Microcontroller User's Manual

8-12 MCF5282 User’s Manual MOTOROLA
Internal Bus Arbitration
If no masters are requesting, the arbitration unit must “park”, pointing at one of the masters.
There are two possibilities, park the arbitration unit on the last active master, or park
pointing to the highest priority master. Setting MPARK[PRK_LAST] causes the arbitration
pointer to be parked on the highest priority master. In round-robin mode, programming the
timeout enable and lockout bits MPARK[13,11:8] will have no effect on the arbitration.
8.5.2.2 Fixed Mode
In fixed arbitration the master with highest priority (as specified by the
MPARK[Mn_PRTY] bits) will win the bus. That master will relinquish the bus when all
transfers to that master are complete.
If MPARK[TIMEOUT] is set, a counter will increment for each master for every cycle it is
denied access. When a counter reaches the limit set by MPARK[LCKOUT_TIME], the
arbitration algorithm will be changed to round-robin arbitration mode until all locks are
cleared. The arbitration will then return to fixed mode and the highest priority master will
be granted the bus.
As in round-robin mode, if no masters are requesting, the arbitration pointer will park on
the highest priority master if MPARK[PRK_LAST] is set, or will park on the master which
last requested the bus if cleared.
8.5.3 Bus Master Park Register (MPARK)
The MPARK controls the operation of the system bus arbitration module. The platform bus
master connections are defined as:
• Master 3 (M3): Fast Ethernet Controller
• Master 2 (M2): 4-channel DMA
• Master 1 (M1): Internal Bus Master (not used in normal user operation)
• Master 0 (M0): V2 ColdFire Core
31 26 25 24 23 22 21 20 19 18 17 16
Field — M2_P_EN BCR24BIT M3_PRTY M2_PRTY M0_PRTY M1_PRTY
Reset 0011_0000_1110_0001
R/W R/W
15 14 13 12 11 8 7 0
Field — FIXED TIMEOUT PRKLAST LCKOUT_TIME —
Reset 0000_0000_0000_0000
R/W R/W
Address IPSBAR + 0x01C
Figure 8-7. Default Bus Master Park Register (MPARK)