing.  When the task starts, read the current tick count and add the timeout delay (or wait) value in milliseconds, and put the resulting Task[i] Timeout value (= tick count when task should stop) into a shift register.  Each time through the loop the current tick count is compared to all of the Task[i] Timeout values.  For any task where the tick count equals or exceeds the Timeout value, stop the task.
Any process which takes longer than the minimum resolution of the timing for ANY task needs to be put into a parallel loop or decomposed into small enough pieces to allow the interruption if a timeout occurs.
Lynn