Hallo Cédric,
if I understood your problem the workaround could be a compiler directive to
override the
default compiler memory aligment policy, of course this directive is strongly
bound to the
compiler itself but it usually sounds like a 'pragma' directive i.e. #pragma
option push -a1,
#pragma pack(1). Anyway look into compiler manual and you will find this
information easily.
From: Cédric Marzer
Sent: Friday, September 04, 2009 8:47 AM
To: address@hidden
Subject: [Paparazzi-devel] I need an expert in C
Hello,
My OSD makes good progress but I am stuck with some C trick.
The messages are stored in an array each char, short or long following each
other.
I want to map this message into different structures (for the gps message, the
batterie message, etc.).
The crude way to do that (it works), is the following :
gps.utm_north=MAKE32(array[12],array[11],array[10],array[9];
etc.
But that means that I will write a dozen of this for each message.
The (not so smart) way is to do that :
gpspointer=&array+4
but there is a trap.
When you make a structure, the compiler makes sure that the short and long are
aligned in the memory
and add gaps after let's say a char to make sure that the next long is well
aligned in the memory.
That means that the data in my array and in the structure are not aligned. The process to
put the gaps is called "padding".
Some compiler and processor allow one to disable "padding". I doubt that this
is the case with arm.
So does anyone of you have a smart idea for a clean work around ? Otherwise I
will just go the crude way.