External Memory Controller (EMC)
Symphony DSP56724/DSP56725 Multi-Core Audio Processors, Rev. 0
Freescale Semiconductor
21-39
21.4
Functional Description
The EMC allows the implementation of memory systems with specific timing requirements. In this
section, the SDRAM, GPCM, and UPM machines will be described using diagrams and waveforms.
Unless it is noted otherwise, the waveforms shown are observed in the de-skew PLL enable mode.
•
To achieve high performance through a multiplexed address and data bus, the SDRAM machine
provides an interface to synchronous DRAMs using bank interleaving and back-to-back page
mode. An internal phase-locked loop (PLL) for bus clock generation ensures improved data set-up
margins for board designs.
•
The GPCM machine provides interfacing for simpler, lower-performance memories and
memory-mapped devices. The GPCM has inherently lower performance because it does not
support bursting. For this reason, GPCM-controlled banks are used primarily for boot-loading and
access to low-performance memory-mapped peripherals.
•
The UPM machine supports refresh timers, address multiplexing of the external bus, and the
generation of programmable control signals for row address and column address strobes, to allow
for a minimal glue logic interface to DRAMs, burstable SRAMs, and almost any other type of
peripheral. The UPM can be used to generate flexible, user-defined timing patterns for control
signals that govern a memory device. These patterns define how the external control signals behave
Table 21-63. Clock Ratio Register Low Part
LCRRL
23
22
21
20
19
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
X:0xFF_FE6A
R
W
R
CLKDIV
W
Reset
0x00_0000
Table 21-64. LCRRL Field Descriptions
Bits
Name
Description
23–4
—
Reserved
3–0
CLKDIV
System (input) clock divider. Sets the frequency ratio between the (input) system clock and the
memory bus clock. Only the values shown in the list below are allowed.
0000 Reserved
0001 Reserved
0010 2
0011 Reserved
0100 4
0101 Reserved
0110 Reserved
0111 Reserved
1000 8
1001–1111 Reserved
Содержание Symphony DSP56724
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