Samsung S5PC100 User Manual page 314

S5PC100 USER'S MANUAL (REV1.0)
2.3 ROUND-ROBIN (RR) SCHEME
In the RR scheme, you can select the following design time:
•
The number of slots that are used
•
The SI to which they are allocated
•
The order of slots.
There must be at least one slot per connected SI and there can be up to 32 slots. By allocating multiple slots for a
SI, you can allocate access to the slave, on average, in proportion to the number of slots. If the slots are
appropriately ordered, this can also reduce the maximum time before a grant is guaranteed. The SI associated
with a slot can be interrogated from the APB programming interface, but it cannot be changed.
Whenever arbitration is granted to an active SI, the slots are rotated so that the slot currently in the highest priority
position becomes the lowest, and all other slots move to a higher priority but maintain their relative order, as
shown in Figure 3.1-3. This means that if an SI is the highest priority active SI, but is not the highest priority
interface, then it continues to win the arbitration until it becomes the highest priority interface, and then the lowest
priority interface subsequently.
Because the arbitration value is registered, the arbitration decision made in this cycle is used in the next cycle.
This means that if the SI that currently holds the arbitration is still the highest priority active SI in this cycle, wins
the arbitration again regardless of whether or not it is active in the next cycle as shown by the status of M3 in
stages A, B, and C of Figure 3.1-3.
The fixed round robin arbitration scheme is only applied to M0 port of AXI_D1.
Figure 3.1-3 Example Operation of RR Rbitration Scheme
NOTE
BUS CONFIGURATION
3.1-5