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.

8.5.2.2Fixed 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.

8.5.3Bus 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

Reset

R/W

M2_P_EN BCR24BIT M3_PRTY M2_PRTY M0_PRTY M1_PRTY

0011_0000_1110_0001

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)

 

 

 

 

 

 

 

 

 

 

 

 

8-12

 

 

MCF5282 User’s Manual

MOTOROLA

 

Page 198
Image 198
Motorola MCF5282, MCF5281 user manual Bus Master Park Register Mpark, Fixed Mode, M2PEN BCR24BIT M3PRTY M2PRTY M0PRTY M1PRTY