volatile in struct

Eric Norum norume at aps.anl.gov
Wed Feb 18 13:07:25 UTC 2004

On Feb 18, 2004, at 2:50 AM, Sergei Organov wrote:

> Juergen Zeller <juergen.zeller at argovision.de> writes:
>> Thank you for all your statements. But this is not the key for my 
>> question.
>> Unfortunately somebody cut out my first mail, so I'm not wondering 
>> something
>> 'other' is discussed. Here my first questiion again:
> It has been answered already. Here is the initial answer:
> 1. You should protect your shared data with *the same* primitive in 
> all the
>    threads. Either use rtems_interrupt_x in both threads or use
>    rtems_semaphore_x in both threads.
> 2. Using volatile is almost never a good idea. If you use RTOS 
> primitives for
>    mutual exclusion correctly, you don't need volatile for your 
> protected
>    data.

All-encompassing statements like 'almost a never a good idea' are 
likely to confuse the novice.  Yes, using volatile variables is 
probably not a good way to share data among tasks.  But volatile is 
absolutely necessary when working with 'variables' that are actually 
I/O registers.
Eric Norum <norume at aps.anl.gov>
Advanced Photon Source
Argonne National Laboratory
(630) 252-4793

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