Volatile and Registers

[Mike Halloran]

Normally, when I write software to access a register, I will do
something like this:
*((volatile u32*) 0x00000022) = 5; (with some wrappers to make it
cleaner)

however, I noticed that in a recent codebase that my company aquired,
volatile
is not used:
*((u32*) 0x00000022) = 5;

Is this a proper way of coding? I was under the understanding that if
volatile is not used, the code could be optimized out. Is this
correct? What does
everyone else do?

[Richard Bos]

Re: Volatile and Registers

Eric Sosman <esosman@ieee-dot-org.invalidwrot e:

Mike Halloran wrote:

Normally, when I write software to access a register, I will do
something like this:
*((volatile u32*) 0x00000022) = 5; (with some wrappers to make it
cleaner)

>
First, I hope you realize that converting integers to
and from pointers is inherently "unclean," and relies on
characteristics of the particular system you happen to be
using. It's a common technique for getting at things like
hardware registers, but it's not a portable technique.

Actually, the technique itself is portable. The numbers are not. I would
not expect any given system to let you write to any given address, but
if some system does allow you to write directly to some addresses, this
is precisely the technique I would expect to be able to use.

Richard