How can I determine where data is located in EEPROM

Comments

• Luis Digital Posts: 371

  2007-01-12 21:55 edited 2007-01-12 21:55

  A solution can be to write a constant one and then to see where is (with the eyes ), and then to note the direction.
  
  DAT
  Reserved_9_Bytes Byte "RESERVED9"
• Paul Baker Posts: 6,351

  2007-01-12 23:19 edited 2007-01-12 23:19

  For this, you need to use @@ instead of @ to generate the address, @ only provides the relative offeset of the variable wrt the object. @@ provides the absolute address.
  
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  Paul Baker
  Propeller Applications Engineer
  
  Parallax, Inc.
• Bean Posts: 8,129

  2007-01-13 00:47 edited 2007-01-13 00:47

  Thanks Paul, I will try that.
  
  Bean.
  
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• cgracey Posts: 14,133

  2007-01-13 04:48 edited 2007-01-13 04:48

  Actually, @variable will return the absolute RAM address which is the same as the EEPROM address. @@ is used to add the current object's base address to some offset value so that you will then have an absolute address:
  ·
  PRI StringAddress(Efficient, StringNum)
  ·
  · if Efficient
  ····return @@strings[noparse][[/noparse]StringNum]··· 'Get the absolute address of string1, string2, or string3
  · else
  ····return lookupz(StringNum : @string1, @string2, @string3)··· 'Do the same thing less efficiently
  ·
  ·
  DAT
  ·
  strings·· word·· @string1, @string2, @string3
  ·
  string1·· byte·· "Ay",0
  string2·· byte·· "Bee",0
  string3·· byte·· "Sea",0
  
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  Chip Gracey
  Parallax, Inc.
• Remy Blank Posts: 42

  2007-01-13 10:03 edited 2007-01-13 10:03

  Chip Gracey (Parallax) said...
  
  DAT
  
  strings word @string1, @string2, @string3
  
  string1 byte "Ay",0
  string2 byte "Bee",0
  string3 byte "Sea",0
  

  
  Now I'm confused. Does this mean the "strings" line above stores three offsets relative to the current object's base address? How can I then store three absolute addresses? With @@string1?
  
  -- Remy
• cgracey Posts: 14,133

  2007-01-13 11:25 edited 2007-01-13 11:25

  Remy Blank said...
  
  Now I'm confused. Does this mean the "strings" line above stores three offsets relative to the current object's base address?
  
  Yes. While, @label is usually used in Spin, @label can be used within DAT/word declarations to store offsets of DAT variables within the object.
  
  How can I then store three absolute addresses? With @@string1?
  
  
  @@ is only usable at run-time in Spin. For example, @@0 will return the base address of the object. Because objects are entities unto themselves and relocatable during compilation/mixing, they don't know their absolute address at compile-time. It can only be learned at run-time. While it is possible to make the compiler patch addresses, it would complicate its internals greatly. During development of the Spin language, the door to live setup/takedown of objects was left open through some potential operating system, requiring that objects work wherever they are placed, but now, in practice, objects do have stable addresses, they just aren't known at compile time.
  
  -- Remy

  O
  
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  Chip Gracey
  Parallax, Inc.
• Remy Blank Posts: 42

  2007-01-13 13:45 edited 2007-01-13 13:45

  Thanks Chip, now I understand.
  
  Is that why data addressed by RDLONG/WRLONG and friends is always defined in the VAR section, even if it is only used by assembly code? Because in that case, the @ operator returns an absolute address? But that would mean that the address of VAR sections is known at compile-time?
  
  Anyway, the current implementation in my assembler is buggy
  
  -- Remy