The SCB bus arbitration is fixed and not programmable but, each slave does have a quality of service (QoS) programmable feature that affects arbitration.
Each slave interface has a QoS value (or priority) associated with its read and write channels.At the entry point to the infrastructure, all transactions are allocated a programmable, local QoS value. The arbitration of the transaction throughout the infrastructure uses this QoS. At any arbitration node, a fixed priority exists for transactions with a different QoS. The highest value has the highest priority. If there are coincident transactions at an arbitration node with the same QoS value that require arbitration, then the network uses a least recently used (LRU) algorithm. At each switch, the master with highest QOS gains access, and that switch output takes the winner’s QoS value for that transaction. At the next switch slave
interface, that master uses the winner’s QoS value.