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**82495DX/490DX DX CPU-Cache Chip Set <Sep91
***Notes:...
***Info:
The 50 MHz Intel486 DX CPU-Cache Chip Set provides a high performance
solution for servers and high-end desktop systems. This binary
compatible solution has been optimized to provide 50 MHz, zero wait
state performance. The CPU-Cache chip set combines the 50 MHz Intel486
Microprocessor with the 82495DX/82490DX cache subsystem. It delivers
integer performance of 41 V1.1 Dhrystone MlPs and a SPEC integer
rating of 27.9. The cache subsystem features the 82495DX Cache
Controller and the 82490DX Dual Ported Data RAM. Dual ported buffers
and registers of the 82490DX allow the 82495DX Cache Controller to
concurrently handle CPU bus, memory bus, and internal cache operations
for maximum performance.
The CPU-Cache Chip Set offers many features that are ideal for multi-
processor based systems. The Write-Back feature provides efficient
memory bus utilization by reducing bus traffic through eliminating
unnecessary writes to main memory. The CPU-Cache chip set also
supports MESI protocol and monitors the memory bus to guarantee cache
coherency.
The 50 MHz Intel486 DX CPU and 82495DX/82490DX Cache subsystem are
produced on Intel's latest CHMOS V process which features submicron
technology and triple layer metal.
3.0 ARCHITECTURAL OVERVIEW
3.1 Introduction
The Intel486 CPU-cache chip set provides a tightly coupled processing
engine based on the Intel486 microprocessor and a cache subsystem
comprised of the 82495DX cache controller and multiple 82490DX cache
components. Figure 3.1 [see datasheet] diagrams the basic config-
uration.
The cache subsystem provides a gateway between the CPU and the memory
bus. All CPU accesses that can be serviced locally are transparent to
the memory bus and serve to avoid bus traffic. As a result, the cache
chip set reduces memory bus bandwidth to both increase Intel486
processor performance and support efficient multiprocessor systems.
The cache subsystem also decouples the CPU from the memory bus to
provide zero-wait-state operation at high clock frequencies while
allowing relatively slow and inexpensive memories.
The CPU-cache chip set prevents latency and bandwidth bottlenecks
across a variety of uniprocessor and multiprocessor designs. The
processor’s on-chip cache supports a very wide CPU data bus and
high-speed data movement. The second-level cache greatly extends the
capabilities of the on-chip cache resources, enabling a larger portion
of memory cycles to be satisfied independently of the memory bus.
3.2 CPU-Cache Chip Set Description
The chip set is comprised of three functional blocks:
3.2.1 CPU
The chip set includes a special version of the Intel486DX micropro-
cessor at 50 MHz. The Intel486DX Microprocessor Data Sheet provides
complete component specifications.
3.2.2 CACHE CONTROLLER
The 82495DX cache controller is the main control element for the chip
set. providing tags and line states. and determining cache hits and
misses. The 82495DX executes all CPU bus requests and coordinates all
main memory accesses with the memory bus controller (MBC).
The 82495DX controls the data paths of the 82490DX cache components
for cache hits and misses and furnishes the CPU with needed data. The
controller dynamically adds wait states as needed using the most
recently used (MRU) prediction algorithm.
The 82495DX also performs memory bus snoop operations in shared memory
systems and drives the cycle address and other attributes during
memory bus accesses. Figure 3.2 [see datasheet] diagrams the 82495DX.
3.2.3 CACHE SRAM
Multiple 82490DX cache components provide the cache SRAM and data
path. Each component includes the latches, muxes and logic needed to
work in lock step with the 82495DX to efficiently serve both hit and
miss accesses. The 82490DX components take full advantage of VLSI
silicon flexibility to exceed the capabilities of discrete
implementations. The 82490DX components support zero-wait-state hit
accesses and concurrent CPU and memory bus accesses, and they
replicate MRU bits for autonomous way prediction. During memory bus
cycles. the 82490DX components act as a gateway between CPU and memory
buses. Figure 3.3 [see datasheet] diagrams an 82490DX cache component.
3.3 Secondary Cache Features
The 82495DX cache controller and 82490DX cache components provide a
unified, software transparent secondary data and instruction cache.
The cache enables a highspeed processor core that provides efficient
performance even when paired with a significantly slower memory bus.
The secondary cache interprets CPU bus cycles and can service most
memory read and write cycles without accessing main memory. I/O and
other special cycles are passed directly to the memory bus. The cache
has a dual-port structure that permits concurrent CPU and memory bus
operation.
The 82495DX cache controller contains the 8K tag entries and logic
needed to support a cache as large as 256K. Combinations of between 4
and 9 82490DX cache SRAMs are used to create caches ranging from 128K
to 256K, with or without data parity.
The MBC provides logic needed to interface the CPU, 82495DX and
82490DX to the memory bus. Because the MBC also affects system
performance. its design can be the basis of product differentiation.
