Re: Help with embedded hardware/software platform selection for ADA

["Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>]

On Tue, 2 Jul 2013 16:52:59 +0000 (UTC), Simon Clubley wrote:

> On 2013-07-02, Dmitry A. Kazakov <mailbox@dmitry-kazakov.de> wrote:
>> On Tue, 02 Jul 2013 09:27:40 +0200, Georg Bauhaus wrote:
>>> 
>>> I still wonder why not a single vendor sells a Ravenscar run-time
>>> with compiler at a hobbyist price, without support.
>>
>> Why a hobbyist would even look at Ravenscar?
>>
>> IMO, a hobbyist if not obsessed with systems programming, wants full Ada
>> and a "normal" OS. This is quite possible to have today. And this is where
>> Ada shines, because you can develop and test on a PC and then just
>> recompile the code for the embedded target without any changes. At least
>> this is the way we do it.
> 
> It's not just systems programming, but hard realtime programming.
> 
> If you are using a "normal" OS, can I assume you don't have a hard
> real-time requirement (at least within the Ada code itself) ?

Hard realtime is to a great extent a fiction. If your system becomes
fragile upon us jitter there should be something wrong with the
architecture.

Otherwise there is no problem to have a 100us control loop under a "normal"
OS like Linux or VxWorks. Even under Windows you can have stable 5ms
(Windows has timer resolution issues, performance is basically OK).

We do some control under normal Windows using I/O terminals connected
through normal networks, e.g. ModBus over TCP/IP. Of course, we could not
certify such a system, but we don't care. A hobbyist would care even less.

> A number of the project areas which interest hobbyists have a realtime
> component to them and a number of those have a hard realtime component.

Unless you are dealing with burning processes (a bomb? (:-)) you do not
need cycles tighter than 1ms. And jitter is not an issue anyway.
Furthermore, a good AD/DA converter is not quicker than 40us. Which adds
80us to the loop no matter what. Don't tell me that the GPIO ARM has is
anywhere close to this. So 100us would be the theoretical minimum.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de