Crossbar Switch (XBAR)MPC5566 Microcontroller Reference Manual, Rev. 27-8 Freescale Semiconductor7.3 Functional DescriptionThis section describes the functionality of the XBAR in more detail.7.3.1 OverviewThe main goal of the XBAR is to increase overall system performance by allowing multiple masters tocommunicate concurrently with multiple slaves. To maximize data throughput, it is essential to keeparbitration delays to a minimum.This section examines data throughput from the point of view of masters and slaves, detailing when theXBAR stalls masters, or inserts bubbles on the slave side.7.3.2 General OperationWhen a master makes an access to the XBAR from an idle master state, the access is taken immediatelyby the XBAR. If the targeted slave port of the access is available (that is, the requesting master is currentlygranted ownership of the slave port), the access is immediately presented on the slave port. It is possibleto make single clock (zero wait state) accesses through the XBAR by a granted master. If the targeted slaveport of the access is busy or parked on a different master port, the requesting master receives wait statesuntil the targeted slave port can service the master request. The latency in servicing the request dependson each master’s priority level and the responding slave’s access time.Because the XBAR appears to be simply another slave to the master device, the master device has noindication that it owns the slave port it is targeting. While the master does not have control of the slave portit is targeting, it is wait-stated.A master is given control of a targeted slave port only after a previous access to a different slave port hascompleted, regardless of its priority on the newly targeted slave port. This prevents deadlock fromoccurring when a master has the following conditions:• Outstanding request to slave port A that has a long response time• Pending access to a different slave port B• Lower priority master also makes a request to the different slave port B.28 Reserved, must be cleared.29–31PARKPark. Used to determine which master port this slave port parks on when no masters are actively makingrequests. PCTL must be set to 00.000 Park on master port 0001 Park on master port 1010 Park on master port 2011 Park on master port 3100 Invalid value101 Invalid value110 Invalid value111 Invalid valueTable 7-5. XBAR_SGPCRn Field Descriptions (continued)Field Description
