Chapter 10 Memory Subsystem.pdf

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www.ti.com SDRAM Controller (SDRC) Subsystem
appropriate.
– When performing burst accesses with 90° or 270° rotation views, the burst is split on the memory
side, adding latency.
For a burst access with 90° rotation, split the data of the burst on the write side (not the read side):
• Write in 270°° and read in 0°.
10.2.6.2 SMS Mode of Operation
10.2.6.2.1 SDRAM Memory Scheduler and Arbitration Policy
The SDRAM memory scheduler improves access to external memory by:
• Optimizing SDRAM bandwidth
• Prioritizing requests to external memory
This mechanism relies on a complex arbitration policy that employs specific terminology:
• Group: a FIFO queue of requests from initiators
• Class: A collection of groups
• Transaction: A full burst request
• Arbitration grant: Authorization of a service requested by an initiator
The arbitration policy operates on two interdependent mechanisms:
• The arbitration decision, which establishes priority for processing requests. The question: Which
request is processed next? occurs on a transaction boundary.
• Arbitration granularity, which determines the length of an arbitration grant. The question: How long to
keep the grant? defines the boundary of the arbitration decision point in time.
Figure 10-67 shows the link between these two concepts. On a transaction boundary, the questions: What
request is serviced next, and for how long? merge the two mechanisms. The mechanisms for specifying
the granularity of requests also influence the boundary of a transaction.
SPRUGN4L–May 2010–Revised June 2011 Memory Subsystem
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