Does the serial driver (kernel 2.2.12, Intel) still drop characters

George T. Talbot (george@moberg.com)
Thu, 28 Oct 1999 22:06:20 +0000

I've got this touchscreen industrial PC that I'm using that's basically laptop hardware with a
touchscreen. It's got 16550A UARTS. The problem I'm having is that I've got a serial device that
pumps data into a serial port at 38.4Kbaud, and when the kernel swaps something in or out, more
likely than not, the serial driver will lose a character or two.

I searched the archives and found two threads:

"2.2.12 serial driver swapping characters?" (circa Sept. 99)

In this thread started by Ulrich Windl <ulrich.windl@rz.uni-regensburg.de>,
there's a discussion about how the serial drivers got weird at 2.2.11+. Sounds
a whole lot like what's happening to me.

"pre-patch-2.0.31 try_to_free_page() messages" (circa June 97)

There's a rather fascinating message from Ted T'so discussing an intentional
workaround for crappy IDE controllers that causes the serial driver to lose
characters. ( http://www.uwsg.indiana.edu/hypermail/linux/kernel/9706.0/0075.html )

Anybody (Ted, maybe) know if the fix described in the June 97 post works with current
kernels? Did something else happen to the serial driver? I fear doing what Ted suggests
in the post, as he warns of "MASSIVE FILESYSTEM DAMAGE".

I've got a reasonably good test setup here for repeating this problem if anyone's interested. I
do not have a reasonable picture of how the serial driver works, however.

Please CC me in replies to this thread, as I can't read fast enough to subscribe to the list.

Thanks.

--
George T. Talbot
<george@moberg.com>


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