Problem Solvings With Programmable Round-Robin - Samsung S3C2500B User Manual

S3C2500B

4.6.1 PROBLEM SOLVINGS WITH PROGRAMMABLE ROUND-ROBIN

S3C2500B has a stuff to think about with arbiter operation. This only applies to arbiter with Round-Robin priority.
Assuming all '0's are set for HPRIR register for Round-Robin, HPRIR (all same bus occupancy in Round-Robin),
and only three of six masters are used, the problem arises as follows.
Number
1
2
3
4
5
6
When HPRIR is 0x0 and only GDMA , Ethernet controller 0 and 1 are used, the expected bus occupancy for
each channel is 1/3. However, S3C2500B does not work in that way, instead, GDMA gets 4/6 of the bus
occupancy, Ethernet controller 0 1/6, and Ethernet controller 1 1/6. In short, GDMA is run four times more than
Ethernet controller 0 and 1. This is because S3C2500B is designed to turn the bus occupancy to the next master
when there is non-used master. For instance,
Number 1: GDMA
Number 2: Ethernet controller 0
Number 3: Ethernet controller 1
Number 4: No HDLC 0 -> go to number 5: No HDLC 1 -> go to number 6: No HDLC 2 -> go to number 1: GDMA
Number 5: No HDLC 1 -> go to number 6: No HDLC 2 -> go to number 1: GDMA
Number 6: No HDLC 2 -> go to number 1: GDMA
HPRIR Channel
0 GDMA
0 Ethernet
Controller 0
0 Ethernet
Controller 1
0 Not Used
0 Not Used
0 Not Used
Expected Bus
Occupancy Running Block
1/3
1/3 Ethernet
Controller 0
1/3 Ethernet
Controller 1
0
0
0
SYSTEM CONFIGURATION
Actual Real System
Bus Occupancy
GDMA 1/6
1/6
1/6
GDMA 1/6
GDMA 1/6
GDMA 1/6
4-7