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**82385 32-bit Cache Controller for 80386 09/29/87
***Notes:...
***Info:
The 82385 Cache Controller is a high performance 32-bit peripheral for
Intel's 80386 Microprocessor. It stores a copy of frequently accessed
code and data from main memory in a zero wait state local cache
memory. The 82385 enables the 80386 to run at its full potential by
reducing the average number of CPU wait states to nearly zero. The
dual bus architecture of the 82385 allows other masters to access
system resources while the 80386 operates locally out of its cache.
In this situation, the 82385's "bus watching" mechanism preserves
cache coherency by monitoring the system bus address lines at no cost
to system or local throughput.
The 82385 is completely software transparent, protecting the integrity
of system software. High performance and board savings are achieved
because the 82385 integrates a cache directory and all cache
management logic on one chip.
1.0 82385 FUNCTIONAL OVERVIEW
Th~ 82385 Cache Controller is a high performance 32-bit peripheral for
Intel's 80386 microprocessor. This chapter provides an overview of
the 82385, and of the basic architecture and operation of an 80386/
82385 system.
1.1 82385 OVERVIEW
The main function of a cache memory system is to provide fast local
storage for frequently accessed code and data. The cache system
intercepts 80386 memory references to see if the required data resides
in the cache. If the data resides in the cache (a hit), it is returned
to the 80386 without incurring wait states. If the data is not cached
(a miss), the reference is forwarded to the system and the data
retrieved from main memory. An efficient cache will yield a high "hit
rate" (the ratio of cache hits to total 80386 accesses), such that the
majority of accesses are serviced with zero wait states. The net
effect is that the wait states incurred in a relatively infrequent
miss are averaged over a large number of accesses, resulting in an
average of nearly zero wait states per access. Since cache hits are
serviced locally, a processor operating out of its local cache has a
much lower "bus utilization" which reduces system bus bandwidth
requirements, making more bandwidth available to other bus masters.
The 82385 Cache Controller integrates a cache directory and all cache
management logic required to support an external 32 Kbyte cache. The
cache directory structure is such that the entire physical address
range of the 80386 (4 Gigabytes) is mapped into the cache. Provision
is made to allow areas of memory to be set aside a non-cacheable. The
user has two cache organization options: direct mapped and 2-way set
associative. Both provide the high hit rates necessary to make a
large, relatively slow main memory array look like a fast, zero wait
state memory to the 80386.
A good hit rate is an essential ingredient of a successful cache
implementation. Hit rate is the measure ,of how efficient a cache is
in maintaining a copy of the most frequently requested code and data.
However, efficiency is not the only factor for performance
consideration. Just as essential are sound cache management
policies. These policies refer to the handling of 80386 writes,
preservation of cache coherency, and ease of system design. The
82385's "posted write" capability allows 80386 memory writes,
including non-cacheable, to run with zero wait states, and the 82385's
"bus watching" mechanism preserves cache coherency with no impact on
system performance. Physically, the 82385 ties directly to the 80386
with virtually no external logic.
***Versions:...
***Features:...
**82385SX 32-bit Cache Controller for 80386SX 01/25/89...
**82395DX High Performance Smart Cache 06/18/90...
**82395SX Smart Cache 12/17/90...
**82396SX Smart Cache 12/17/90...
**82485 Turbo Cache (and 485Turbocache) c90...
**82489DX Advanced Programmable Interrupt Controller 10/12/92...
**82495DX/490DX DX CPU-Cache Chip Set <Sep91...
**82495XP/490XP Cache Controller / Cache RAM (for i860) 06/05/91
***Notes:...
***Info:...
***Features:...
**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...
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**82C802G/GP System/Power Management Controller (cached) c:93
***Notes:...
***Info:...
***Configurations:...
***Features:
[features found only in the 802GP are marked in [] brackets ]
o Processor interface:
- Intel 80486SX, DX, DX2, SLe, DX4, P24T, P24D
- AMD 486SX, DX2, DXL, DXL2, Plus
- Cyrix DX, DX2, M7
- CPU frequencies supported 20, 25, 33, 40 and 50MHz
o Cache interface:
- Direct mapped cache
- Two banks interleaved or single bank non-interleaved
- 64, 128, 256 and 512K cache sizes
- Programmable wait states for L2 cache reads and writes
- 2-1-1-1 read burst and zero wait state write @ 33MHz
- No Valid bit required
[- Supports external single-chip cache modules from thyroid-party ]
[ vendors for high performance at 50MHz ]
- Supports CPUs with L1 write-back support
o DRAM interface:
- Up to 128MB main memory support
- Supports 256KB, 1MB, 4MB, and 16MB single- and double-sided SIMM
modules
- Read page hit timing of 3-2-2-2 at 33MHz
- Supports hidden, slow. and CAS-before-RAS refresh
- Four RAS lines to support four banks of DRAM
[- Eight RAS lines to support four banks of DRAM ]
- Programmable wait states for DRAM reads and writes
[- Programmable memory holes for supporting ISA memory ]
- Enhanced DRAM configuration map
[- Strong drivers on the MA lines (12/24mA) ]
[- Supports asymmetric DRAMs ]
o Power management:
- Support for SMM (System Management Mode) for system power
management implementations
- Programmable power management
[- CPU clock control ]
- Programmable wake-up events through hardware, software, and
external SMI source
- Multiple level GREEN support (NESTED_GREEN)
- STPCLK# protocol support
[- Programmable GREEN event timer ](802G only)
[- Individually programmable peripheral ](802GP only)
o ISA interface:
- 100% IBM PC/AT ISA compatible
[- Programmable edge- or level-trigger interrupts ]
- integrates DMA, timer and interrupt controllers
[- Slew rate control for output drivers ]
- Optional PS/2 style IRQ1 and IRQ12 latching
o VESA VL interface:
- Conforms to the VESA V2.0 specification
- Optional support for up to two VL masters
o Miscellaneous features: (802G only)
- Full support for shadow RAM, write protection, L1/L2
cacheability for video, adapter, and system BIOS
- Enhanced arbitration scheme
- Transparent 8042 emulation for fast CPU reset and GATEA20
generation
o [Miscellaneous features: ](802GP only)
[- Full support for flash, write protection, L1/L2 ]
[ cacheability for video, adapter, and system BIOS ]
[- Provides Micro Channel bridge support ]
[- 10-/16-nit I/O decodes ]
[- Enhanced arbitration scheme ]
o Packaging:
- Higher integration
- Reduced TTL count
- Low-power, high~speed 0.8-micron CMOS technology
- 208-pin PQFP (Plastic Quad Flat Pack)
**82C895 System/Power Management Controller (cached) c:Sep94...
**82C898 System/Power Management Controller (non-cache)c:Nov94...
**
**Support Chips:
**82C601/2 Buffer Devices <Nov94...
**82C822 PCIB (VLB-to-PCI bridge) c:94...
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