On 2012-10-23, Theodore Ts'o <tytso@xxxxxxx> wrote:
> On Tue, Oct 23, 2012 at 06:45:51PM +0000, Grant Edwards wrote:
>> FWIW, in some products we're planning that will require support for
>> various industrial serial protocols, I'm leaning towards abandoning
>> the tty driver approach and writing a stand-alone character device
>> driver. The byte-stream oriented tty/line-discipline layer just
>> doesn't fit well when dealing with frame-oriented industrial protocols
>> that depend on things like 9th bit addressing and detecting
>> sub-millisecond inter-byte timeouts.
>
> You might want to take a look at how the ppp line discipline (which
> is obviously highly packet oriented) works. One advantage of doing
> things that way is if you have a multiport serial card, where some
> ports want to play this packet-oriented approach, and other cards
> might be connected to a traditional modem or terminal sort of device,
> you won't have to figure out how to share a PCI board between two
> different drivers, allocating one port to the traditional tty/serial
> driver, and another one to your new driver, etc.
Thanks for the suggestion. I did look into line-disciplines briefly
quite a while back. Most of the information I found implied that
adding a line disciplilne wasn't something you could do at run-time by
loading a user-built module -- it would require recompiling parts of
the kernel. Articles made statements about having to modify kernel
include files like tty.h. If that's wrong, then a line discipline
might be a good option.
--
Grant Edwards grant.b.edwards Yow! I'm having a
at quadrophonic sensation
gmail.com of two winos alone in a
steel mill!
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