Question about shared variables

Laurent R

Hi all

Here is my goal :
- main cog receive command like launch a new cog to do a task in backgound

- this second cog need to know some variables from the main code so I give him as parameters when he starts

First question : is it the right way or not ?

Second : If the second cog changes a variable, will the first cog see this modification?

VAR

  Byte  AnalogDefaultChan
  Byte  DefaultRange
  Byte  DefaultBip
  
  long  ValAlarmHi              
  Byte  High_Pos                 
  long  ValAlarmLo              
  Byte  Low_Pos                 
  Byte  Latch_Alarm            
  byte  Warning_1270_flag

CogAlarm := cognew(alarm.Start(Warning_1270_flag,ValAlarmHi,High_Pos,ValAlarmHLo,Low_Pos,Latch_Alarm),@15)                                       

Thanks for help

Laurent

mpark

First, yes, that's correct.
Second, no, the second cog is operating on its own private copies of the first cog's variables. If you want to transmit information from the second cog to the first, you could pass the address of the variables, like so:
cognew(alarm.Start(@Warning_1270_flag,@ValAlarmHi, etc etc)
but you'd have to modify the Start method accordingly.

SRLM

You may want to poke around this thread. I think there's an answer in there somewhere.

http://forums.parallax.com/showthread.php?p=765086

Mike Green

You can't use a method call to another object in a COGNEW or COGINIT ("alarm.Start"). It's not well documented and the compiler won't catch it, but it won't work.

mpark

D'oh! Missed that. (Homespun can flag those errors, btw, even if I can't.)

Mike Green

I think there are some examples in the Propeller Education Kit tutorials that you can download that show how to pass global variables from one object to another.

The compiler sorts global variables in an object according to their base size. Longs are first, then words, then bytes. If you're going to pass groups of variables of the same base size, you can just pass the address of the first variable and reference the others as if you were passing an array (using BYTE / WORD / LONG like LONG[noparse][[/noparse] variable address ] [noparse][[/noparse] subscript ]). You can also pass the addresses of each of the variables if there are only a few.

Laurent R

Thanks at all

I'll see that

---

edit :

@ Mike : And if cognew is in the other object?

so I call "alarm.start" and the start method open a new cog it's the right way , is'nt it?

Best regards

Laurent

Post Edited (Laurent R) : 4/10/2009 9:01:13 AM GMT