Re: STM32F4 Discovery, communication and libraries

[Niklas Holsti <niklas.holsti@tidorum.invalid>]

On 14-09-01 19:42 , Dmitry A. Kazakov wrote:
> On Sun, 31 Aug 2014 21:41:15 +0300, Niklas Holsti wrote:
> 
>> On 14-08-31 10:02 , Dmitry A. Kazakov wrote:
> 
>>> No_Local_Protected_Objects means all requests are pre-allocated at the
>>> library level and distributed by another protected object? With busy
>>> waiting for a free request?
>>
>> No, the _request_ in my example code is not a protected object; it is an
>> ordinary record type. It _refers_ to a protected object which is a kind
>> of "I/O wait object".
> 
> That was clear.

Good, but in that case your comment, quoted above, was rather
misleading, because it clerly implies that requests are affected by
No_Local_Protected_Object.

>> For publish/subscribe, I would do something like this (not tested):
> [...] 
> 
> You don't need anything this complex so long you monitor a single channel.
> The challenge is to subscribe to several channels and also to avoid
> unnecessary copying of I/O data.

So, explain how you do it with the full Ada tasking profile, and I'll
see if I can implement the same thing under Ravenscar rules. Or show a
simpler solution for one channel under Ravenscar rules, that would also
be interesting.

I/O data copying can be avoided by passing references and using
reference counting. I don't see any particular drawback of Ravenscar
rules here -- one either copies data from one task to another, or refers
to shared data, which then needs some sort of cross-task life-time
management.

> Theoretically you could create channels
> that are combinations of queues of events to monitor register them by the
> queues. I don't know how much overhead it will be (I was trying to reduce
> number of protected actions per event), but it looks ugly and overly
> complicated.

General rule: a simpler, less powerful language (Ravenscar) leads to
more complex application programs, when the application functionality is
kept constant. You pays your money and you takes your choice.

-- 
Niklas Holsti
Tidorum Ltd
niklas holsti tidorum fi
      .      @       .