112 lines
4.4 KiB
Groff
112 lines
4.4 KiB
Groff
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.\" Copyright (c) 1992, 1993 Eugene W. Stark
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.\" All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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.\" This product includes software developed by Eugene W. Stark.
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.\" 4. The name of the author may not be used to endorse or promote products
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.\" derived from this software without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY EUGENE W. STARK (THE AUTHOR) ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT,
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.\" INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
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.\" (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
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.\" SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.Th XTEN 8 "30 Oct 1993"
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.Dd Oct 30, 1993
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.Dt TW 4
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.Os BSD FreeBSD
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.Sh NAME
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tw \- TW-523 X-10 device driver
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.Sh DESCRIPTION
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.Nm Tw
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is the driver for the TW-523 power line interface, for use with X-10 home
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control products. The X-10 protocol is compatible with a number of home
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control systems, including Radio Shack ``Plug 'n Power(tm)'' and
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Stanley ``Lightmaker(tm).''
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.Pp
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The driver supports
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.Fn read
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.Fn write
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and
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.Fn select
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system calls.
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The driver allows multiple processes to read and write simultaneously,
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but there is probably not much sense in having more than one reader or more
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than one writer at a time, and in fact there may currently be a race
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condition in the driver if two processes try to transmit simultaneously
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(due to unsynchronized access to the sc_pkt structure in tw_sc).
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.Pp
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Transmission is done by calling
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.Fn write
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to send three byte packets of data.
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The first byte contains a four bit house code (0=A to 15=P). The second byte
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contains a five bit unit/key code (0=unit 1 to 15=unit 16, 16=All Units Off
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to 31 = Status Request). The third byte specifies the number of times the
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packet is to be transmitted without any gaps between successive transmissions.
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Normally this is 2, as per the X-10 documentation, but sometimes (e.g. for
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bright and dim codes) it can be another value. Each call to
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.Fn write
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can specify
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an arbitrary number of data bytes, but at most one packet will actually be
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processed in any call. Any incomplete packet is buffered until a subsequent
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call to
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.Fn write
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provides data to complete it. Successive calls to
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.Fn write
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leave a three-cycle gap between transmissions, per the X-10 documentation.
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The driver transmits each bit only once per half cycle, not three times as
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the X-10 documentation states, because the TW523 only provides sync on
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each power line zero crossing. So, the driver will probably not work
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properly if you have three-phase service. Most residences use a two-wire
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system, for which the driver does work.
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.Pp
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Reception is done using
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.Fn read
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The driver produces a series of three
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character packets. In each packet, the first character consists of flags,
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the second character is a four bit house code (0-15), and the third character
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is a five bit key/function code (0-31). The flags are the following:
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.Bl -diag
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.It
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#define TW_RCV_LOCAL 1 /* The packet arrived during a local transmission */
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.It
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#define TW_RCV_ERROR 2 /* An invalid/corrupted packet was received */
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.El
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.Pp
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The
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.Fn select
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system call can be used in the usual way to determine if there
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is data ready for reading.
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.Sh SEE ALSO
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.Bl -diag
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.It
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.Xr xten 1
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.It
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.Xr xtend 8
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.It
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TW-523 documentation from X-10 Inc.
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.El
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.Sh FILES
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.Bl -tag -width /dev/tw
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.It Pa /dev/tw?
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the TW523 special file
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.El
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.Sh AUTHOR
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Eugene W. Stark (stark@cs.sunysb.edu)
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