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From: Martin on 10 Feb 2010 03:40 On Feb 10, 8:29 am, Hibou57 (Yannick Duchêne) <yannick_duch...(a)yahoo.fr> wrote: > On 10 fév, 09:17, Maciej Sobczak <see.my.homep...(a)gmail.com> wrote:> > There are two kinds of blockings: bounded and unbounded. The idea is > > > that when computing a time budget, you can account for bounded > > > blockings, but not unbounded ones. > > > The "potentially blocking" phrase should be understood as really meaning > > > unbounded. > > > Well, I know what you try to convey, but there are traps: > > > delay Some_Static_Constant; > > > Is it bounded or unbounded? > > > As far as WCET (or any other time-based analysis) goes, the above can > > be accounted for statically. Still, it is a no-no within any protected > > operation. > > Interesting enigma > > I would say Bounded, as it is predictable. > ... as long as the delay is short, otherwise it will break the other > rule stating that a protected operation should be fast to execute. > > If I try to have a delay X.Y in a protected operation, GNAT just warns > me potentially blocking operation in protected operation , while > the program is still compiled. > > You've said it is a no-no within any protected : do you get a > compilation error when you do the same ? > > I've not seen anything in the Rationale nor in the ARM which > explicitly disallow it anyway (but as these are long pages I should > later read again, I may have miss it). It's isn't predicatable - it will delay for /at least/ Some_Static_Constant. It's up to the task scheduling algorithm (plus the rest of the program! ;-) as to what happen next...and when! Cheers -- Martin
From: Jean-Pierre Rosen on 10 Feb 2010 06:38 Maciej Sobczak a �crit : > On 9 Lut, 15:26, Jean-Pierre Rosen <ro...(a)adalog.fr> wrote: > >> There are two kinds of blockings: bounded and unbounded. The idea is >> that when computing a time budget, you can account for bounded >> blockings, but not unbounded ones. > >> The "potentially blocking" phrase should be understood as really meaning >> unbounded. > > Well, I know what you try to convey, but there are traps: > > delay Some_Static_Constant; > > Is it bounded or unbounded? > For the rules of potentially blocking operations, delay is potentially blocking because it /can/ be unbounded. Many unbounded things can be proved bounded with sufficient analysis and provided some elements are static; that's not the point here. -- --------------------------------------------------------- J-P. Rosen (rosen(a)adalog.fr) Visit Adalog's web site at http://www.adalog.fr
From: Jean-Pierre Rosen on 10 Feb 2010 06:44 Martin a �crit : > It's isn't predicatable - it will delay for /at least/ > Some_Static_Constant. It's up to the task scheduling algorithm (plus > the rest of the program! ;-) as to what happen next...and when! > If your compiler supports annex D, the possible extra delay time has to be documented - see D.9. -- --------------------------------------------------------- J-P. Rosen (rosen(a)adalog.fr) Visit Adalog's web site at http://www.adalog.fr
From: Martin on 10 Feb 2010 07:51 On Feb 10, 11:44 am, Jean-Pierre Rosen <ro...(a)adalog.fr> wrote: > Martin a écrit : > > > It's isn't predicatable - it will delay for /at least/ > > Some_Static_Constant. It's up to the task scheduling algorithm (plus > > the rest of the program! ;-) as to what happen next...and when! > > If your compiler supports annex D, the possible extra delay time has to > be documented - see D.9. > > -- > --------------------------------------------------------- > J-P. Rosen (ro...(a)adalog.fr) > Visit Adalog's web site athttp://www.adalog.fr D.9 (12) in this case? I guess if you're that interested then you do need an Annex D conforming compiler...just looking and yup, GNAT GLP 2009 for WinXP doesn't list that - so non-deterministic for this OS. Cheers -- Martin
From: Robert A Duff on 10 Feb 2010 11:17
Martin <martin.dowie(a)btopenworld.com> writes: > It's isn't predicatable - it will delay for /at least/ > Some_Static_Constant. Well, implementations are supposed to wake the task up as soon as possible after the delay expires. We don't really have a way to say that in RM terms, but an implementation that delays for an extra second, for example, should probably be considered broken. >..It's up to the task scheduling algorithm (plus > the rest of the program! ;-) as to what happen next...and when! Yeah, the rest of the program is key. But that's the case even without delays. For example, suppose a protected procedure says, "X := X + 1;". Looks pretty bounded. But it can get preempted by a higher priority task, which can go off and do stuff for a long and unbounded time. You have to take care to get your priorities right. - Bob |