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Date: Fri, 26 Apr 2013 08:27:39 -0700 (PDT)
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Subject: Synchronization: delays x hardware timers
From: "Rego, P." <pvrego@gmail.com>
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Date: 2013-04-26T08:27:39-07:00
List-Id: <comp.lang.ada>

Dear friends,

I would very appreciate your opinions about synchronization. I have a globa=
l (static) variable which is send periodically over the communication media=
 and a flag is checked each cycle to get the equipment response about that =
sent message. In this case, two different flags must be sent in order to ha=
ve the correct response.

So I have an asynchronous call to a procedure Request_Action:

Global_Flag :=3D Flag_Type; -- This is sent periodically.
procedure Request_Action is
   Initial_Response : Response_Type :=3D Get_Response; -- which is /=3D NUL=
L_RESPONSE
   Updated_Response : Response_Type :=3D NULL_RESPONSE; -- NULL_RESPONSE is=
 constant
  =20
   while Updated_Response < Initial_Response loop
      Global_Flag :=3D FIRST_FLAG; -- Now I should wait for the response to=
 be ready
      <Process_Wait>;
      Global_Flag :=3D SECOND_FLAG; -- Now I should wait again.
      <Process_Wait>;

      Updated_Response :=3D Get_Response;
   end loop;
end Request_Action;

The question is which is the best way to implement the <Process_Wait>. The =
application is soft real-time and I just need to ensure that Global_Flag to=
 be processed before the next cycle begins. Also, I need to use only Ada 95=
.

I think that if I use a simple delay it's very enough; and since I do not h=
ave a hard real-time deadline, I even do not need to use delay until. A col=
eague argued with me saying that I must use hardware timers any case. Perso=
nally I think it's an unnecessary use of hardware resources.

I would simply code this as=20
   delay CYCLE_TASK + CYCLE_DELTA;

Thus, what is your opinion?

Thanks very much.