Transaction0
Time t
Transaction1
Transaction2
Transaction3
Transaction5
Transaction6
Arbitration decision on a transaction boundary:
Which group has the priority?
Duration of a transaction:
How long to track the transaction?
(it depends on the granularity settings)
sdrc-024
Transaction4
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Figure 10-67. Arbitration Granularity Versus Arbitration Decision
10.2.6.2.2 Arbitration Decision
The SMS module controls arbitration. Requests from initiators for access to the external SDRAM are
collected into several independent FIFO queues, and each queue is assigned to a class. Priority is then
assigned to groups and classes; this defines the next request to be serviced.
10.2.6.2.2.1 Burst-Complete Mechanism
The burst-complete mechanism applies granularity to the arbitration scheme. Access cannot be granted to
a group within a class until a complete burst has been stored in the FIFO.
Example:
There is no ongoing transaction on Class 0. The initiator requests a 4 * 64-bit burst on Group 3 of Class 2
(
[27] BURST-COMPLETE = 0x1). Only 2 * 64-bit requests are stored in the
FIFO.
The mode of operation is:
•
Wait for the last 2 * 64-bit request to be stored in the FIFO.
•
Arbitration is requested once all requests of a burst have been received.
•
After the 4 * 64-bit burst is complete, the transaction occurs.
•
The arbitration choice mechanism resumes:
–
Were there any incoming requests during the last transaction?
–
What is the next request to be serviced/granted?
2286
Memory Subsystem
SWPU177N – December 2009 – Revised November 2010
Copyright © 2009–2010, Texas Instruments Incorporated