[rtems commit] Using the generic atomic ops to implement UP mode atomic for all architectures . SMP atomic port will be later.

[Gedare Bloom]

On Wed, May 1, 2013 at 10:44 AM, Ralf Corsepius
<ralf.corsepius at rtems.org> wrote:
> On 05/01/2013 04:23 PM, Gedare Bloom wrote:
>>
>> Module:    rtems
>> Branch:    master
>> Commit:    9b605b28b497f398682a8ffd673f6860340957f8
>> Changeset:
>> http://git.rtems.org/rtems/commit/?id=9b605b28b497f398682a8ffd673f6860340957f8
>>
>> Author:    WeiY <wei.a.yang at gmail.com>
>> Date:      Wed Apr 24 00:34:16 2013 +0800
>>
>> Using the generic atomic ops to implement UP mode atomic for all
>> architectures. SMP atomic port will be later.
>
>
>> +++ b/cpukit/score/cpu/arm/rtems/score/cpuatomic.h
>> @@ -0,0 +1,40 @@
>> +/**
>> + * @file  rtems/score/cpuatomic.h
>> + *
>> + * This include file implements the atomic operations for arm and defines
>> + * atomic data types which are used by the atomic operations API file.
>> This
>> + * file should use fixed name cpuatomic.h and should be included in
>> atomic
>> + * operations API file atomic.h. If the architecture works at the UP mode
>> it
>> + * will use a generic atomic ops using disable/enable-IRQ simulated. If
>> the
>> + * the architecture works at SMP mode, most of the parts of
>> implementations
>> + * are imported from FreeBSD kernel.
>> + */
>> +
>> +#ifndef _RTEMS_SCORE_ATOMIC_CPU_H
>> +#define _RTEMS_SCORE_ATOMIC_CPU_H
>> +
>> +#include <rtems/score/genericcpuatomic.h>
>> +
>> +#ifdef __cplusplus
>> +extern "C" {
>> +#endif
>> +
>> +/**
>> + * @defgroup RTEMS atomic implementation
>> + *
>> + */
>> +
>> +/**@{*/
>> +
>> +#if !defined(RTEMS_SMP)
>> +#include <rtems/score/genericatomicops.h>
>> +#else
>> +#endif
>> +
>> +#ifdef __cplusplus
>> +}
>> +#endif
>> +
>> +/**@}*/
>> +#endif
>> +/*  end of include file */
>
>
> Would somebody please explain the code above?
>
This file splits the code for the atomic operations into two cases,
uniprocessor and SMP. The uniprocessor (UP) generic framework disables
and enables interrupts around the operation and can be used by any
CPU. In SMP mode, the CPU should define the atomic operations. For the
ARM and many other RTEMS targets, SMP mode is not supported so we do
nothing here. In the future, the #else branch would include the atomic
operations that are available for SMP.

> The #ifdef __cplusplus as well as the #if !defined(RTEMS_SMP)
> should be completely superflous. If not, they'd indicate bugs elsewhere.
>
The C++ guard is commonly used in score headers. I don't think anyone
has codified when it can be removed. It does seem this file does not
need it.

The SMP mode should be left as a placeholder for when SMP support is
added. Perhaps a #warning or even #error should be added there to
indicate there is a problem.

> Ralf
>
>
>
>
>
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