server: Add support for pending write flag to the serial device. Take 2.

[Dmitry Timoshkov]

Wolfgang Walter <wine at stwm.de> wrote:

> > > I have no intention to discuss that all again. Please think about the
> > > problem. Hint: writing twice as many bytes with 150 baud needs more time,
> > > significantly more time then TIMEOUT.
> > 
> > Not really. Francois sent an investigation with pretty exhaustive
> > explanation of the behvaiour of COM-port UARTs regarding timings and baud
> > rates.
> 
> Have you read it? It says that with a standard UART windows may signals after 
> 872ms that the tx queue is empty (though there are still 4 bytes to send) when 
> you write 17 bytes. For 34 bytes he gets 1802ms > TIMEOUT.

Where do you see 34 bytes to be written in that test?

> And I really don't think that we can expect exactly that same behaviour when 
> using the linux serial driver, anyway.

At the time I was reworking the EV_TXEMPTY to use overlapped IO the reasoning
for using 900 ms as the designed time was simple: that was enough to make the
test pass under Windows with real hardware. How the patch we are discussing
makes the test pass for me under Linux with a USB-serial adapter, which confirms
that there is no reasons that it can't work under Linux as well.

I understand that there are cases of (really old) hardware where this limit
may not be enough, and Francois has already sent a patch which increases
timeout. The Francois' patch hasn't been accepted, but that's a different
matter.

-- 
Dmitry.