how to force 32-bit access

[Maett]

Hi.

I have an interface card that only allows 32-bit access.
How can I make sure that g++ does not make optimizations that might
end in 8-bit or 16-bit accesses ?

Example:

If I have
  volatile unsigned long *pInterface;
  const unsigned long myflags = 0x40000000;
  *pInterface |= myflags;

g++ might theoretically leave the 3 low bytes of *pInterface untouched
and only make an 8-bit access to byte # 4.

What can I do to be *sure* it doesn't ?

Maett