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From: Niklas Holsti <niklas.holsti@tidorum.invalid>
Newsgroups: comp.lang.ada
Subject: Re: STM32F4 Discovery, communication and libraries
Date: Fri, 29 Aug 2014 00:17:12 +0300
Organization: Tidorum Ltd
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Xref: news.eternal-september.org comp.lang.ada:21970
Date: 2014-08-29T00:17:12+03:00
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On 14-08-28 23:09 , Dmitry A. Kazakov wrote:
> On Thu, 28 Aug 2014 09:28:15 -0700 (PDT), Mike Silva wrote:
> 
>> On Thursday, August 28, 2014 6:00:12 AM UTC-7, Dmitry A. Kazakov wrote:
>>> One of the responsibilities of the OS and the middleware is to perform I/O
>>> on things like ModBus in background without blocking the application and
>>> other I/O. Even a very lame board is usually much faster than any ModBus
>>> terminal.
>>
>> Maybe there is some confusion being caused by the term "OS" here.  Ada's
>> concurrency and realtime functionality can run on top of an OS, but it can
>> also run on bare metal (an "invisible" OS?).
> 
> Not really. OS is more than tasking, it is also a queueing mechanism, which
> allows waiting for I/O completion in one task without blocking all other
> tasks.
> 
>> The GNAT ARM Cortex M
>> release does have Ravenscar tasking on bare metal.
> 
> You could not implement an equivalent of I/O queueing under the Ravenscar
> constraints.

It is certainly possible to implement an I/O request queue in Ravenscar;
I have done so for the platform SW on ESA's GOCE satellite. Multiple
client tasks, one server (interface driver) task. An I/O request
contains (or is, or refers to) a client-specific protected object (PO)
with an "I/O completed" entry, on which the client task waits after
enqueueing the I/O request. The server task processes submitted I/O
requests in any order and concurrency it chooses; when an I/O request is
done, the server task calls an operation on the request's PO, which
unblocks the entry, resuming the client task.

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