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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Subject: Re: Ada.Execution_Time
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Date: Fri, 31 Dec 2010 10:09:27 +0100
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On Thu, 30 Dec 2010 19:40:08 -0500, BrianG wrote:

> Dmitry A. Kazakov wrote:
>> On Tue, 28 Dec 2010 14:14:57 +0000, Simon Wright wrote:
>> 
>>> "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> writes:
>>>
>>>> And conversely, the catastrophic accuracy of the VxWorks real-time
>>>> clock service does not hinder its usability for real-time application.
>>> Catastrophic?
>> 
>> Yes, this thing. In our case it was Pentium VxWorks 6.x. (The PPC we used
>> prior to it had poor performance) The problem was that Ada.Real_Time.Clock
>> had the accuracy of the clock interrupts, i.e. 1ms, which is by all
>> accounts catastrophic for a 1.7GHz processor. You can switch some tasks
>> forth and back between two clock changes.  
> 
> So, we're talking about GNAT's use of VxWorks' features as
> "catastrophic"?  That's not how I read the original statement.

No, GNAT just uses the standard OS clock. It is the OS design flaw. They
should have used the CPU's real time clock, or provide a configurable
clock, so that you could choose its source. Why should AdaCore clean up
Wind River's mess?

Happy New Year,

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de