Problem detecting and reacting to serial break

[Garrett Cooper]

On Sat, Aug 14, 2010 at 5:03 PM, Paul Thornton <prt at prt.org> wrote:
> Ed Schouten wrote:
>> * Paul Thornton <prt at prt.org> wrote:
>>> I'm using 8.0-RELEASE with uftdi and ucom driving the serial port.
>>
>> Somewhat unrelated question: have you ever tried running the this code
>> on 7.x? If so, did it work?
>
> I've just tried this on 7.2-RELEASE (that was the only 7.x CD I could
> find lurking about my desk).
>
> Something is clearly quite different between 7 and 8 here:
>
> On 7.2, it doesn't like my tcsetattr:
>
> [root at test1 /usr/local/src]# ./dmxrx2
> Opened /dev/cuaU0 on file handle 3
> before: c_iflag=2106 c_oflag=3 c_cflag=cf00 c_lflag=400
> tcsetattr: Invalid argument
>
> No amount of fiddling with the options would make it work, so I used
> stty to set the paramaters of /dev/cuaU0.init to what I wanted:
>
> stty -f /dev/cuaU0.init speed 250000 -icanon -isig -echo cs8 clocal
>  cstopb cread ignpar -ixany -ixon -ixoff -ignbrk brkint -imaxbel -icrnl
>
> ... and re-ran with some more debug ...
>
> [root at test1 /usr/local/src]# ./dmxrx2
> Opened /dev/cuaU0 on file handle 3
> before: c_iflag=6 c_oflag=3 c_cflag=cf00 c_lflag=400
> tcsetattr: Invalid argument
> after: c_iflag=6 c_oflag=3 c_cflag=8f00 c_lflag=400
> calling read with 513 bytes to go
> ^CCaught a signal: 2
>
> So I now hang in a blocked read().
>
> A quick and dirty test of "hd /dev/cuaU0" gives one line of zeros and
> then hangs.  Under 8.0, this continually dumps the data coming in as you
> might expect it to.
>
> Were there any significant serial changes between 7.x and 8.0 which
> might explain this?  I don't have enough understanding of how FreeBSD's
> serial internals should work to debug this on my own, but am more than
> happy to try all suggestions made.

Bits of syscons were largely rewritten between 7.x and 8.x. That's the
reason why Ed ask the question :) (he did the rewriting).

-Garrett