***Configurations:...
***Features:...
**82495XP/490XP Cache Controller / Cache RAM (for i860) 06/05/91...
**82496/491 Cache Controller / Cache RAM (for P5 Pentium) 03/22/93...
**82497/492 Cache Controller / Cache RAM (for P54 Pentium) <Nov94...
**82498/493 Cache Controller / Cache RAM (for P54 Pentium) <Nov94...
**
**Later chipsets (basic spec):
**440 series:...
**450NX (?) 06/29/98:...
**????? (Profusion) c:99...
**800 series...
*Headland/G2...
*HMC (Hulon Microelectronics)...
*Logicstar...
*Motorola...
*OPTi...
*PC CHIPS/Amptron/Atrend/ECS/Elpina/etc...
*SIS...
*Symphony...
**SL82C470 'Mozart' 486/386 EISA chipset c:Dec91
***Info:
The SL82C470 chip set provides a very high performance. highly inte-
grated and cost-effective implementation for personal computer systems
based on the standard EISA bus. It supports both 386DX and 486DX/SX
CPUs over the entire performance range, from 20Mhz to 50Mhz. The chip
set can operate in either "conventional" or "concurrent" config-
uration. Under the conventional configuration, the cache subsystem is
dedicated to bus snooping when a DMA or master device becomes active.
Under the concurrent configuration, the CPU-cache operation continues
while bus snooping is performed for the DMA or master device to
explore maximum concurrency between the CPU and the EISA bus. Only
ten TTLs are required for a complete motherboard design under the
conventional configuration in addition to the chip set and memory
devices. Five additional TTLs are required for the concurrent
configuration. A complete EISA system of either configuration can be
easily implemented on a baby AT sized motherboard.
The SL82C470 chip set consists of three 160-pin PQFP devices: the
SL82C471 integrated cache/DRAM controller, the SL82C472 EISA bus
controller and the SL82C473 DMA controller.
SL820471 Cache/DRAM Controller
The SL82C47l Cache/DRAM controller controls the cache and DRAM
accesses from the CPU, EISA/ISA masters and DMA devices. The chip
adapts a write-back cache scheme to minimize the interference between
the CPU-cache and DMA/master during their concurrent operations. The
cache size ranges from 64KB to 1MB with advanced features such as
2-1-1-1 burst line fill. Snoop-filtering, local bus support and
programmable non-cacheable and write-protected regions. The page mode
DRAM controller supports 1 to 4 banks of DRAMS up to 256MB. A mixture
of 256KB, 1MB. 4MB and 16MB DRAMs is supported. The video and system
BIOS can be shadowed or cached independently. The cache-DRAM
subsystem allows zero wait state burst mode DMA transfers to take full
advantage of the high bandwidth of the EISA bus.
The DRAM data bus can either be connected directly to the CPU local
bus or be buffered externally, The control signals for the external
buffers are generated by the SL82C471.
SL82C472 EISA Bus Controller
The SL82C472 EISA bus controller translates bus control signals
between the CPU, EISA/ISA and DMA masters and slaves. The chip also
includes buffers and byte/word swap logic between the CPU (or DRAM)
and the EISA bus. The bus conversion and data alignment are performed
automatically.
The SL82C472 includes two 8259 interrupt controllers and four 8254
timer channels modified for 100% EISA compatibility. The chip also
includes parity generation and check logic and NMI and timeout logic.
SL82C473 EISA DMA Controller
The SL82C473 DMA controller implements seven EISA DMA channels. the
system arbiter and the co-processor interface logic. The DMA control-
ler supports compatible type A, type B and type C (burst) mode
operations with the buffer chaining capability. The multilevel
rotating priority arbitration with fail-safe timeout is implemented
for the system arbiter. Six sets of slot-specific master handshake
signals (MACK and MREQ) are provided directly without any external
components.
The address latches and buffers for the EISA bus are also included in
the SL82C473.
***Configurations:...
***Features:...
**SL82C490 'Wagner' 486? [no datasheet] ?...
**SL82C550 'Rossini' Pentium [no datasheet] c:95...
**
**Support Chips:
**SL82C365 Cache Controller (for 386DX/SX) c:91...
**SL82C465 Cache Controller (for 486/386DX/SX) c:91...
*TI (Texas Instruments)...
*UMC...
*Unresearched:...
*VIA...
**VT82C597/AT Apollo VP3, Single-Chip for Pentium with AGP <10/03/97
***Info:...
***Configurations:...
***Features:...
**VT82C598MVP Apollo MVP3,Single-Chip 66/75/83/100MHz & AGP <09/22/97...
**VT8501 Apollo MVP4,Single-Chip 66-100MHz & AGP <11/04/98...
**VT82C680 Apollo P6, Pentium-Pro Chip Set <08/30/96...
**Support chips:
**VT82C505 Pentium/486 VL to PCI Bridge <05/30/94...
**VT82C586/A/B PCI Integrated Peripheral Controller <10/13/96...
**VT82C596/A Mobile PCI Integrated Peripheral Controller <11/05/97...
**VT82C686A/B PCI Super-I/O Integrated Peripheral Ctrl. <02/10/98...
**Later P-Pro/II/III/Celeron...
**Later AMD...
**Other...
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