[rtems commit] smpcapture02: Add test of functionality to add custom entries to capture trace

Joel Sherrill joel.sherrill at oarcorp.com
Fri Feb 13 15:15:53 UTC 2015

On 2/13/2015 2:54 AM, Chris Johns wrote:
> On 13/02/2015 7:06 pm, Sebastian Huber wrote:
>> On 13/02/15 08:56, Daniel Cederman wrote:
>>>> Daniel(s), could enlighten me why this is needed ? Is this a arch
>>>> constraint or something else ?
>>>> Chris
>>> It is an arch constraint. On SPARC, for example, all memory accesses
>>> needs to a be aligned. From the SPARC V8 manual:
>>> "Halfword accesses must be aligned on 2-byte boundaries, word accesses
>>> must be aligned on 4-byte boundaries, and doubleword accesses must be
>>> aligned on 8-byte boundaries. An improperly aligned address in a load
>>> or store instruction causes a trap to occur."
>>> Since the capture engine does a 64-bit write when it writes the time,
>>> the entries needs to be aligned on 8-byte boundaries.
>> If you need this hack in the test, then there is a bug in the caputure
>> engine.
> Agreed, and what I was wondering.
> Maybe the capture engine needs a buffer alignment arg so the data 
> transfers match up.
malloc is supposed to return buffers aligned to the strictest requirements
of the architecture. This usually results in 4 or 8 byte alignment. Maybe
the capture engine just needs to follow the same rule.
> Chris
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Joel Sherrill, Ph.D.             Director of Research & Development
joel.sherrill at OARcorp.com        On-Line Applications Research
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