Re: serial.c (half duplex support)

David Woodhouse (David.Woodhouse@mvhi.com)
Tue, 26 Oct 1999 19:16:04 +0100


tytso@MIT.EDU said:
> At what baud rates does Profibus run? The problem is that you will
> need to read a high-resolution clock at every interrupt, and this is
> (a) slow or unavailable on some architectures, and (b) non-portable.

9600/19200/93750/187500/500000/1500000 baud, of which IIRC only the first two
are possible with the standard clocks and divisors that I'll find on a PC.

get_cycles() is a reasonable abstraction which can be used across a few
platforms (Alpha/MIPS/i586+/sparc64/ppc)

> Some intelligent serial ports will simply not support this at all.

Then it may not be able to get certification while running on those - it
should still be possible to get it to work, though.

I suppose if I don't actually want to get it certified, then I can get it to
work without the timing info - I can definitely manage to send packets OK, it's
just that my interpretation of the spec I quoted earlier is that I _must_ drop
packets which don't quite meet the timing requirements.

Hopefully, the test procedures won't actually involve sending such packets and
making sure that the implementation being tested drops the offending packets.

---- ---- ----
David Woodhouse David.Woodhouse@mvhi.com Office: (+44) 1223 810302
Project Leader, Process Information Systems Mobile: (+44) 7976 658355
Axiom (Cambridge) Ltd., Swaffham Bulbeck, Cambridge, CB5 0NA, UK.
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