Need help to understand about SPIN ...

Comments

• wjsteele Posts: 697

  2010-08-14 07:11 edited 2010-08-14 07:11

  Is your question about not having to have the @ symbol on your second paramater in the snG.Start method? If so, it is because @ means address. But a string is always handled as an address when you use the "String" method to construct it. (In fact, in reality, it's an address to the physical string of bytes in your code, like a constant.)
  
  When you assign that String to a variable, you're assigning the address to that variable, which you are then passing into your start method. So, if you added the @ to the second parameter, you would instead be sending the address of the address variable (startGInputFile) in memory and not the address of the value ("inputfil.log") in memory.
  
  Bill
• John Abshier Posts: 1,116

  2010-08-14 07:22 edited 2010-08-14 07:22

  > byte startGInputFile[13]
  looks like it is designed to hold a file name 8 for name, period, 3 for extension, 1 for $00
  > startGInputFile := String("inputfil.log")
  String returns the address of where "inputfil.log" is stored. So startGInputFile should be a long to hold an address
  
  John Abshier
• MacTuxLin Posts: 821

  2010-08-14 07:25 edited 2010-08-14 07:25

  Thanks Bill! Got a very clear picture now.
• MacTuxLin Posts: 821

  2010-08-14 07:34 edited 2010-08-14 07:34

  Thanks John. Another light-bulb just lighted up over my head. So, I'm not storing the actual string but the address of the string therefore I should:
  

  VAR
     long startGInputFile, startGOutputFile
  

  
  Sorry, one more question. So does it mean I don't need to care where the actual string is stored in hub RAM? If so, is it better to declare all string variables after other variables?
  

  VAR
     'Using as registers 
     byte servoReg[16]
     byte proximityReg[2]
  
     'Shared memory
     byte memBlockA[512]
  
     'String variables
     long startGInputFile, startGOutputFile
  

  
  Thank you.
• John Abshier Posts: 1,116

  2010-08-14 07:46 edited 2010-08-14 07:46

  The Spin tool reorders the variables, all longs, followed by all words, followed by all bytes. See page 212 of the Spin Manual DAT items are not rearranged. See page 100 of the manual
  
  John Abshier
  
  PS. First 8 global longs are accessed faster than the rest.
• MacTuxLin Posts: 821

  2010-08-14 08:18 edited 2010-08-14 08:18

  Thanks John.
• BradC Posts: 2,601

  2010-08-14 19:26 edited 2010-08-14 19:26

  John Abshier wrote: »

  PS. First 8 global longs are accessed faster than the rest.

  
  As are the first 8 local longs starting from RESULT.
• MacTuxLin Posts: 821

  2010-08-16 01:09 edited 2010-08-16 01:09

  Got it. Thanks Brad.