Serge NOEL
292 lines
13 KiB
Plaintext
292 lines
13 KiB
Plaintext
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<title>JMRI Hardware Support - Enhanced LocoNet® Slots</title>
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<meta name="author" content="B. Milhaupt">
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<meta name="keywords" content="Digitrax LocoNet Slot"><!--#include virtual="/help/en/parts/Style.shtml" -->
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<div id="mainContent">
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<h1>Hardware Support: Enhanced LocoNet® Slots</h1>
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<h2>Contents</h2>
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<ul>
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<li>
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<a href="#Introduction">Introduction</a>
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</li>
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<li>
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<a href="#QandA">Enhanced slots described via Questions and Answers</a>
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<ul>
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<li>
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<a href="#generalideas">What is a LocoNet "Slot"?"</a>
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</li>
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<li>
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<a href="#WhatsInIt">What's in a slot?</a>
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</li>
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<li>
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<a href="#whyImportant">Why are slots important?</a>
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</li>
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<li>
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<a href="#whyDifferent">Why is there a difference between "traditional" and
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"enhanced" LocoNet slots?</a>
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</li>
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<li>
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<a href="#ExpandEnhanceEtc">Why do you use the term "Enhanced" slots when Digitrax
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uses the term "Expanded" slots?</a>
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</li>
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<li>
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<a href="#PrimaryDiff">What are the primary differences between "Traditional" and
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"Enhanced" LocoNet slots?</a>
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</li>
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<li>
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<a href="#whatCmdStnsTrad">What command stations implement "traditional" slots?</a>
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</li>
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<li>
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<a href="#whatCmdStnsEnh">What command stations implement "enhanced" slots?</a>
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</li>
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<li>
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<a href="#whatThrotTrad">What throttles can make use of "traditional" slots?</a>
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</li>
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<li>
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<a href="#whatThrotEnh">What throttles can make use of "enhanced" slots?</a>
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</li>
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</ul>
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</li>
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<li>
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<a href="#whyNot">JMRI does not directly support "enhanced" slots. Why not?</a>
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</li>
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<li>
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<a href="#someSupport">There really is some JMRI support for "enhanced" slots. Why is
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that?</a>
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</li>
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<li>
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<a href="#whatItWillTake">What will it take for JMRI to fully support "enhanced"
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slots?</a>
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</li>
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</ul>
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<h2 id="Introduction">Introduction</h2>
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<p>This help page is presented as a set of "questions and answers". It is hoped that this
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presentation will answer the basic questions related to LocoNet "Enhanced" slots.</p>
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<h2 id="QandA">Enhanced slots described via Questions and Answers</h2>
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<h3 id="generalideas">What is a LocoNet "Slot"?</h3>
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<p>LocoNet implements the "slot" as the basic mechanism for:</p>
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<ul>
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<li>managing locomotives and the information used when sending a DCC signal to that
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locomotive;</li>
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<li>managing how locomotives may be grouped together into a consist;</li>
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<li>other system-specific uses.</li>
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</ul>
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<p>This discussion focuses on the first two of these items, and ignores the last item.</p>
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<h2 id="WhatsInIt">What's in a slot?</h2>
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<p>Locomotive control and locomotive consisting slots are those slots which may contain valid
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locomotive information. Valid locomotive information includes the slot's status, a DCC mobile
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decoder address, the decoder's current speed and direction, some stored information on which
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functions are active, the type of DCC packet to be sent to the DCC mobile decoder, the
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"Throttle ID" reported by the last throttle to acquire the slot, and position in a consist
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(if consisted).</p>
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<h2 id="whyImportant">Why are slots important?</h2>
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<p>When a LocoNet throttle acquires a locomotive address, it effectively asks the command
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station for a slot number with which to control a locomotive address. Once acquired, the
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throttle uses that <strong>slot number</strong> reported by the command station.</p>
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<h2 id="whyDifferent">Why is there a difference between "traditional" and "enhanced" LocoNet
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slots?</h2>
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<p>Some guess that limited available memory in the microcontroller devices used in early
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Digitrax command stations forced a limit of the available number of slots and amount of
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information in each slot.</p>
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<p>Some guess that LocoNet designers worried about available data throughput on LocoNet if
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locomotive control messages required more bytes.</p>
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<p>While both of these arguments are logical, only the architects of LocoNet can really know.
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But it is known that the "traditional" slot architecture placed a practical limit of up to
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120 addressable locos (whether separately controlled or consisted using "basic" consisting).
