PXR40RM Datasheet, PDF (433/1434 Pages) Freescale Semiconductor, Inc – PXR40 Microcontroller

Chapter 14
AMBA Crossbar Switch (XBAR)
14.1 Introduction
This chapter describes the multi-port crossbar switch (XBAR), which supports simultaneous connections
between master ports and slave ports. XBAR supports a 32-bit address bus width and a 64-bit data bus
width at all master and slave ports and runs at half the system frequency.
14.1.1 Overview
The XBAR allows concurrent transactions to occur from any master port to any slave port. It is possible
for all master ports and slave ports to be in use at the same time as a result of independent master requests.
If a slave port is simultaneously requested by more than one master port, arbitration logic selects the higher
priority master and grant it ownership of the slave port. All other masters requesting that slave port are
stalled until the higher priority master completes its transactions.
By default, requesting masters are granted access based on a fixed priority. A round-robin priority mode
also is available. In this mode, requesting masters are treated with equal priority and are granted access to
a slave port in round-robin fashion, based upon the ID of the last master to be granted access. A block
diagram of the XBAR is shown in Figure 14-1.
The XBAR can place a slave port in a low-power park mode to avoid dissipating any power transitional
address, control or data signals when the master port is not actively accessing the slave port. There is a
one-cycle arbitration overhead for exiting low-power park mode.
Freescale Semiconductor
PXR40 Microcontroller Reference Manual, Rev. 1
14-1