Re: Ravenscar - release multiple tasks when an event occurs

[Simon Wright <simon@pushface.org>]

Jere <jhb.chat@gmail.com> writes:

> On Sunday, May 3, 2020 at 6:43:31 AM UTC-4, Simon Wright wrote:
>> I have several sensor tasks (in general, 2 at the moment) which will of
>> course be created and start execution during elaboration.
>> 
>> I'd like to ensure that they don't actually start reading and reporting
>> input data until the system is in a state to receive them.
>> 
>> With the Ravenscar profile it's not obvious how to do this (only one
>> entry per PO, only one task allowed to queue). I suppose I could just
>> ignore the inputs until the system's ready to receive them! but has
>> anyone a scheme which is less clunky?
>> 
>> An alternative would be to try for the Jorvik profile, which does allow
>> multiple tasks to queue on one entry.
>
> I don't have any experience using ravenscar, so this is somewhat of 
> a question as well as a potential option.  I know you cannot do
> relative delays, but can you do absolute delays?  If so, could that 
> then give you the option to have a single protected object with a
> get function and set procedure (no entries) and you just spin lock
> at the beginning of all your tasks looking for that protected 
> object to change state? 

With Ravenscar, you can _only_ do absolute delays. Jorvik (not yet in
the compiler, GNAT_Extended_Ravenscar is the equivalent) allows relative
delays too.

I think it would be unwise to spin lock! A loop with a short delay would
do.