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Chapter 14 Crossbar Switch (XBAR)
MPC5602P Microcontroller Reference Manual, Rev. 4
Freescale Semiconductor
279
14.6.6.1
Fixed priority operation
When operating in fixed-priority arbitration mode, each master is assigned a unique priority level in the
XBAR_MPR. If two masters both request access to a slave port, the master with the highest priority in the
selected priority register gains control over the slave port.
Any time a master makes a request to a slave port, the slave port checks to see if the new requesting
master’s priority level is higher than that of the master that currently has control over the slave port (if any).
The slave port does an arbitration check at every clock edge to ensure that the proper master (if any) has
control of the slave port.
If the new requesting master’s priority level is higher than that of the master that currently has control of
the slave port, the higher priority master is granted control at the termination of any currently pending
access, assuming the pending transfer is not part of a burst transfer.
A new requesting master must wait until the end of the fixed-length burst transfer, before it is granted
control of the slave port. But if the new requesting master’s priority level is lower than that of the master
that currently has control of the slave port, the new requesting master is forced to wait until the master that
currently has control of the slave port is finished accessing the current slave port.
14.6.6.1.1
Parking
If no master is currently requesting the slave port, the slave port is parked. The slave port parks always to
the most recently requesting master (park-on-last). When parked on the last master, the slave port is
passing that master’s signals through to the slave bus. When the master accesses the slave port again, no
other arbitration penalties are incurred except that a one clock arbitration penalty is incurred for each
access request to the slave port made by another master port. All other masters pay a one clock penalty.