Samsung S5PC110 Manual page 481

S5PC110_UM
1.1.1.3 Least Recently Granted Scheme
In the Least Recently Granted (LRG) scheme, each connected SI has a single slot associated with it, but each
interface also has a priority value. This priority value, whose post-reset value can be configured at design time,
programmed, or interrogated through the APB programming interface, can make the arbiter behave as:
• Pure LRG scheme
• Fixed priority encoder
• Combination of the two
All masters with the same priority form a priority group. As a result of arbitration, a master can move within its
priority group but cannot leave its group, and no new masters can join the group.
Arbitration is granted to the highest priority group from which a member is trying to win access and within that
group to the highest master at that time. When master wins arbitration, it is relegated to the bottom of its group to
ensure that it does not prevent other masters in its group from accessing the slave.
If you configure all master priorities to different levels, the arbiter implements a fixed priority scheme. This occurs
because in this case, each master is in a group of its own, and therefore, masters maintain their ordering.
If all master priorities are the same, then an LRG scheme is implemented. The reason all master priorities behave
as LRG is because the process of relegating the master that was last granted access to the bottom of its group
results in the masters being ordered from the LRG master at the top to the Most Recently Granted (MRG) at the
bottom.
The LRG and fixed priority modes concurrently exist when the master priority values are set with a combination of
identical and unique values. You can mix priority groups that contain one member with priority groups that contain
more than one member in an arbitrary manner. The arbiter places no restriction on the number of groups or their
membership.
shows the movement of masters within their priority groups.
Figure 1-3
Figure 1-3 Example Operation of LRG Arbitration Scheme
1 BUS CONFIGURATION
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