RM0319 datasheet(69/368 Pages) STMICROELECTRONICS

69 / 368 page

RM0319

Multiport DDR controller (MPMC)

Doc ID 022640 Rev 3

69/368

Understanding port priority

For AHB ports, the priority is associated with a port and each port has separate priority

parameter for READ and WRITE operations. These values are stored into the

programmable parameters ahbX_r_priority and ahbX_w_priority (where X is the port

number) at startup. Internally, the ports are organized into priority groups based on their

priority setting.

The priority value is also used by the placement logic inside the core when filling the

command queue, with “0” meaning highest priority and “7” as lowest priority.

Even if the user is allowed to set a “0” priority level, it would be better to avoid this specific

value so the placement queue can reach this level by aging.

Understanding relative priority

Inside each priority group, the relative priority is used to set arbitration. The MPMC contains

8 identical priority groups with control logic selecting among the requests from all ports at

that given priority level. The relative priority parameters ahbX_priorityY_relative_priority

(where X being the port number and Y the priority group) “weight” the ports for each level

and determine how the priority group will be arbitrated.

Figure 18 shows this type of arbitration system.

YYYes

None

YYNo

Table 19.

Round-Robin operation example

Cycle

Port addressed

by an arbitration

counter

Port requesting

Command

queue full?

Winner of

arbitration

Value of counter

at the next cycle

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