Problem Solvings With Programmable Round-Robin - Samsung S3C2501X User Manual

S3C2501X

4.6.1 PROBLEM SOLVINGS WITH PROGRAMMABLE ROUND-ROBIN

S3C2501X 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 HPRIR
1 0
2 0
3 0
4 0
5 0
6 0
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, S3C2501X does not work 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 S3C2501X 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: Reserved Master 0 → go to number 5: Reserved Master 1 → go to number 6: Reserved Master 2 →
go to number 1: GDMA
Number 5: Reserved Master 1 → go to number 6: Reserved Master 2 → go to number 1: GDMA
Number 6: Reserved Master 2 → go to number 1: GDMA
Channel
GDMA
Ethernet Controller 0
Ethernet Controller 1
Reserved Master 0
Reserved Master 1
Reserved Master 2
Expected Bus Actual Running
Occupancy
1/3
1/3 Ethernet Controller 0
1/3 Ethernet Controller 1
0
0
0
SYSTEM CONFIGURATION
Real System
Block Bus Occupancy
GDMA
GDMA
GDMA
GDMA
1/6
1/6
1/6
1/6
1/6
1/6
4-7