Date: Mon, 21 Mar 2011 15:15:08 GMT From: Poul-Henning Kamp <phk@critter.freebsd.dk> To: FreeBSD-gnats-submit@FreeBSD.org Subject: kern/155752: tcdrain(3) does not work with uart(4) driver Message-ID: <201103211515.p2LFF8Ca027067@critter.freebsd.dk> Resent-Message-ID: <201103211540.p2LFe2wW036731@freefall.freebsd.org>
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>Number: 155752
>Category: kern
>Synopsis: tcdrain(3) does not work with uart(4) driver
>Confidential: no
>Severity: non-critical
>Priority: medium
>Responsible: freebsd-bugs
>State: open
>Quarter:
>Keywords:
>Date-Required:
>Class: sw-bug
>Submitter-Id: current-users
>Arrival-Date: Mon Mar 21 15:40:01 UTC 2011
>Closed-Date:
>Last-Modified:
>Originator: Poul-Henning Kamp
>Release: FreeBSD 9.0-CURRENT amd64
>Organization:
>Environment:
System: FreeBSD critter.freebsd.dk 9.0-CURRENT FreeBSD 9.0-CURRENT #0 r218760M: Thu Feb 17 06:36:02 UTC 2011 root@critter.freebsd.dk:/usr/obj/freebsd/head/sys/CRITTER amd64
Also affected: FreeBSD 8.1-RELEASE
>Description:
With the change from sio(4) to uart(4), tcdrain(3) broke.
Now tcdrain(3) only tests if the characters have been
delivered to the uart(4) subdriver, it does not wait for
them to have actually been sent on the wire.
This prevents half-duplex communications with CTS/RTS from
working.
This contradicts both our own manpage and The Open Group
Standards.
>How-To-Repeat:
#define AZ(x) assert ((x) == 0)
int j, fd;
fd = open(),
makeraw() etc.
set speed 300BPS
j = TIOCM_RTS;
AZ(ioctl(fd, TIOCMBIS, &j));
assert(3 == write(fd, "FOO", 3))
AZ(tcdrain(fd));
AZ(ioctl(fd, TIOCMBIC, &j));
Observe that RTS flips high + low, long before the three
characters make it out through the TXD pin.
>Fix:
There don't seem to be a newbus uart(4) method to ask or
wait until all transmitted characters have been sent.
One is obviously necessary.
>Release-Note:
>Audit-Trail:
>Unformatted:
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