Re: [avr-gcc-list] Re: External EEPROM verses internal EEPROM data handling

[Daniel O'Connor]

On Mon, 4 May 2009, David Brown wrote:
> Daniel O'Connor wrote:
> > On Mon, 4 May 2009, Bob Paddock wrote:
> >>>                uint16_t voltage[24];   // adc counts of 24
> >>> channels in an array } ED;           // total data = 58 bytes
> >>
> >> Because of issues of structure packing it is better to define
> >> structure items from
> >> the largest to the smallest, ie. uint16_t should be first.  This
> >> is more important
> >> on 32bit processors and up than on the 8bit AVRs.
> >
> > You could just mark the struct as packed, eg..
> > typedef struct eventdata {
> >  ...
> > } __attribute__ ((packed)) ED;
>
> Or use the -wpadded warning flag, which will let you know if any
> implicit padding has been added (I prefer to explicitly add padding
> if it is required).
>
> Of course, you don't get padding on an 8-bit AVR (except for bit
> fields), but it's good to write portable code when practical.

Padding is going to be unportable between architectures.. May as well 
take advantage of the compiler extensions. (IMO :) 

-- 
Daniel O'Connor software and network engineer
for Genesis Software - http://www.gsoft.com.au
"The nice thing about standards is that there
are so many of them to choose from."
  -- Andrew Tanenbaum
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