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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...
**HT18 80386SX Single Chip c:Sep91
***Info:...
***Configurations:...
***Features:...
**HT21 386SX/286 Single Chip (20 MHz) c:Aug91...
**HT22 386SX/286 Single Chip (25 MHz) c:Sep91...
**HT25 3-volt Core Logic for 386SX c:Dec92...
**HT35 Single-Chip Peripheral Controller [partial info] ?...
**HTK320 386DX Chip Set c:Sep91...
**HTK340 "Shasta" 486 Chip Set c:Jun92...
**Support Chips:
**HT44 Secondary Cache c:Jun92...
**Other:...
*HMC (Hulon Microelectronics)...
*Logicstar...
*Motorola...
*OPTi...
*PC CHIPS/Amptron/Atrend/ECS/Elpina/etc...
*SIS...
*Symphony...
*TI (Texas Instruments)...
*UMC...
*Unresearched:...
*VIA...
**VT82C680 Apollo P6, Pentium-Pro Chip Set <08/30/96
***Notes:...
***Info:
The VT82C680 Apollo-P6 is a high performance, cost-effective and
energy efficient chip set for the implementation of PCI/ISA desktop
and notebook personal computer systems based on the 64 bit Intel
Pentium-Pro super-scalar processors. The chipset supports multi-
Pentium-Pro configuration with Intel GTL+ driver and receiver inter-
face up to 66 MHz external CPU bus speed. The chipset supports the
Pentium-Pro CPU multi-phase bus protocols for split transactions, four
level deep in-order queue and deferred transactions for optimal CPU
throughput.
The VT82C680 chip set consists of the VT82C685 system controller, the
VT82C687 data buffer and the VT82C586 PCI to ISA bridge. The VT82C680
supports six banks of DRAMs up to 1 GB. The DRAM controller supports
Standard Page Mode DRAM, EDO-DRAM, Burst EDO-DRAM and Synchronous DRAM
in a flexible mixed/match manner. The Burst-EDO and Synchronous DRAM
allows zero wait state bursting between the DRAM and the VT82C687 data
buffers at 66 MHz. The six banks of DRAM allow arbitrary mixture of
1M/2M/4M/8M/16MxN DRAMs with optional bank-by-bank ECC and parity
support. The chipset supports sixteen level (quadwords) of CPU to DRAM
write buffers and sixteen level (quadwords) of DRAM to CPU read
buffers to maximize the CPU bus and DRAM utilization. The peak data
transfer rate for the EDO and Synchronous DRAM (or Burst EDO) DRAMs is
266 MB/s and 532 MB/s, respectively.
The VT82C680 supports 3.3/5v 32 bit PCI bus with 64 bit to 32 bit data
conversion. Sixteen levels (doublewords) of post write buffers are
included to allow for concurrent CPU and PCI operation. Consecutive
CPU addresses are converted into burst PCI cycles with Byte merging
capability for optimal CPU to PCI throughput. For PCI master
operation, sixteen levels (doublewords) of post write buffers and
thirty-two levels (doublewords) of prefetch buffers are included for
concurrent PCI bus and DRAM/cache accesses. The chipset also supports
enhanced PCI bus commands such as Memory-Read-Line,
Memory-Read-Multiple and Memory-Write-Invalid commands to minimize
snoop overhead. In addition, the chipset supports advanced features
such as snoop ahead, snoop filtering, CPU write-back forward to PCI
master and CPU write-back merged with PCI post write buffers to
minimize PCI master read latency and DRAM utilization. The VT82C586
PCI to ISA bridge supports four levels (doublewords) of line buffers,
type F DMA transfers and delay transaction to allow efficient PCI bus
utilization (PCI-2.1 compliant). The VT82C586 also includes integrated
keyboard controller with PS2 mouse support, integrated DS12885 style
real time clock with extended 128 Byte CMOS RAM, integrated master
mode enhanced IDE controller with full scatter and gather capability
and extension to 33 MB/sec UltraDMA-33 transfer rate, integrated USB
interface with root hub and two function ports with built-in physical
layer transceiver, and OnNow/ACPI compliant advanced configuration and
power management interface. A complete main board can be implemented
with only six TTLs.
The VT82C680 is ideal for high performance, high quality, high energy
efficient and high integration desktop and notebook PCI/ISA computer
systems.
***Configurations:...
***Features:...
**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...
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