Re: Do you use serialization formats for communication?

From	Chris <xxx.syseng.yyy@gfsys.co.uk>
Newsgroups	comp.arch.embedded
Subject	Re: Do you use serialization formats for communication?
Date	2016-11-06 14:49 +0000
Organization	Aioe.org NNTP Server
Message-ID	<nvnfue$1f1l$1@gioia.aioe.org> (permalink)
References	<nu8rm7$4ka$1@dont-email.me>

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On 10/19/16 22:22, pozz wrote:
> I often have the need to exchange some data between two or more MCUs. I
> usually use I2C or UART as physical layers.
>
> Normally I design a simple protocol between the MCUs: one framing
> mechanism (Start Of Frame, End Of Frame), one integrity check mechanism
> (CRC), and so on.
>
> The payload is statically defined between the two MCUs:
> - first byte is the version
> - second byte is the voltage monitoring level
> - third and fourt bytes are some flags
> - ... and so on
>
> As you can understand, both MCUs *must* know and agree about that
> protocol format. However during the lifetime of the product, I need to
> add some functionality or fix some bugs and those activites can lead to
> a review of the protocol format (maybe i need two bytes for the voltage
> level). Sometime, the two MCUs have a different version with a different
> protocol format implementation. In order to avoid protocol
> incompatibility, they all knows about the protocol formats used before,
> so they can adapt the parsing function to the real current protocol format.
> As you can understand, it could be a trouble.
>
> So I'm thinking to use a "self-descriptive" serializer protocol format,
> such as Protobuf, Message Pack, BSON and so on.
>
> Do you use one serialization format? Which one?
>
> Of course, it should be simple to implement (in transmission/encoding
> and reception/decoding) in a small embedded MCU in C language, without
> dynamic memory support.

I'm not sure you need a complex format here, if you think of the
problem in two layers, keeping the protocol layer transparent to data.

A simple frame format could be:

Start of frame byte
Data length, N
Data, N bytes
Checksum or crc
End frame byte

You then write a simple state machine to verify checksum, extract
the data and its length. Pass that to the protocol layer, which
knows where to where to look in the data for it's revision level.
To maintain compatability, any new parameters are tagged on to the
end of the existing data and the data length increased to suit.

Either that, or negotiation between ends to agree capabilities, but
that's much more complex and you should be able to avoid it...

Regards,

Chris

Thread

Do you use serialization formats for communication? pozz <pozzugno@gmail.com> - 2016-10-20 00:22 +0200
  Re: Do you use serialization formats for communication? Dimiter_Popoff <dp@tgi-sci.com> - 2016-10-20 01:30 +0300
    Re: Do you use serialization formats for communication? Simon Clubley <clubley@remove_me.eisner.decus.org-Earth.UFP> - 2016-10-19 23:23 +0000
  Re: Do you use serialization formats for communication? Don Y <blockedofcourse@foo.invalid> - 2016-10-19 16:35 -0700
  Re: Do you use serialization formats for communication? David Brown <david.brown@hesbynett.no> - 2016-10-20 09:40 +0200
    Re: Do you use serialization formats for communication? pozz <pozzugno@gmail.com> - 2016-10-20 13:52 +0200
      Re: Do you use serialization formats for communication? Tauno Voipio <tauno.voipio@notused.fi.invalid> - 2016-10-20 15:58 +0300
      Re: Do you use serialization formats for communication? David Brown <david.brown@hesbynett.no> - 2016-10-20 15:45 +0200
        Re: Do you use serialization formats for communication? pozz <pozzugno@gmail.com> - 2016-10-20 18:06 +0200
          Re: Do you use serialization formats for communication? David Brown <david.brown@hesbynett.no> - 2016-10-20 23:39 +0200
            Re: Do you use serialization formats for communication? George Neuner <gneuner2@comcast.net> - 2016-10-20 21:01 -0400
              Re: Do you use serialization formats for communication? David Brown <david.brown@hesbynett.no> - 2016-10-21 08:56 +0200
                Re: Do you use serialization formats for communication? George Neuner <gneuner2@comcast.net> - 2016-10-23 07:05 -0400
                Re: Do you use serialization formats for communication? David Brown <david.brown@hesbynett.no> - 2016-10-23 18:23 +0200
            Re: Do you use serialization formats for communication? pozz <pozzugno@gmail.com> - 2016-10-21 13:04 +0200
            Re: Do you use serialization formats for communication? pozz <pozzugno@gmail.com> - 2016-10-23 16:07 +0200
              Re: Do you use serialization formats for communication? David Brown <david.brown@hesbynett.no> - 2016-10-23 18:33 +0200
    Re: Do you use serialization formats for communication? kalvin.news@gmail.com - 2016-11-02 02:14 -0700
      Re: Do you use serialization formats for communication? David Brown <david.brown@hesbynett.no> - 2016-11-02 11:17 +0100
  Re: Do you use serialization formats for communication? kalvin.news@gmail.com - 2016-10-20 03:30 -0700
    Re: Do you use serialization formats for communication? pozz <pozzugno@gmail.com> - 2016-10-20 23:18 +0200
  Re: Do you use serialization formats for communication? Chris <xxx.syseng.yyy@gfsys.co.uk> - 2016-11-06 14:49 +0000
    Re: Do you use serialization formats for communication? Chris <xxx.syseng.yyy@gfsys.co.uk> - 2016-11-06 14:58 +0000
  Re: Do you use serialization formats for communication? Vincent vB <embedded@spam.com> - 2016-11-11 09:37 +0100
    Re: Do you use serialization formats for communication? Chris <xxx.syseng.yyy@gfsys.co.uk> - 2016-11-11 12:25 +0000
      Re: Do you use serialization formats for communication? Tim Wescott <seemywebsite@myfooter.really> - 2016-11-11 13:14 -0600
        Re: Do you use serialization formats for communication? Chris <xxx.syseng.yyy@gfsys.co.uk> - 2016-11-11 22:00 +0000
          Re: Do you use serialization formats for communication? Tim Wescott <seemywebsite@myfooter.really> - 2016-11-11 17:51 -0600
            Re: Do you use serialization formats for communication? Tom Gardner <spamjunk@blueyonder.co.uk> - 2016-11-12 00:07 +0000
      Re: Do you use serialization formats for communication? Vincent vB <embedded@spam.com> - 2016-11-29 15:54 +0100

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