Re: Reading accurate size of recepts from serial port

[Richard B. Johnson]

On Wed, 27 Aug 2003, Laurent [iso-8859-1] Hugé wrote:

> Le Mercredi 27 Août 2003 16:50, Herbert Pötzl a écrit :
> > hmm, why not do simple framing ...
> > [length]<data>[length]<data> ....
> That's impossible. CCSDS is the committee for space date systems and it
> provides standards that I can't overrule (even if I can't really understand
> why they've done it like that !).
> --
> Laurent Hugé.
>

The transfer frame in your reference specified, contains all
the information necessary for the protocol, even if it's stupid
to use that protocol on a RS-232C link. Nevertheless, there is
a minimim size for the header (5 octets in length). There is
also the 3 octets used for sync, which I'm pretty sure will
not be put onto the RS-232C links. Anyway, you need to read
40 bytes (always), from that, you will learn the length
of the rest of the data. So you use poll()/read() until you
get that header information. Then you will know what the
total read-length should be.

Cheers,
Dick Johnson
Penguin : Linux version 2.4.22 on an i686 machine (794.73 BogoMips).
            Note 96.31% of all statistics are fiction.


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