Motorola MCF5282 ユーザーズマニュアル

8-12

MOTOROLA

 

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.

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.

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