Onno Chess Software : Engine Options

Access to the Engine Options

How you access the engine options, depends on your GUI.

In Arena, right click in the engine window when Onno is loaded. Select Configure Onno.

In SCID, from the Tools menu, select Analysis Engine. Then select Onno and press Edit. A new window should pop up. Press the button Configure UCI engine there.

For other GUIs consult their documentation.

Specific Options

Currently, Onno has the following specific options.

• Log Level: This option is for debugging in GUIs that do not offer a logging option. When the Log Level is set to a nonzero value, Onno writes a file like onno-20091231-180000.log (example means New Year's Eve, 6pm) in the directory where the Onno executable is installed. If this file cannot be written (e.g. lack of permissions), no logfile is written, but Onno continues to work normally.

  The Log Levels mean:

  • Level 0: No logfile written (default).
  • Level 1: Logs all received commands and all output except for intermediate output during search (recommended for debugging).
  • Level 2: Logs everything. Might slow down the engine.

• Verbose Level: By default, Onno prints some extra information (using the UCI command "info string"). Also, Onno can print information in early stages of search. This parameter adjusts the amount of output. This is not to be mixed with a debugging option; even on the highest Verbose Level only few important messages are printed.

  The Verbose Levels mean:

  • Level 0: Do not print any extra information.
  • Level 1: Only print error messages.
  • Level 2: Print error messages and warnings.
  • Level 3: Print all extra information (default).
  • Level 4: Print all extra information and some output in early stages of search.
  • Level 5: Print all extra information and all output in early stages of search.

  Note that levels 4 and 5 may lead to problems in some GUIs.

• Flush Debug: Some steps in engine initialization cause messages (e.g. a message which tablebases are found). Unlike later messages they are not sent to the GUI automatically, because some GUIs display them in annoying pop up windows. The engine remembers these messages and sends them when this button is pressed.

  This button works only when the Verbose Level is at least 3.

• Show Full Path: Available in 1-0-3 and later. In the very moment where this option is set, Onno passes the path to the running Onno executable to the GUI using info string. Most GUIs will display it.

  This is useful if you have different copies of Onno installed. Save your engine options in the GUI, this option checked. The GUI will pass the engine options to Onno at startup, so Onno will output its path then.

• Random Intensity: Onno can randomize its search. That means you can make it compute different results on the same position. This parameter adjusts the amount of randomness. 0 turns randomness completely off.

  Please note:

  • In multi processor mode (i.e. Threads set to a value greater then 1), the search in inherently non-deterministic. This is not affected by setting random intensity to 0.
  • To get really different results by randomization you also need to choose a different Random Seed or set Random Seed to -1.

• Random Seed: When the search is randomized by the option Random Intensity, the seed initializes the internal random generator.

  That means that if you use the same value for Random Seed, you will be able to reproduce even randomized results on a specific position. If you use a different seed, you may get different results.

  Normal seed values range from 0 to 32767. The seed value -1 has a special meaning: The engine chooses a value between 0 and 32767 automatically, based on the system clock. This should lead to different seeds at every engine start. You can see what seed has been chosen when you press "Flush Debug".

  The "size" of the seed has absolutely no meaning. Onno plays the same style with a seed of 0 and a seed of 10000.

• Threads: Number of CPU cores that do a search. The maximum possible value for this option is the minimum of

  • 1, if you are using the single processor version of Onno
  • number of physical cores on your machine
  • 8

  If you have a single processor license, setting Threads to more than 1 has no effect.

• TB Min Depth: Available in 1-1-0 and later. Onno will probe the tablebases instead of a search when the search depth at a node is larger or equal to this value.

  Which value is best for you depends on the number of threads and on your access speed to the tablebases. The default of 6 was found to be good for one thread and tablebases on hard disc. If you have the tablebases on a ramdisc you might want to decrease min depth (access tablebases more often). If you use more threads you might want to increase the min depth (access tablebases less often).

• TB Draw: Available in 1-1-0 and later. This option tells the engine what to do if the position on the board is a draw according to tablebases.

  Possible values are:

  • move instantly: Onno does not try to make it as hard as possible for the opponent to draw the game. It just quickly plays any move that maintains the draw. This is the right setting if your opponent also has tablebases and he might try to win on time.
  • null scores (default): Onno only takes moves into consideration that maintain the draw, but computes the hardest move among these. Onno gives a score of 0. This is the right setting if your oppontent does not have tablebases.
  • ignore: Onno only takes moves into consideration that maintain the draw, but computes the hardest move among these. Onno ignores the tablebases for the score, i.e. might give a nonzero score. This is the right setting if you want to understand Onno's analysis of the position.

General Options

Onno supports some generic UCI options A knowledgeable GUI will hide some of them from you and access them automatically. If you cannot see these options, you can simply ignore them.

Those options are:

• Hash: Size of hash table in MB. The hash table is a memory for positions that already have been searched.

  In the 32 bit version of Onno and in versions 1-0-2 and below at most 1024 MB are possible. In the 64 bit versions starting from 1-0-3 at most 16.384 MB are possible.

  Please note: You should choose the hash small enough to fit into your physical memory together with all currently executed programs. You should not make the hash larger then the search can fill. The latter is only a relevant bound if you play at very fast time controls. Watch the display of the hash fill degree in your GUI.

  Onno accepts only 0, 1, and doubling steps, i.e. (0), (1), (2), 4, 8, 16, 32, 64, 128, 256, 512, 1024, (2048), (4096), (8192), (16384) megabyte. Not all GUIs accept values below 4 MB. Intermediate values are rounded down by Onno to the next lower value.

• Clear Hash: Clears the hash table.

• Ponder: Tells the engine in a game that it can expect to be allowed to ponder (think on opponent's time). This is used for time management only, it does not actually cause pondering.

• MultiPV: Makes the engine compute not only the best move, but the n best moves, where n is the value of MultiPV.

• UCI_ShowCurrLine: Makes the engine periodically print the line that it is currently calculating.

• UCI_ShowRefutations: Makes the engine print expected replies on each of its possible moves.

• UCI_EngineAbout: This is a dummy option whose only purpose is to contain some textual information about the engine as default. Setting this option has no effect.

• NalimovPath: Available in 1-1-0 and later. Path to Nalimov endgame tablebases. Multiple paths must be separated by comma (,) or semicolon (;).

• NalimovCache: Available in 1-1-0 and later. Size of memory cache for Nalimov tablebases in megabytes.