Re: Stream_Element_Array

[Alexander Korolev <antonovkablog@gmail.com>]

On Sep 14, 7:08 pm, "Dmitry A. Kazakov" <mail...@dmitry-kazakov.de>
wrote:
> On Wed, 14 Sep 2011 07:48:47 -0700 (PDT), Alexander Korolev wrote:
> > I am talking to serial port via GNAT.Serial_Communication. The
> > Buffer it offers is Stream_Element_Array.
>
> In that case it is OK to use Stream_Element.
>
> > And I need to do
> > computations (implemented assuming that the buffer is ok :) ) over the
> > buffer
> > before do the call.One of the formats receiving part expects is:
> >|Start(8bit|Length - 16 bit|Element1-8bit|Element-16bit|Checksum|
> > Write (S_Port,Buffer)
>
> I usually allocate an output buffer in the "device object". The output
> index as I described earlier is also stored there. The application level
> fills the buffer and in the end call something like Device.Flush. Flush
> calculates the checksum over 1..Index - 1, stores the result and finally
> calls Write.
>
> BTW, it is highly recommended to use asynchronous read, or a synchronous
> one from an independent task. You should always be ready to read next byte
> from the device. Otherwise you risk to run into a deadlock upon protocol
> errors.
>
> You might also wish to write asynchronously (to improve performance), but
> beware that most serial devices, at least those I saw, are broken and just
> crash when full duplex I/O attempted.
>
> --
> Regards,
> Dmitry A. Kazakovhttp://www.dmitry-kazakov.de
"I usually allocate an output buffer in the "device object"

I've been advised and that worked out for many in few cases to use
Volatile_Streams.Memory_Resident_Stream.
You may like to take a look (in GNAT Examples) if you have not
already did
before. I was getting a compilation error like I posted before (see my
second post)
but now it's gone and I hope I got what I wanted but further autopsy
will show ...
I will post the result if it will work this way.

" or a synchronous one from an independent task"
Sure. This is were I call the serial port