Chapter 10 Memory Subsystem.pdf
Chapter 10 Memory Subsystem.pdf
Chapter 10 Memory Subsystem.pdf
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Transaction0<br />
Duration of a transaction:<br />
How long to track the transaction?<br />
(it depends on the granularity settings)<br />
Arbitration decision on a transaction boundary:<br />
Which group has the priority?<br />
Public Version<br />
SDRAM Controller (SDRC) <strong>Subsystem</strong> www.ti.com<br />
<strong>10</strong>.2.6.2.2 Arbitration Decision<br />
Figure <strong>10</strong>-67. Arbitration Granularity Versus Arbitration Decision<br />
Transaction4<br />
Transaction1 Transaction2 Transaction3 Transaction5 Transaction6<br />
The SMS module controls arbitration. Requests from initiators for access to the external SDRAM are<br />
collected into several independent FIFO queues, and each queue is assigned to a class. Priority is then<br />
assigned to groups and classes; this defines the next request to be serviced.<br />
<strong>10</strong>.2.6.2.2.1 Burst-Complete Mechanism<br />
The burst-complete mechanism applies granularity to the arbitration scheme. Access cannot be granted to<br />
a group within a class until a complete burst has been stored in the FIFO.<br />
Example:<br />
There is no ongoing transaction on Class 0. The initiator requests a 4 * 64-bit burst on Group 3 of Class 2<br />
(SMS_CLASS_ARBITER2[27] BURST-COMPLETE = 0x1). Only 2 * 64-bit requests are stored in the<br />
FIFO.<br />
The mode of operation is:<br />
• Wait for the last 2 * 64-bit request to be stored in the FIFO.<br />
• Arbitration is requested once all requests of a burst have been received.<br />
• After the 4 * 64-bit burst is complete, the transaction occurs.<br />
• The arbitration choice mechanism resumes:<br />
– Were there any incoming requests during the last transaction?<br />
– What is the next request to be serviced/granted?<br />
2268 <strong>Memory</strong> <strong>Subsystem</strong> SPRUGN4L–May 20<strong>10</strong>–Revised June 2011<br />
Copyright © 20<strong>10</strong>–2011, Texas Instruments Incorporated<br />
Time t<br />
sdrc-024