"level" command is improperly used

[jdart1]

xboard engines expect to receive a "level" command to set the time control.

This command should be sent only once at the start of a new game (typically after "new") and subsequently if the time control changes (for example, at the expiration of an initial time control such as 40/2 and the beginning of a new one for the next n moves).

However, lichess-bot sends "level" after each move and apparently reduces the time control section of that command by the time used. For example I see: level 0 4:57 3.0 at the start of a 5+3 time control game and then after each next move I see different quantities in the time control field, for example: level 0 4:32 3.0 after a few moves. This is incorrect behavior. The level command is for setting the time control for a game or a portion of a game. The "time" and "otim" commands inform the engine after each move of its own and its opponent's time remaining.

[MarkZH]

I had a discussion about this issue with the python-chess developer in this issue. We concluded that while sending level for every move is non-standard, it should be harmless. Are the extra level commands causing problems for your engine?

[jdart1]

My program can record games played, and when it does, it outputs the time control used. So the way I found this issue was that all the games had random, usually low, time controls in the game output that were not the real game time control. That is not maybe a big issue. But note also the CECP specification is quite clear about the semantics of "level:" in the case where the first number is zero, the next number is not the minutes left in the game. The spec says:

The command to set an incremental time control looks like this:

level 0 2 12 Here the 0 means "play the whole game in this time control period", the 2 means "base=2 minutes", and the 12 means "inc=12 seconds". As in conventional clock mode, the second argument to level can be in minutes and seconds.

[jdart1]

Winboard, which is really the reference implementation of the protocol, has never sent multiple level commands per game, except when the game is divided into multiple different time control periods.