Philips Semiconductors
SDRAM Memory System
PRELIMINARY SPECIFICATION
12-3
terface must be lowered to account for extra propagation
delay due to the excessive loading on the interface sig-
nals (see
Section 12.13,
“
Output Driver Capacity
”
).
The following rules apply to memory rank design:
All devices in a rank must be of the same type.
All ranks must be a power of two in size.
All ranks must be of equal size.
Table 12-4
lists some examples of 32-bit memory sys-
tem designs.
Refer to the TM-1100 Databook for smaller memory con-
figurations.
Note:
Some of these configurations may not be economi-
cally attractive due to the price premium.
‘
Max. MHz
’
refers to the memory interface/SDRAM
speed, not the PNX1300 core operating frequency.
The maximum MHz also depends on the device
being used, i.e. PNX1300, PNX1311 or PNX1302.
Refer to
Section 1.9.7.10 on page 1-18
for maximum
operating speeds.
Table 12-4
lists some example of 32-bit memory system
designs.
12.6
MEMORY SYSTEM PROGRAMMING
Memory system parameters are determined by the con-
tents of two configuration registers, MM_CONFIG and
PLL_RATIOS.
Table 12-6
describes the function of
these registers, and
Figure 12-2
shows their formats.
To ensure compatibility with future devices, any unde-
fined MMIO bits should be ignored when read.
MM_CONFIG and PLL_RATIOS are loaded from the
boot EEPROM, as described in
Section 13.4,
“
Detailed
EEPROM Contents.
”
During this boot process, the mem-
ory interface is held in reset state. After the memory in-
terface is released from reset, the contents of these reg-
isters cannot be altered.
These registers are visible in MMIO space. They can be
read, but writes have no effect.
12.6.1
MM_CONFIG Register
The MM_CONFIG register tells the memory interface
how to use the local DRAM memory. The fields in this
register tell the interface the rank size and the refresh
rate of the memory.
Table 12-8
summarizes the field
functions.
REFRESH (Refresh interval).
The 16-bit REFRESH
field specifies the number of memory-system clock cy-
cles between refresh operations. The default value of
this field is 1000 (0x03E8). See
Section 12.11,
“
Refresh,
”
for more information.
BW (Bus Width).
If set to
‘
0
’
then the memory interface
data bus width is 32 bits. If set to
‘
1
’
then the memory in-
terface data bus width is 16 bits.
SIZE (Rank size).
The 3-bit SIZE field specifies the size
of each rank of DRAM. Each rank must be the size spec-
ified by SIZE. The default is a rank size of 4MB. Refer to
Table 12-7
for the interpretation of this field.
Table 12-4.
Examples of 32-bit Memory Configurations
Size
(MB)
Ranks
Rank Configurations
Max.
MHz
Peak
MB/s
8
1
2
four 2
×
1M
×
8 SDRAM
two 2
×
512K
×
16 SDRAM
two 2
×
512K
×
16 SDRAM
one 4
×
512K
×
two 4
×
1M
×
16 SDRAM
one 4
×
1M
×
32 SDRAM
one 4
×
512K
×
32 SDRAM
one 4
×
512K
×
32 SDRAM
one 4
×
512K
×
32 SDRAM
one 4
×
512K
×
32 SDRAM
one 4
×
512K
×
32 SDRAM
two 4
×
2M
×
16 SDRAM
166
166
664
664
1
1
1
2
183
183
183
183
732
732
732
732
16
24
3
166
664
32
1
1
1
1
2
1. However MM_CONFIG.SIZE may be 16 MB (i.e.
6). Refer to
Figure 12-10
and
Figure 12-11
for
the two possible connection details.
2. However MM_CONFIG.SIZE is 32 MB (i.e. 7).
183
732
four 4
×
2M
×
8 SDRAM
166
664
two 4
×
1M
×
16 SDRAM
two 4
×
1M
×
16 SDRAM
one 4
×
1M
×
32 SDRAM
one 4
×
1M
×
32 SDRAM
one 4
×
512K
×
32 SDRAM
one 4
×
512K
×
32 SDRAM
one 4
×
512K
×
32 SDRAM
one 4
×
512K
×
32 SDRAM
one 4
×
1M
×
32 SDRAM
one 4
×
1M
×
32 SDRAM
one 4
×
1M
×
32 SDRAM
two 4
×
4M
×
16 SDRAM
166
664
2
183
732
4
166
664
48
3
166
664
64
1
2
4
183
732
one 4
×
1M
×
32 SDRAM
one 4
×
1M
×
32 SDRAM
one 4
×
1M
×
32 SDRAM
one 4
×
1M
×
32 SDRAM
166
664
Table 12-5.
Supported 16-bit Memory Configurations
Size
(MB)
Ranks
Rank Configurations
Max.
MHz
Peak
MB/s
8
1
1
one 4
×
1M
×
16 SDRAM
one 4
×
2M
×
16 SDRAM
183
183
732
732
16
1
32
2
1.
2.
However MM_CONFIG.SIZE is set to 8 MB (i.e. 5)
However MM_CONFIG.SIZE is set to 8 MB (i.e. 5)
1
one 4
×
4M
×
16 SDRAM
183
732