[ILUG] Re: Serial port

[Frank Duignan]

Silly me - 0xff is not a BREAK however the trick still stands and has
saved my bacon in the past.

On 4/4/06, Brian Foster <blf at blf.utvinternet.ie> wrote:
>   | Date: Tue, 4 Apr 2006 21:11:40 +0100
>   | From: "Frank Duignan" <frank.duignan at gmail.com>
>   |
>   | I've generally found sending a break character (0xff) is good at sorting
>   | out this sort of first byte synchronization issue i.e transmit 0xff
> before
>   | sending your real data.  The other end should dump the break if its uart
>   | is worth its salt
>
>  NO.  _if_ the peer's UART is "worth its salt",
>  it will not be confused by a (series of) 0xFF
>  or 0x00 octets, as that is not a true BREAK.
>  IIRC, a true BREAK is all lines clamped low for
>  at least ¼ second.  that should not be confused
>  with a valid octet by any UART "worth its salt",
>
>  nowadays, to send a true BREAK, use tcsendbreak(3).
>
>  _however_, I do agree that some(/many?) UARTs are
>  fooled by this trick (and I have used it myself).
>
>  I suspect Pádraig's earlier guess, that CLOCAL is
>  not set, is perhaps more relevant?
>
>  then there's the problem of what really happens if
>  the peer decides there is an incoming BREAK.  some,
>  such as Solaris (viz a very recent thread), throw the
>  system into the boot monitor, which is sometimes a
>  disaster.  others, as Frank suggest, more-or-less
>  resynch, which is perhaps what is wanted/needed here.
>  (there are other possibilities.)   but it is worth a
>  try, albeit it does not "work" will all equipment at
>  all times.
>
> cheers (hoping I haven't made too many mistakes,
> as I just had a very nice French dinner with, of
> course, a very nice French vin!....),
> 	-bl(*hic*)f-
> --
> Experienced (20+ yrs) kernel/software Eng: | Brian Foster   Montpellier,
>  • Unix, embedded, &tc;  • Linux;  • doc;  | blf at utvinternet.ie   FRANCE
>  • IDL, automated testing, process, &tc.   |  Stop E$$o (ExxonMobile)!
> Résumé (CV) http://www.blf.utvinternet.ie  |     http://www.stopesso.com
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