17.4.2.2 Fixed-priority operationWhen operating in fixed-priority mode, each master is assigned a unique priority levelwith the highest numbered master having the highest priority (for example, in a systemwith 5 masters, master 1 has lower priority than master 3). If two masters request accessto the same slave port, the master with the highest priority gains control over the slaveport.NOTEIn this arbitration mode, a higher-priority master canmonopolize a slave port, preventing accesses from any lower-priority master to the port.When a master makes a request to a slave port, the slave port checks whether the newrequesting master's priority level is higher than that of the master that currently hascontrol over the slave port, unless the slave port is in a parked state. The slave portperforms an arbitration check at every clock edge to ensure that the proper master, if any,has control of the slave port.The following table describes possible scenarios based on the requesting master port:Table 17-1. How the Crossbar Switch grants control of a slave port to a masterWhen Then the Crossbar Switch grants control to therequesting masterBoth of the following are true:• The current master is not running a transfer.• The new requesting master's priority level is higher thanthat of the current master.At the next clock edgeThe requesting master's priority level is lower than the currentmaster.At the conclusion of one of the following cycles:• An IDLE cycle• A non-IDLE cycle to a location other than the currentslave port17.4.2.3 Round-robin priority operationWhen operating in round-robin mode, each master is assigned a relative priority based onthe master port number. This relative priority is compared to the master port number (ID)of the last master to perform a transfer on the slave bus. The highest priority requestingmaster becomes owner of the slave bus at the next transfer boundary. Priority is based onhow far ahead the ID of the requesting master is to the ID of the last master.Functional DescriptionKL27 Sub-Family Reference Manual , Rev. 5, 01/2016260 Freescale Semiconductor, Inc.
