Independent timer/dwell within an object

[JeffT]

I have created an AXIS object in my motion control project. I am commanding
an axis to move to a certain position. I need to asynchronously dwell for
some period of time then check to make sure the axis is were it should be.
If not, I need to post a "time out" alarm. I will command multiple axis'
to move at once and, depending on the distance to move, they will have different
time out values. How can I start a timer within an object without blocking
the processor. I tried a loop with DoEvents and sleep but this didn't work.
The last axis commanded to move needs to finish before previous axis' can
continue.

[Dick Grier]

Hi,

What you want to do is to use a Timer (object). If the standard VB Timer
resolution (55 mS) is sufficient, then you can place on a form, instantiate
it from within your class, and use the Timer event that it generates
asynchronously.

However, you may get more out of using a high-resolution timer like Karl
Peterson's (www.mvps.org/vb and www.mvps.org/ccrp -- these are two different
implementations, based on the same basic concepts).

--
Richard Grier (Microsoft Visual Basic MVP)
Hard & Software
12962 West Louisiana Avenue
Lakewood, CO 80228
303-986-2179 (voice)
303-986-3143 (fax)
Author of Visual Basic Programmer's Guide to Serial Communications, 2nd
Edition ISBN 1-890422-25-8 (355 pages).
For information look on my homepage at http://www.hardandsoftware.net.
Use the Books link to order. For faster service contact the publisher at
http://www.mabry.com/vbpgser.

[martin.rydman]

Hi Jeff!

You can also use this technique (I've got it from Dan Appleman)

In a bas-module, put this:


Attribute VB_Name = "mdlTimer"
'****** Project FileListServer ActiveX EXE ***********
' mdlTimer.bas
' (Thanks do Dan Appleman)
'
'This is how we can launch a long operation. We use a Win32 timer, set it
to
'trigger a call to a callback procedure after 1 millisecond, and in the
'callback procedure (TimerProc in this example), we launch the actual
'long operation.
'The StartTimer sub takes an object on which the long operation
'is called (mobjCallingObject.GetFileArray).

Option Explicit

Public Declare Function SetTimer Lib "user32" (ByVal hwnd As Long, ByVal
nIDEvent As Long, ByVal uElapse As Long, ByVal lpTimerFunc As Long) As Long
Public Declare Function KillTimer Lib "user32" (ByVal hwnd As Long, ByVal
nIDEvent As Long) As Long

Private mobjCallingObject As CFileList
Private TimerID&

Public Sub StartTimer(CallingObject As CFileList)
Set mobjCallingObject = CallingObject
TimerID = SetTimer(0, 0, 1, AddressOf TimerProc)
End Sub

'This is the callback procedure that sets of the parser
Public Sub TimerProc(ByVal hwnd&, ByVal msg&, ByVal id&, ByVal currenttime&)
Call KillTimer(0, TimerID) 'This is for one-off launching
'You might want to keep the timer
'return here regularly
TimerID = 0
mobjCallingObject.GetFileArray
Set mobjCallingObject = Nothing
End Sub



In your calling class (the one to containing the asynchronous method):

'This is the trigger for the asynchronous service. It only sets of a
'Win32 timer that in turn will set of the actual parser
Public Sub GetAsynchFileArray(Path As String)
mstrPath = Path
StartTimer Me
End Sub

'This method is called from the callback-procedure in mdlTimer
Friend Function GetFileArray()
'Your asyncronous operation
End Function


This way, you won't have to add a form to your server to hold the timer.
Otherwise it's the sam idea as the previous posters.


HTH

/Martin