Texas Instruments OMAP36 Series, Technical Reference Manual, Page: 2290 / 3738

Group 0
Group 1 Group 2 Group 3
Group 7 Group 6
Class 1
Class 0
.......
Class 2
Request for transaction on group 1 occurs
during transactions on group 0.
Class 1 - group 0 is granted for three consecutive transactions.
To service the other requests (pending or new incoming), wait
until completion of these three transactions.
Request for transaction on class 0 occurs during
transactions on class 1 - group 0.
Requests were present on
group 0 and group 3.
An arbitration decision occurs.
Class 1 was granted the access.
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Figure 10-71. Example of EXTENDEDGRANT Mechanism
10.2.6.2.3.3 Number of Service Mechanism.
The SMS_CLASS_ROTATIONm [4:0] NOFSERVICES field defines the number of consecutive
transactions (from 1 to 31) the VRFB is granted. For more information on LRU policy and Number of
Service, refer to
Section 10.2.4.1.3 .
10.2.6.2.4 How these Mechanisms Interact
As described in the previous sections, the arbitration within the SMS module is based on several
mechanisms giving even more importance to the arbitration. Wen we need to grant the access on a
transaction boundary, we recall that the question we have to answer is: What will be the next request to
be serviced, and for how long?
Thus, the two important concepts regarding the SMS mode of operation are:
•
The arbitration decision: we choose the next request to be serviced and so we grant it the access to
the external memory.
• The arbitration granularity: depending on the mechanism used, we define the boundary of the
transaction: how long do we keep the grant?
Figure 10-72 describes the decision happening between classes.
Figure 10-73 explains the priority between groups within Class 1.
So far, the arbitration decision has taken place at class boundaries and within a class containing two
groups.
Figure 10-74 recalls the generic way to service and therefore prioritize the requests within a class.
Finally, Figure 10-75 recalls mechanisms used to define the boundary of the transaction being serviced
(how long do we keep the grant?).
2290 Memory Subsystem SWPU177N – December 2009 – Revised November 2010
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