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UM10503
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© NXP B.V. 2015. All rights reserved.
User manual
Rev. 2.1 — 10 December 2015
620 of 1441
NXP Semiconductors
UM10503
Chapter 23: LPC43xx/LPC43Sxx External Memory Controller (EMC)
The EMC dynamic memory interface requires that all EMC_CLK signals are selected on
the CLKn pins for 16-bit memory and for 32-bit memory.
For static memory larger delays are defined by in steps of one EMC clock cycle by the
STATICWAIT registers (see
to
).
23.8.4 Data buffers
The AHB interface reads and writes via buffers to improve memory bandwidth and reduce
transaction latency. The EMC contains four 16-word buffers. The buffers can be used as
read buffers, write buffers, or a combination of both. The buffers are allocated
automatically.
The buffers must be disabled during SDRAM initialization. The buffers must be enabled
during normal operation.
The buffers can be enabled or disabled for static memory using the StaticConfig
Registers.
23.8.4.1 Write buffers
Write buffers are used to:
•
Merge write transactions so that the number of external transactions are minimized.
Buffer data until the EMC can complete the write transaction, improving AHB write
latency.
Convert all dynamic memory write transactions into quadword bursts on the external
memory interface. This enhances transfer efficiency for dynamic memory.
•
Reduce external memory traffic. This improves memory bandwidth and reduces
power consumption.
Write buffer operation:
•
If the buffers are enabled, an AHB write operation writes into the Least Recently Used
(LRU) buffer, if empty.
If the LRU buffer is not empty, the contents of the buffer are flushed to memory to
make space for the AHB write data.
•
If a buffer contains write data it is marked as dirty, and its contents are written to
memory before the buffer can be reallocated.
The write buffers are flushed whenever:
•
The memory controller state machine is not busy performing accesses to external
memory.
The memory controller state machine is not busy performing accesses to external
memory, and an AHB interface is writing to a different buffer.
Note: For dynamic memory, the smallest buffer flush is a quadword of data. For static
memory, the smallest buffer flush is a byte of data.
23.8.4.2 Read buffers
Read buffers are used to: