NXP Semiconductors Kinetis KE1xZ256, Reference Manual

Page: 128 / 1325

When a slave bus is being idled by the crossbar, it remains parked with the last master to
use the slave port. This is done to save the initial clock of arbitration delay that otherwise
would be seen if the same master had to arbitrate to gain control of the slave port.
9.4.2 Arbitration
The crossbar switch supports two arbitration algorithms:
• Fixed priority
• Round-robin
The selection of the global slave port arbitration algorithm is described in the crossbar
switch chip-specific information.
9.4.2.1 Arbitration during undefined length bursts
All lengths of burst accesses lock out arbitration until the last beat of the burst.
9.4.2.2 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 (for example, in a system
with 5 masters, 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:
Functional Description
Kinetis KE1xZ256 Sub-Family Reference Manual, Rev. 3, 07/2018
128 NXP Semiconductors