Freescale Semiconductor MPC5553 - Functional Description

MPC5553/MPC5554 Microcontroller Reference Manual, Rev. 5
7-8 Freescale Semiconductor
7.3 Functional Description
This section describes the functionality of the XBAR in more detail.
7.3.1 Overview
The main goal of the XBAR is to increase overall system performance by allowing multiple masters to
communicate concurrently with multiple slaves. In order to maximize data throughput it is essential to
keep arbitration delays to a minimum.
This section examines data throughput from the point of view of masters and slaves, detailing when the
XBAR will stall masters, or insert bubbles on the slave side.
7.3.2 General Operation
When a master makes an access to the XBAR from an idle master state, the access will be taken
immediately by the XBAR. If the targeted slave port of the access is available (that is, the requesting
master is currently granted ownership of the slave port), the access will be immediately presented on the
slave port. It is possible to make single clock (zero wait state) accesses through the XBAR by a granted
master. If the targeted slave port of the access is busy or parked on a different master port, the requesting
master will simply see wait states inserted until the targeted slave port can service the master’s request.
The latency in servicing the request will depend on each master’s priority level and the responding slave’s
access time.
Because the XBAR appears to be just another slave to the master device, the master device will have no
knowledge of whether or not it actually owns the slave port it is targeting. While the master does not have
control of the slave port it is targeting it will simply be wait-stated.
A master will be given control of a targeted slave port only after a previous access to a different slave port
has completed, regardless of its priority on the newly targeted slave port. This prevents deadlock from
occurring when a master has an outstanding request to slave port A that has a long response time, has a
pending access to a different slave port B, and a lower priority master also makes a request to the different
28 — Reserved.
29–31 PARK Park. Used to determine which master port this slave port parks on when no masters are
actively making requests. PCTL must be set to 00.
000 Park on master port 0
001 Park on master port 1
010 Park on master port 2
011 Park on master port 3 (Applies to MPC5553 only)
100 Illegal master port
101 Illegal master port
110 Illegal master port
111 Illegal master port
Table 7-4. XBAR_SGPCRn Field Descriptions (Continued)
Bits Name Description