20.3.2 Arbitration
The crossbar switch supports two arbitration algorithms:
• Fixed priority
• Round robin
The selection of the global slave port arbitration is controlled by MCM_PLACR[ARB].
For fixed priority, set ARB to 0. For round robin, set ARB to 1. This arbitration setting
applies to all slave ports.
20.3.2.1 Arbitration During Undefined Length Bursts
All lengths of burst accesses lock out arbitration until the last beat of the burst.
20.3.2.2 Fixed-priority operation
When operating in fixed-priority mode, each master is assigned a unique priority level
with the highest numbered master having the highest priority (master 1 has lower priority
than master 3). If two masters request access to the same slave port, the master with the
highest priority gains control over the slave port.
NOTE
In this arbitration mode, a higher-priority master can
monopolize 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 new
requesting master's priority level is higher than that of the master that currently has
control over the slave port, unless the slave port is in a parked state. The slave port
performs 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:
Chapter 20 Crossbar Switch Lite (AXBS-Lite)
KL25 Sub-Family Reference Manual, Rev. 3, September 2012
Freescale Semiconductor, Inc. 333
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