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

[David Brown]

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.