Re: ARM and padding

[Luke Diamand <ldiamand@virata.com>]

Looking at your structure, and noting that the data is not word aligned
in the first place, I suspect you may struggle to get this approach to
work - won't the ARM end up totally garbling the word access to the int
field three quarters of the time?

You might prefer to use direct byte reads and manipulations - e.g.

inline int getRemainingBytes( unsigned char *bytes ) {
    unsigned char *ptr = bytes+251;
    return ptr[0]+(ptr[1]<<8)+(ptr[2]<<16)+(ptr[3]<<24);  // or
something like that
}

This also has the virtue that you can cope better if you get endian
blues.

Just my 2c.


jens.ohlund@secrc.abb.se wrote:
> 
> Hi !
> 
> My problem is the following:
> I have an ARM Evaluation Board-1. Rev B. I receive data from a serial line.
> this data is placed in a linear buffer, and then i typecast to a struct of some kind.
> 
> This data which i receive I cannot control, and have therefore to work with it as is.
> 
> The structs contains other structs and so on and in the end it's only 16 or 8 bits values a extract.
> BUT these values are not aligned, and when I typecast I get the wrong values, since the buffer is "packed".
> 
> How do I tell the compiler that the structs are to be packed ?
> 
> I'm developing on NT4, using cygwin and gcc-2.95.2 (arm-elf-gcc).
> 
> yours
> Jens Ohlund
> 
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