Arbitration - Freescale Semiconductor MCF5329 Reference Manual

Crossbar Switch (XBS)
Field
31 Read only. Forces both of the slave port's registers (XBS_CRSn and XBS_PRSn) to be read-only. After set, onlya
RO hardware reset clears it.
0 Both of the slave port's registers are writteable.
1 Both of the slave port's registers are read-only and cannot be written (attempted writes have no effect on the
registers and result in a bus error response).
30–9 Reserved, must be cleared.
8 Arbitration Mode. Selects the arbitration policy for the slave port.
ARB 0 Fixed priority
1 Round robin (rotating) priority
7–6 Reserved, must be cleared.
5–4 Parking control. Determines the slave port's parking control. The low-power park feature results in an overall power
PCTL savings if the slave port is not saturated; however, this forces an extra latency clock when any master tries to access
the slave port while not in use because it is not parked on any master.
00 When no master makes a request, the arbiter parks the slave port on the master port defined by the PARK bit
field.
01 When no master makes a request, the arbiter parks the slave port on the last master to be in control of the slave
port.
10 When no master makes a request, the slave port is not parked on a master and the arbiter drives all outputs to
a constant safe state.
11 Reserved.
3 Reserved, must be cleared.
2–0 Park. Determines which master port the current slave port parks on when no masters are actively making requests
PARK and the PCTL bits are cleared.
000 Park on master port M0 (ColdFire Core)
001 Park on master port M1 (eDMA Controller)
010 Park on master port M2 (FEC)
011 Reserved
100 Park on master port M4 (LCD Controller)
101 Park on master port M5 (USB Host)
110 Park on master port M6 (USB OTG)
111 Reserved
12.5 Functional Description
12.5.1

Arbitration

The crossbar switch supports two arbitration schemes: a simple fixed-priority comparison algorithm and
a simple round-robin fairness algorithm. The arbitration scheme is independently programmable for each
slave port.
12.5.1.1 Fixed-Priority Operation
When operating in fixed-priority mode, each master is assigned a unique priority level in the XBS_PRSn
(priority registers). If two masters request access to a slave port, the master with the highest priority in the
selected priority register gains control over the slave port.
12-6
Table 12-4. XBS_CRSn Field Descriptions
Description
MCF5329 Reference Manual, Rev 3
Freescale Semiconductor