An integrated circuit chip device includes monitoring circuitry for monitoring system circuitry, the monitoring circuitry having units connected in a tree-based structure for routing communications through the integrated circuit chip device. The tree-based structure has branches extending from a root unit, each branch comprising a plurality of units, each unit connected to a single unit above in the branch and a single unit below in the branch. Communications are routable between the root unit and a destination unit of a branch via intermediate units of that branch. Crosslinks connect corresponding units of adjacent branches, each crosslink can be enabled to route communications between the root unit and a destination unit of one of the branches the crosslink connects via the other branch the crosslink connects in response to an intermediate unit being deemed defective, that intermediate unit being in the same branch as the destination unit.