I'd like to hear from everyone who is trying to interface their own
-chess engine to xboard/WinBoard. Please email me,
-tim@tim-mann.org. Also, please join
-the mailing list for authors of xboard/WinBoard compatible chess
-engines. The list is now hosted by Yahoo Groups; you can join at http://www.egroups.com/group/chess-engines, or you can read the
+chess engine to xboard/WinBoard. Please join the mailing list for
+authors of xboard/WinBoard compatible chess engines and post a message
+about what you're doing. The list is now hosted by Yahoo Groups; you
+can join at http://groups.yahoo.com/group/chess-engines, or you can read the
list there without joining. The list is filtered to prevent spam.
| unknown | Unknown variant (not supported)
@@ -618,7 +617,20 @@ below.
sd DEPTH
The engine should limit its thinking to DEPTH ply.
The commands "level" or "st" and "sd" can be used together in an orthogonal way.
-If both are issued, the engine should observe both limitations.
+If both are issued, the engine should observe both limitations:
+In the protocol, the "sd" command isn't a time control. It doesn't
+say that your engine has unlimited time but must search to exactly the
+given depth. It says that you should pay attention to the time
+control as normal, but cut off the search at the specified depth even
+if you have time to search deeper. If you don't have time to search
+to the specified depth, given your normal time management algorithm,
+then you will want to stop sooner than the given depth.
+
+The "new" command should set the search depth back to unlimited. This
+is already stated in the spec. The "level" command should not affect
+the search depth. As it happens, xboard/WinBoard currently always
+sends sd (if needed) right after level, but that isn't part of the
+spec.
nps NODE_RATE
@@ -821,9 +833,16 @@ The setboard command is the new way to set up positions, beginning
in protocol version 2. It is not used unless it has been selected
with the feature command. Here FEN is a position in Forsythe-Edwards
Notation, as defined in the PGN standard.
-In FRC or CRC, WinBoard will use Shredder-FEN or X-FEN standard,
-i.e. it can use the rook-file indicator letter to represent a castling right (like HAha)
-whenever it wants, but if it uses KQkq, this will always refer to the outermost rook on the given side
+Note that this PGN standard referred to here
+only applies to normal Chess;
+Obviously in variants that cannot be described by a FEN for normal Chess,
+e.g. because the board is not 8x8, other pieces then PNBRQK participate,
+there are holdings that need to be specified, etc.,
+xboard will use a FEN format that is standard or suitable for that varant.
+In particular, in FRC or CRC, WinBoard will use Shredder-FEN or X-FEN standard,
+i.e. it can use the rook-file indicator letter to represent a castling right
+(like HAha) whenever it wants, but if it uses KQkq, this will always refer
+to the outermost rook on the given side.
Illegal positions: Note that either setboard or edit can
@@ -1019,8 +1038,8 @@ the engine has to decide for itself
how to divide up the available memory between the various tables it wants to use
(e.g. main hash, pawn hash, tablebase cache, bitbases).
This command will only be sent to engines that have requested it through the memory feature,
-and only at the beginning of a game
-(before any moves have been done).
+and only at the start of a game,
+as the first of the commands to relay engine option settings just before each "new" command.
@@ -1032,7 +1051,9 @@ This could be interpreted as the number of search threads for SMP engines.
This command will only be sent to engines that have requested it through the smp feature.
The engine should be able to respond to the "cores" command any time during a game,
but it is allowed to finish a search in progress before procesing the command.
-(Reaction during ponder time should be immediate, though.)
+(Obeying the command should take priority over finishing a ponder search, though.)
+In any case it will be sent at the start of every game
+as the last command to relay engine option settings before the "new" command.
@@ -1052,6 +1073,27 @@ but could also be the name of a file, or in fact anything the particular EGT typ
It is upto the developer of the EGT format to specify the syntax of this parameter.
This command will only be sent to engines that have told the GUI they support EGTs of the given TYPE
through the egt feature.
+It will be sent at the start of each game, before the "new" command.
+
+
+
+ option NAME[=VALUE]
+
+This command changes the setting of the option NAME defined by the engine
+(through an earlier feature command)
+to the given VALUE.
+XBoard will in general have no idea what the option means,
+and will send the command only when a user changes the value of this option through a menu,
+or at startup of the engine
+(before the first 'cores' command or, if that is not sent, the first 'new' command)
+in reaction to command-line options.
+The NAME echoes back to the engine the string that was identified as an option NAME
+in the feature command defining the option.
