i386/179115: Writing to uart1 causes host to hang

[Majdi S. Abbas]

>Number:         179115
>Category:       i386
>Synopsis:       Writing to uart1 causes host to hang
>Confidential:   no
>Severity:       non-critical
>Priority:       low
>Responsible:    freebsd-i386
>State:          open
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Thu May 30 19:40:00 UTC 2013
>Closed-Date:
>Last-Modified:
>Originator:     Majdi S. Abbas
>Release:        9.1-RELEASE
>Organization:
Lattice, L.L.C.
>Environment:
root at procyon:/dev # uname -a
FreeBSD procyon.latt.net 9.1-RELEASE FreeBSD 9.1-RELEASE #2: Wed May 29 16:01:42 UTC 2013     msa at procyon.latt.net:/usr/src/sys/i386/compile/NET4801  i386
root at procyon:/dev # dmesg | grep uart
uart0: <16550 or compatible> at port 0x3f8-0x3ff irq 4 flags 0x10 on isa0
uart0: console (9600,n,8,1)
uart1: <16550 or compatible> at port 0x2f8-0x2ff irq 3 on isa0
uart0: <16550 or compatible> at port 0x3f8-0x3ff irq 4 flags 0x10 on isa0
uart0: console (9600,n,8,1)
uart1: <16550 or compatible> at port 0x2f8-0x2ff irq 3 on isa0
>Description:
Opening /dev/cuau1 works successfully; incoming data arrives and is read just fine.  stty verifies parameters normally, and this is a standard serial port on real hardware (no USB or anything else involved here.)

Any attempt to write to /dev/cuau1 while open causes the system to hang; it returns ping and completes 3 way handshakes but is unresponsive via ssh and on console.

Same cabling, same configuration works on another OS.  Levels have been verified with a digital volt meter, and RS232 analyzer.



>How-To-Repeat:
100% repeatable with either my build or GENERIC from boottime.

>Fix:


>Release-Note:
>Audit-Trail:
>Unformatted: