Passing Variables Question

bgw56

My questions is as follows:
I have two objects running , one is sensing push button states, the other generating servo pulse timing in a repeat loop.
Is there a way to pass the button state info from the first object into the servo loop of the second while it running for motor control . I've considered passing control info using a pair of I/O pins. One outputting button states and the other being sensed inside the servo pulse timing loop. That seems like the hard way.What's the easy way?

Thanks !

Mike Green

The easy way is just to use a shared variable. You have a single shared variable (byte, word or long as needed) in your main program and you pass the address of this variable to first the push button object (where it's initialized), then the servo object (where it's referenced). The push button object just has to put useful information in it (like the button states) and the servo object can reference it.

Because it's a single byte / word / long and only one cog changes it (the button one), you don't need to use locks. If you needed more than one storage unit (like an array of words) or if the servo object had to change it, you might have to use locks, but not with the situation you've outlined.

bgw56

Hi Mike,
I've succeeded in passing variables between the two objects (button to servo) but never into the timing loop.

Your way sounds like just what I'm looking for.
Can you give me the how-to's of declaring and sharing variables the way you mentioned.
Also, how they can be changed and read by multiple objects.

Thanks
BW

bgw56

Mike,
I think I get it now. Just didn't know where to start.
Reading/writing Bytes of Main Memory (Syntax3) Manual P.167

Thanks
BW

Mike Green

I really can't make much more suggestions without using your code as a framework. How about posting it as attachments to a reply?

deSilva

How to dereference a pointer is not too obvious... The syntax is - "funny"

bgw56

Hi,
After a quick read of Byte and Dat,
Here is some code I tried as a test. I thought it might be possible to share the Dat array between objects.
It works when run in first object alone.

What I need to do in a nutshell : read a button in object 1. Pass that data into a running loop in object 2.
Object 2 could be as simple as stopping a flashing led.

Mike Green

Here's a simple example:

VAR
   long myData
   long stack[noparse][[/noparse]30]

PUB main | temp
   startOther(@myData) ' Pretend this is in another object

' --- the next loop could be in yet another object

   repeat
      ' read a button and put some value into temp
      long[noparse][[/noparse]@myData] := temp  ' Transfer the value to the shared variable

' --- pretend this is now another object

PUB startOther(pointer)
   long[noparse][[/noparse]pointer] := 0   ' Initialize the shared variable
   cognew(otherMethod(pointer),@stack) ' Launch the other cog and return

PRI otherMethod(pointer)
   if long[noparse][[/noparse]pointer] <> 0
      ' do something if non-zero
   else
      ' do something else if zero

deSilva

As your code was a little bit confusing I have simplified it:

OBJ                         
     PP : "Peek&Poke_B"     

PUB Button
  'Debug.start(31, 30, 0, 57600)
   repeat
        MyData[noparse][[/noparse] 0 ] := INA[noparse][[/noparse] 0 ]
        MyData[noparse][[/noparse] 1 ] := INA[noparse][[/noparse] 1 ]
  
DAT
   MyData     byte 0,0

VAR
  long offset1,offset2

PUB Main

    repeat    
      offset1 := MyData[noparse][[/noparse] 0 ]
      offset2 := MyData[noparse][[/noparse] 1 ]
      Printit

DAT
   MyData     byte 0,0

This will not work of course. You should have done what Mike had suggested above! And a lot more...
Mike's suggestion would have lead to the following code; I resort the object tree so it makes sense

VAR
  long offset1,offset2
OBJ A: "PeekAndPokeA"

PUB Main 
    A.start(@MyData)
    repeat    
      offset1 := MyData[noparse][[/noparse]0]
      offset2 := MyData
      Printit

DAT
  MyData     byte 0,0

VAR
   LONG stack[noparse][[/noparse]20]
PUB start(thePointer)
   pointer := thePointer
   COGNEW(Button, @stack)

PUB Button 
   repeat
        BYTE[noparse][[/noparse]pointer][noparse][[/noparse] 0 ] := INA[noparse][[/noparse] 0 ]
        BYTE[noparse][[/noparse]pointer][noparse][[/noparse] 1 ] := INA[noparse][[/noparse] 1 ]

All right?

----
Edit: Oh, Mike was 3 minutes faster Well I am a slow typer...

Post Edited (deSilva) : 1/7/2008 12:12:26 AM GMT

bgw56

Thanks for your answers. I'll let you know how I make out. Could take a while.
BW