+The VALUE is of the type (numeric or text or absent) that was implied by the option type
+specified in this feature command,
+i.e. with 'spin' and 'check' options VALUE will be a decimal integer (in the latter case 0 or 1),
+with 'combo' and 'string' options VALUE will be a text string,
+and with 'button' and 'save' options no VALUE will be sent at all.
@@ -1391,6 +1433,8 @@ will be set by the GUI through the "memory" command.
If smp=1, the GUI will send the "cores" command to the engine to inform it how many CPU cores it can use.
+Note that sending smp=1 does not imply the engine can use more than one CPU;
+just that it wants to receive the "cores" command.
@@ -1404,6 +1448,50 @@ If you do not set this feature, xboard will assume the engine does not support e
and will not send any "egtpath" commands to inform the engine about their whereabouts.
+
+option (string, see text below)
+
+
+This feature is used by the engine to define an option command to appear in a GUI menu,
+so that the user can change the corresponding setting of the engine through the GUI.
+The string describes the option by defining a name, type, current value and (sometimes) the acceptable value range.
+There are nine different options types, each requiring a slighly different syntax of the defining string:
+
+feature option="NAME -button"
+
+feature option="NAME -save"
+
+feature option="NAME -check VALUE"
+
+feature option="NAME -string VALUE"
+
+feature option="NAME -spin VALUE MIN MAX"
+
+feature option="NAME -combo CHOICE1 /// CHOICE2 ..."
+
+feature option="NAME -slider VALUE MIN MAX"
+
+feature option="NAME -file VALUE"
+
+feature option="NAME -path VALUE"
+
+NAME is an arbitrary alphanumeric string which can contain spaces;
+the other words in capitals would be replaced by the current (default) setting of the option,
+(a character string for -string options, a decimal number for -spin and -check options,
+were the latter uses 1=checked, 0=unchecked),
+the minimum or maximum value of numeric (-spin) options,
+or arbitrary text labels (for -combo option).
+In the latter case, the current value will be preceded by an asterisk.
+The -file and -path options are similar to -string, but can be used to inform the GUI that
+the text represents a file name or folder name respectively, so the GUI dialog to set it
+could add the appropriate browse button to the text-edit field.
+Similarly, a -slider option is like a -spin, but the GUI might make a different
+graphical representation for it.
+A -save option is like a -button, and defines an immediate command to be sent by the engine.
+With -save the GUI will make sure all current option settings are flushed to the engine
+before it sends this command.
+
+
done (integer, no default)
@@ -1505,9 +1593,26 @@ Machines mode, and the PGN save file as required.
will be taken by WinBoard as an unconditional refusal of the engine to play on,
which might cause you to forfeit if the game was in fact not over.
This command should thus not be used to offer draws, accept draws,
-or make draw-by-rule claims that might not be valid
-(because it is not your move, and the opponent already moved without you knowing it yet).
-For offering and claiming draws, "offer draw" should be used.
+or make draw-by-rule claims that are not yet valid in the current position
+(but will be after you move).
+For offering and claiming such draws, "offer draw" should be used.
+
+
+Note that (in accordance with FIDE rules) only KK, KNK, KBK and KBKB with all bishops on the
+same color can be claimed as draws on the basis of insufficient mating material.
+The end-games KNNK, KBKN, KNKN and KBKB with unlike bishops do have mate positions,
+and cannot be claimed.
+Complex draws based on locked Pawn chains will not be recognized as draws by most interfaces,
+so do not claim in such positions, but just offer a draw or play on.
+
+
+
+Note to GUI programmers: RESULT commands that the engine sends immediately after its move
+might be detected by the GUI only after the opponent has moved, because of communication
+and scheduling delays, no matter how fast the engine sent it.
+Any judgement of the validity of RESULT claims based on te "current" board position
+will have to account for this uncertainty.
+
resign
@@ -1516,6 +1621,8 @@ Alternatively, it can use the "RESULT {comment}" command if the string
"resign" is included in the comment; for example "0-1 {White
resigns}". xboard relays the resignation to the user, the ICS, the
other engine in Two Machines mode, and the PGN save file as required.
+Note that many interfaces work more smoothly if you resign before
+you move.
offer draw
@@ -1527,7 +1634,7 @@ Machine Black, or Two Machines mode, the offer is considered valid
until your engine has made two more moves.
This command must also be used to accept a draw offer.
Do not use the 1/2-1/2 command for that, as the offer might be no longer valid,
-in which case a refusal to play on implied by the RESULT command would make you forfeit the game.
+in which case a refusal to play on implied by the RESULT command might make you forfeit the game.
"offer draw" should also be used to claim 50-move and 3-fold-repetition draws
that will occur after your move, by sending it before making the move.
WinBoard will grant draw offers without the opponent having any say in
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