Samsung S5PC110 Manual page 480

S5PC110_UM
1.1.1.2 Round-robin (RR) Scheme
In the RR scheme, you can select the following design time:
• Number of used slots
• SI to which these slots are allocated
• Order of slots
There must be at least one slot per connected SI and 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 by APB programming interface, but it cannot be changed.
Whenever arbitration is granted to an active SI, the slots are rotated so that the slot 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
1-2. This means that if an SI is the highest priority active SI, but is not the highest priority interface, then it
Figure
continues to win the arbitration until it becomes the highest priority interface, and then the lowest priority interface
subsequently.
Since the arbitration value is registered, the arbitration decision made in this cycle is used in the next cycle. This
means that if SI (that currently holds the arbitration) has the highest priority active SI in this cycle, it 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 in
Figure 1-2.
Figure 1-2 Example Operation of RR Arbitration Scheme
1 BUS CONFIGURATION
1-4