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The "enhanced" slot architecture has extended that capability to be greater than 120 in cases
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where the command station supports more than 120 locomotive-control slots.</p>
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<h2 id="ExpandEnhanceEtc">Why do you use the term "Enhanced" slots when Digitrax uses the
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term "Expanded" slots?</h2>
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<p>Upon its introduction, the primary DCS240 selling point seen by users on the
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Digitrax-Users "Yahoo" list (now the Digitrax-Users "groups.io" list) was the ability to use
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up to 400 throttles and control up to 400 locomotives. This association was well-established
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before the release of the DCS210 and DCS52 command stations.</p>
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<p>Why is this significant? Because neither the DCS210 nor the DCS52 could control more
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locomotives than a "standard-slot-only" command station, nor could they support any more
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throttles than such a command station. But both command stations use and understand the
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LocoNet messages which makes it possible for the DCS240 to support as many as 400 throttles
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and as many as 400 uniquely controllable locos.</p>
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<p>This emphasized that the so-called "expanded" slot is more than simply a mechanism which
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allows a LocoNet-based system to use more than 120 throttles, and allow the system to control
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more than 120 unique locomotives. Instead, it is an "ecosystem" which allows different
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LocoNet messaging for loco control, different throttle "steal" behavior, different command
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station memory of function states, etc.</p>
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<p>So, for the purposes of this discussion, an "enhanced" slot is one which uses newer
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LocoNet messaging to implement the additional features listed in the previous paragraph,
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regardless of the slot number value. So-called "enhanced" slot LocoNet messaging may use slot
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numbering in the "traditional" slot numbering range, as is done by the DCS210 and DCS52
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command stations, or by the DCS240 if it is configured to limit its slots to a maximum of
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120. That same "enhanced" slot LocoNet messaging may use slot numbers in the "expanded" slot
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numbering range to control those locomotives which are held in a DCS240 in a slot number
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which is above the "traditional" slot numbering range.</p>
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<h2 id="PrimaryDiff">What are the primary differences between "Traditional" and "Enhanced"
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LocoNet slots?</h2>
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There are four primary differences between "traditional" and "enhanced" LocoNet slots:
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<table border="2">
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<tr>
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<td style="text-align: center"><strong>Traditional slots:</strong>
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</td>
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<td style="text-align: center"><strong>Enhanced slots:</strong>
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</td>
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</tr>
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<tr>
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<td>use locomotive control slot numbers between 1 and 120 (or less, depending on command
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station), using a 4-byte message;</td>
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<td>use locomotive control slot numbers between 1 and 400 (or less, depending on command
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station), using 6-byte messages;</td>
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</tr>
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<tr>
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<td>remember only F0 thru F8</td>
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<td>remember F0 thru F28</td>
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</tr>
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<tr>
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<td>can be "shared" between multiple throttles;</td>
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<td>can be "stolen" by another throttle and the first enhanced-slot throttle no longer
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has control of the slot ("StealZap");</td>
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</tr>
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<tr>
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<td>can be controlled by "traditional-slot" throttles or by "enhanced-slot-capable"
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throttles;</td>
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<td>can be controlled only by "enhanced-slot-capable" throttles;</td>
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</tr>
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<tr>
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<td>can be managed by all Digitrax command stations.</td>
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<td>can only be managed by newer Digitrax command station models.</td>
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</tr>
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</table>
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<h2 id="whatCmdStnsTrad">What command stations implement "traditional" slots?</h2>
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<p>All LocoNet-compatible command stations implement traditional slots.</p>
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<h2 id="whatCmdStnsEnh">What command stations implement "enhanced" slots?</h2>
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<p>It is believed that a "LocoNet 2.0" specification defines the "enhanced" slot
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functionality. As of this writing, the Digitrax DCS52, DCS210, and DCS240 command stations
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implement "enhanced" slot functionality.</p>
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<h2 id="whatThrotTrad">What throttles can make use of "traditional" slots?</h2>
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<p>It is believed that all LocoNet-compatible throttles can make use of traditional slots to
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control locomotives and/or consists.</p>
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<h2 id="whatThrotEnh">What throttles can make use of "enhanced" slots?</h2>
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<p>As of this writing, the Digitrax DT402-series and DT500-series throttles can make use of
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"enhanced" slots. It is believed that the throttle must be configured to allow it to request
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and use "enhanced" slots - if not configured to use "enhanced" slots, or if the command
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station does not support "enhanced" slots, the throttle will make use of "traditional"
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slots.</p>
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<p>It is believed that those WiFi throttles managed by the Digitrax LNWI device can make use
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of "enhanced" slots, assuming that the command station supports "enhanced" slots.</p>
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<h2 id="whyNot">JMRI does not directly support "enhanced" slots. Why not?</h2>
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<p>It's hard to support "enhanced" slots for a variety of reasons. Primarily, "enhanced"
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slots add a large number of "boundary conditions" that are difficult to manage. And different
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Digitrax command stations seem to behave differently when "enhanced" slots are used and
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certain "boundary conditions" are exercised. Until these boundary conditions are fully
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understood, it has been deemed inappropriate to provide enhanced slot support in JMRI. This
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means that JMRI will not, at this time, control locomotives or consists using "enhanced" slot
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LocoNet messaging.</p>
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<h2 id="someSupport">There really is some JMRI support for "enhanced" slots. Why is
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that?</h2>
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<p>A few JMRI developers have reverse-engineered the apparent behavior of some aspects of
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"enhanced" slot functionality. As of this writing, that has been limited primarily to the
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"LocoNet Monitor" feature. It has been thought that any improper behavior of the "LocoNet
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Monitor" functionality at "boundary conditions" would only give an incorrect display in the
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LocoNet Monitor window but cannot cause JMRI to misbehave.</p>
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<p>As of this writing, other places where JMRI makes use of "enhanced" slots is limited to
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usage where configuration and operations are done via "enhanced" slot messaging. Any improper
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behavior due to "boundary condition" cases for these implementations is thought to not affect
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the ability of JMRI to control trains.</p>
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<h2 id="whatItWillTake">What will it take for JMRI to fully support "enhanced" slots?</h2>
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<p>There are a few things at play here. At a minimum, JMRI will require:</p>
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<ul>
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<li>greater understanding by JMRI developers of the behavior of command stations and
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throttles, for various boundary conditions, across different command station and throttle
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implementations;</li>
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<li>an understanding of proper JMRI behavior when both enhanced and traditional slots are
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used;</li>
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<li>an understanding of how slots "transition" between traditional and enhanced;</li>
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<li>some "refactoring" of JMRI's LocoNet code base, to allow for easy management of the
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"enhanced" slot type;</li>
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<li>a mechanism to provide the user some level of control of enhanced slot usage (when
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enhanced slots are available);</li>
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<li>a re-work of the LocoNet "Monitor Slots" tool to handle the potentially huge number of
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enhanced slots.</li>
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</ul>
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