Re: Suggested patch for linux

[Grant Edwards <grante@visi.com>]

On 2008-07-18, Laurent Pinchart <laurentp@cse-semaphore.com> wrote:

>> I believe that he is referring to something much simpler than
>> you are thinking.  He is talking about 2-wire RS485
>> transmissions in which the RTS signal is used to enable the
>> driver chips just before transmitting data and disabling
>> (tri-stating) them just after transmitting data.  There are
>> some UARTs that have this behavior built into them.
>
> And that feature is currently not supported by Linux, even
> with UARTs that have hardware support for "Auto RS485" mode,
> such as the 8250-compatible XR16C2850.
>
> The issue is that no flag is defined for the c_cflag field of
> the termios structure to enable that feature. The following
> patch is an example of what would be required.

I'd definitely be in favor of such a flag. It sucks having to
resort to various hacks to control support of that feature in
Linux serial drivers.

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