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Re: xAP and embedded devices


  • To: ukha_d@xxxxxxx
  • Subject: Re: xAP and embedded devices
  • From: "PatrickLidstone" <patrickl@xxxxxxx>
  • Date: Thu, 15 Aug 2002 15:24:23 -0000
  • Mailing-list: list ukha_d@xxxxxxx; contact ukha_d-owner@xxxxxxx
  • Reply-to: ukha_d@xxxxxxx

--- In ukha_d@y..., ian.bird@c... wrote:
> Hi guys
>
> I am getting a little concerned that you are all going PC centric
again and
> forgetting the rather meagre abilities of embedded devices.
>
> It has taken me at least a year to get where I am with my IR
project.
> However, I was starting from scratch and the program is currently
running at
> 1400 code lines (not comments) of assembler. I think it is time to
review
> the target devices again. I don't have the time (or funds) to learn
how to
> program another PIC micro let alone another breed like Rabbit, AVR
etc.
> Ideally I will be using PIC 16F628 chips with 2k program and about
150 bytes
> of spare RAM. Using SNAP a packet has about 7 bytes of overhead
including 16
> bit CRC which I don't have to store as I can process them as they
come in.
> The message data I do have to store and rapidly fills my available
RAM. My
> RS485 network works at 19200 and I think these displays run at 9600
max so
> some storage is essential. Please bear this in mind. The cost of
this chip
> is around 2 to 3 quid, one of its good points.

So should we go back to the original version of the protocol, which
requires less overhead to process, then? Sensible use of separators
(say xAP.source=ABC) could provide equivalent hierarchy to the curly
brace notation. Use of sensible abbreviations could also reduce
storage requirements (e.g. xAP.src). I'd be reluctant to adopt an op-
code dictionary (e.g. Message key represented by byte sequence
<0x00><0x01> is xAP.source) because of the problems of maintaining
the dictionary in the long term.

Another feature which can help with on-the-fly processing is
insisting on tag order. Whilst certain name-value pairs may not be
mandatory, specifying an order may help with state driven parsing?

Patrick


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