
File: memsys.fm5, modified 7/24/99
PRELIMINARY INFORMATION
11-1
SDRAM Memory System
Chapter 11
by Eino Jacobs, Chris Nelson, Luis Lucas
11.1
TM1100 MAIN MEMORY OVERVIEW
TM1100 connects to its local memory system with a ded-
terfaces only with SDRAM (or SGRAM with its DSF pin
tied low), and TM1100 is the only master on this bus. For
up to four memory chips, the interface is glueless.
A variety of device types, speeds, and rank1 sizes are
supported, which allows a range of TM1100 systems to
be built.
Table 11-1 summarizes the memory system fea-
tures.
The interface provides all control and data signals with
sufficient drive capacity for a glueless connection to a
133-MHz memory system with up to four memory devic-
es. Note that memory-system speed can be different
from TM1100 core speed; the ratio between the memory
system clock and TM1100 core clock is programmable.
MB memory system with four 2
×1M×8 SDRAM chips
(four devices with 2 banks of one million words, each 8
bits wide) or 16MB with two 4x512Kx32. Larger memo-
ries require a lower memory system clock frequency
(though the TM1100 core clock can be higher), and the
largest memory arrays will require external buffers to in-
crease drive capacity.
11.2
MAIN-MEMORY ADDRESS
APERTURE
TM1100’s local main memory is just one of three aper-
tures into the 4-GB address space of the DSPCPU:
SDRAM (0.5 to 64 MB in size),
MMIO (2 MB in size), and
PCI (any address not in SDRAM or MMIO).
MMIO registers control the positions of the address-
space apertures. The SDRAM aperture begins at the ab-
solute
address
specified
in
the
MMIO
register
DRAM_BASE and extends upward to the address spec-
ified in the DRAM_LIMIT register. If the SDRAM aperture
overlaps the memory hole, the memory hole is ig-
nored.The MMIO aperture begins at the address in
MMIO_BASE, which defaults to 0xEFE00000 after pow-
er-up, and extends upwards two megabytes. (See
Chap-All addresses that fall outside these two apertures are
assumed to be part of the PCI address aperture.
11.3
MEMORY DEVICES SUPPORTED
The devices and organizations supported can be config-
ured as listed in
Table 11-2. All devices must have a
LVTTL, 3.3-V interface.
1.
In this document, the term “rank” is used to refer to a
group of memory devices that are accessed together.
Historically, the term “bank” has been used in this con-
text; to avoid confusion, this document uses “bank” to
refer to on-chip organization (SDRAM devices have two
internal banks) and “rank” to refer to off-chip, system-
level organization.
Table 11-1. Memory System Features
Characteristic
Comments
Data width
32 bits
Number of ranks
Four chip-select signals support up to
four ranks
Memory size
From 512KB to 64MB
Devices
supported
Jedec SGRAM (DSF tied low)
Jedec SDRAM (
×4, ×8, ×16, ×32)
Clock rate
Up to 133 MHz SDRAM speed (program-
mable ratio between TM1100 core clock
and memory system clock)
Bandwidth
532 MB/s (@ 133 MHz)
Glueless interface
Up to four chips @ 133 MHz (e.g., 8
MB memory with 2
×1M×8 SDRAM)
Up to two chips @ 133 MHz (e.g., 16
MB memory with 4x512Kx32 SDRAM)
More chips with slower clock and/or
external buffers
Signal levels
3.3-V LVTTL
Table 11-2. Supported Rank Congurations
Device Size
(Mbit)
Device(s)
Rank Size
22
×64K×16 SDRAM
512 KB
42
×128K×16 SDRAM
1 MB
82
×128K×32 SGRAM
1 MB
16
2
×256K×32 SGRAM
2 MB
2
×512K×16 SDRAM
4 MB
2
×1M×8 SDRAM
8 MB
2
×2M×4 SDRAM
16 MB
64
4x512Kx32 SDRAM
8 MB