RM0319 datasheet(70/368 Pages) STMICROELECTRONICS

70 / 368 page

Multiport DDR controller (MPMC)

RM0319

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Doc ID 022640 Rev 3

Figure 18.

Weighted round-robin priority group structure

Using relative priority concept, the arbitration is skewed in favor of certain ports following

user setting.

Note:

The relative priority parameters have a minimum acceptable value of 1 to prevent port

lockout: A 0 value triggers an error condition.

If the relative priorities are all programmed to the same value within any priority group, the

arbitration will mimic a version of simple round-robin scheme within that specific priority

group. Instead of incrementing as any request is processed, the simple round-robin counter

will only increment to the next port after the ahbX_priorityY_relative_priority number of

requests are processed.

To each port X owning priority level Y, it will be allocated resources corresponding to the

ratio of that port's relative priority (ahbX_priorityY_relative_priority) to the sum of all

requesting port's relative priority values. If a particular port is not requesting, it will be not

included in the sum calculation, i.e. the arbitration will be proportionately split among the

requesting ports.

For instance, let us consider a system with 4 ports where all requests have priority 0. This

system is described in Table 20.

Programmable Register Settings

Priority Group 0

Priority Group 1

Priority Group 2

Priority Group Z

ahb0_priority0_relative_priority

ahb1_priority0_relative_priority

ahb2_priority0_relative_priority

…

abhX_priority0_relative_priority

Priority 0

Priority 2

Priority 1

Priority Z

Commands

ahb0_priority1_relative_priority

…

ahbX_priority1_relative_priority

ahb0_priority2_relative_priority

…

ahbX_priority2_relative_priority

ahb0_priorityZ_relative_priority

…

ahbX_priorityZ_relative_priority

Ports

0-X

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