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On-Card Memory Configuration: On-Card SDRAM
PmPPC7448 User’s Manual 10006757-02
4-2
If booting from user Flash, the MV64460 controller initially maps one megabyte addressing
of Flash memory (beginning at FF80,0000
16
) at the top of the address space. When an 8-bit
Flash device is installed in the PLCC socket, it always appears at F800,0000
16
(and is mir-
rored at FF80,0000
16
when the socket is the boot device).
Caution: When removing socketed PLCC devices, always use an extraction tool designed specifically
for that task. Otherwise, you risk damaging the PLCC device.
Since the 16-bit Flash device is soldered, an 8-bit ROM could be used to bootstrap the pro-
cessor and execute a routine that programs the soldered Flash from a serial port, Ethernet,
or through the PCI interface.
ON-CARD SDRAM
The PmPPC7448 supports 256 megabyte, 512 megabyte, 1 gigabyte, and 2 gigabyte con-
figurations of 72-bit wide SDRAM. This interface implements eight additional bits to permit
the use of error-correcting code (ECC).
A low profile, small-outline, dual inline memory module (SO-DIMM) is installed to reduce
board density and routing constraints. A serial EEPROM on the module provides the serial
presence detects (SPD). On-card SDRAM occupies physical addresses from 0000,0000
16
to
7FFF,FFFF
16
. The SDRAM is controlled by the MV64460 DRAM controller, which may be pro-
grammed for most memory sizes and speeds, various block sizes, and write protection.
In addition to the basic SDRAM control functions, the MV64460 chip provides several addi-
tional DRAM-related functions and contains the following performance enhancing fea-
tures:
• Supports page mode—minimizing SDRAM cycles on multiple transactions to the same
SDRAM page and can be configured to support up to 16 simultaneously opened pages.
• Supports error-correcting code (ECC) and read-modify-write (RMW) in the case of
partial writes (smaller than 64-bit) to DRAM.
• ECC provides single bit correction and two bits detection.
NVRAM ALLOCATION
The PmPPC7448 uses an eight kilobyte SROM attached to the MV64460 bridge for storing
non-volatile information such as board, monitor, and operating system configurations, as
well as information specific to user application. All Emerson-specific data is stored in the
upper two kilobytes of the device. The remainder of the device is available for user applica-
tion.
Table 4-3 defines the organization of data within the SROM.
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