Small controller found on SGI Tezro, SGI Origin300, SGI Origin 3000, SGI Fuel and more recent systems. Environmental monitoring reports errors to this control. Usually has a two line LCD panel connected to that displays output from errors/commands.
From with an IRIX shell L1 commands can be issued. For example:
bash# l1 serial all
The L2 Controller can switch to an L1 controller by specifying the brick and the command "l1"