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saving struct values in eeprom

 
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soundscu



Joined: 29 Jun 2007
Posts: 62
Location: Raleigh, NC

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saving struct values in eeprom
PostPosted: Tue Aug 07, 2007 1:16 pm     Reply with quote

Hi all. Smile

I need to backup values in a complex struct to/from eeprom. The easiest way, I think, would be to access the individual bytes of the struct like the elements of an array. The struct uses a total of 43 bytes, consisting of various int8s, int32s, and 32-bit floats.

Are the bytes of a struct kept contiguous by the compiler?

Is there an easy way to do this in c?

Thanks for your help and/or suggestions.

Sincerely,
Jim
PCM programmer



Joined: 06 Sep 2003
Posts: 21708

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PostPosted: Tue Aug 07, 2007 4:41 pm     Reply with quote

See this post, regarding a union between an array and other structure
elements.
http://www.ccsinfo.com/forum/viewtopic.php?t=18729

That method depends upon CCS packing all structure elements on a
1-byte boundary, with no padding. I believe they do that.

The reason for the delay in answering was that I kept searching the
archives for an old post, where I state that. I couldn't find it, so I
just finally re-stated it above.
soundscu



Joined: 29 Jun 2007
Posts: 62
Location: Raleigh, NC

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Thanks!
PostPosted: Tue Aug 07, 2007 7:50 pm     Reply with quote

Your suggestion has led to a working routine! The syntax for using a struct in a union isn't quite what I thought it was.

Incidentally, my application is a touch more complicated because I use a 7-element array of the struct I defined. Evenso, success!

Thanks very much.

But now I have a new problem... see my new subject "write_eeprom not working with PIC18F6722". :(
Pret



Joined: 18 Jul 2006
Posts: 92
Location: Iasi, Romania

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PostPosted: Wed Aug 08, 2007 12:21 am     Reply with quote

Personally i have similar question. Is there any way to declare a data structure directly in EEPROM using #rom directive? Something like:
Code:
typedef struct
{
  int8 x;
  int16 y;
  ZaOtherThing t;
  char z;
}ZaThing;
and later on:
Code:
#rom ZaThing 0xF00008 = {4,450,{45, 22}, 'a'};
without declaring byte by byte?
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