Precise timing in Visual Basic 6 program - Interrupts??? (for the experts)

Posted on 2007-11-22
Last Modified: 2012-08-14
Here is one for the real experts...

I have a gadget that measures a value which must be continuously updated in a very smooth scrolling graph.

I have to scroll a graph across a screen (pixel by pixel) displaying a graphical representation of real-time data I am measuring.  
I have been able to accomplish it... kind of.

The original programming is in VisualBasic6

The program monitors real-Time data (data input to PC is smooth)
The problem I am faced with is displaying the data without 'hick-ups' in the smooth scrolling graphs I create.

I have to display a scrolling (constantly Updated) picture  at a pre-selected Update Rate without allowing the screen to pause or jump.
AND The updates must be at displayed at precise (selectable) times.  
Current solution:
In order to make the Scrolling smooth I have chosen to Scroll all the pixels across the screen at every 'update' using BitBlt function.  
I simply add a new pixel Line at the beginning and Remove the last pixel Line from the display. (i.e. I am adding one pixel line and moving the existing graph (picture) up by one pixel line) This gives the appearancee of a nice, smooth scrolling graph.

I am willing to work with timer interrupts or anything else that would fix the problem.

I now have to add a print function so I don't like two thing in my current solution.  

Here is the Pseudo-code for my current solution.

'All setup stuff done....

DelayTime = ...(read DelayTime setting)
   'the value 'DelayTime' is what determines the Scrolling Speed  
   ' (each graph line update is simply timed by waiting until the for - next loop counts down)
   For delayCount = 1 to DelayTime
   'the Scroll Speed may have been changed at any time so i read the value every loop.
   DelayTime = ...(check to see if DelayTime was updated since last loop)
   'Then I Read a new value from my gadget so I can add to the next reading to the scrolling graph display.
   NewReading = input value
   'I then call a function to change the value into a representative pixel line for the next graph update
   Call makeGraph(NewReading)
   'Now I BitBlt the entire existing graph (picture box) over by one pixel and add the new pixel line to the beginning of the graph
   Call BitBlt routines to update graph...
   I need to add a 'Print Graph' function here...
   'Check for EscKey which indicated someone wants to end scrolling graph.
   ' (the program will continue scrolling data until this happens)
   read Esc - If Pressed then jump to Getout:
    Out of scroll display loop now....

This works great without the new 'Print Function' - When I add the print function I now have a hick-up during scrolling while the 'print function makes a copy of the current Picture box (I am actually printing to a file, not a printer).  I may need to fix this with an interrupt.  This ISR would have to have a higher priority then the Print function to smoothly to update the graph.

I know I said the current solution works great and it does 'functionally'.  The problem is that the CPU runs at 100% usage because of the For Next loop.  The Interrupt solution would fix that too (I think)  I would really like to find a way to time this loop w/o burning up the processor.

Unfortunately, I can't use the built-in Timer function because I need to be able to adjust the scroll speed of about 3 millisecond increments. (Timer function has approx 17ms increments).. Too slow dag nabit!

Anybody have an interrupt solution that would preempt the Print function? (maybe based on the 8251 hardware timer chips)

Thank You for your help!
Question by:dannyhop
Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people just like you are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
1 Comment

Accepted Solution

Taconvino earned 500 total points
ID: 20367615

That should have a resolution of 1ms, but the Sleep() function may add a 5ms error to that.  Still, very close.  I'm not sure how this could prevent your "hick-up" problem, as it is probably caused by the IO process.  Maybe I didn't understood your question completely... you need to lower the IO (print) process priority?


Featured Post

Online Training Solution

Drastically shorten your training time with WalkMe's advanced online training solution that Guides your trainees to action. Forget about retraining and skyrocket knowledge retention rates.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Suggested Solutions

Title # Comments Views Activity
Hide vba in gp 7 117
Passing a Text Box name to a Sub 6 102
Macro Excel - Multiple If conditions 2 88
Help with retrieving partial value from a column using VB.NET 4 53
Introduction I needed to skip over some file processing within a For...Next loop in some old production code and wished that VB (classic) had a statement that would drop down to the end of the current iteration, bypassing the statements that were c…
Background What I'm presenting in this article is the result of 2 conditions in my work area: We have a SQL Server production environment but no development or test environment; andWe have an MS Access front end using tables in SQL Server but we a…
Get people started with the utilization of class modules. Class modules can be a powerful tool in Microsoft Access. They allow you to create self-contained objects that encapsulate functionality. They can easily hide the complexity of a process from…
Show developers how to use a criteria form to limit the data that appears on an Access report. It is a common requirement that users can specify the criteria for a report at runtime. The easiest way to accomplish this is using a criteria form that a…

726 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question