Experimental Physics and
Industrial Control System

"Brian McAllister" <[email protected]> · Thu, 02 May 2002 19:59:04 -0400

>>> On 5/2/2002 at 13:42:32 -1000, Ian A Smith wrote:

  > the snc manual says that the delay() function can only be used inside a
  > when expression.  Is this really true?  Isn't it just a finction that
  > returns true or false?  I want to use it inside a for statement.

Sorry, you can't do that.

When a state containing delay() clauses is entered, a timer is started for
each one (in the context of the main sequencer task, I think) which is then
checked by the sequencer along with any other when() tests in that state.

There is a function that returns true when the timer expires, and you could
potentially make use of this mechanism by writing escaped C code, but you
would have to be very careful.

Keep in mind that if you do anything in a when() clause that blocks
execution, you will suspend *all* sequencers for that time.  Using
taskDelay() will allow other tasks to continue, but not other sequencers.

Looking at the generated C code may make it clearer how this works.

----
Brian McAllister                    Controls Programmer/Beam Physicist
[email protected]                        MIT-Bates Linear Accelerator
(617) 253-9537                                           Middleton, MA

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System