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**A note on VESA support of 486 chipsets.
Many chipsets state that they support VESA local bus. In some cases
these actually implement VLB somewhat like PCI, where it is entirly
decoupled from the CPU bus. Chipsets that do not state they work with
VLB, may be found on motherboards that contain VLB slots. VLB
is *basically* The 486 CPU pinout in a slot form. Unless these
m/boards contain some additional chips, there VLB implementation is
directly coupled to the CPU.
**Datasheets:...
*_IBM...
*ACC Micro...
*ALD...
*ALi...
*AMD . . . . . . . [no datasheets, some info]...
*Chips & Technologies...
*Contaq . . . . . [no datasheets, some info]...
*Efar Microsystems [no datasheets, some info]...
*ETEQ...
*Faraday...
*Forex . . . . . . [List only, no datasheets found]...
*Intel...
**82395SX Smart Cache 12/17/90
***Notes:...
**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...
**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...
**5571 (Trinity) Pentium PCI/ISA Chipset (75MHz) <12/09/96
***Info:
[no general section in datasheet]
3. Functional Description
3.1 DRAM Controller
3.1.1 DRAM Type
The SiS5571 can support up to 384MBytes (3 banks) of DRAMs and each
bank could be single or double sided 64 bits FP (Fast Page mode) DRAM,
EDO (Extended Data Output) DRAM, and SDRAM (Synchronous DRAM)
DRAM. Half populated bank(32-bit) is also supported.
The installed DRAM type can be 256K, 512k, 1M, 2M, 4M or 16M bit deep
by n bit wide DRAMs, and both symmetrical and asymmetrical type DRAM
are supported. It is also permissible to mix the DRAMs (FP/EDO/SDRAM)
bank by bank and the corresponding DRAM timing will be switched
automatically according to register settings.
3.1.2 DRAM Configuration
The SiS5571 can support single sided or double sided DRAM modules for
each bank. The basic configurations are shown as the following:
3.1.3 Double-sided DRAM [omitted see datasheet]
3.1.4 Single-sided DRAM [omitted see datasheet]
3.1.5 DRAM Scramble Table [omitted see datasheet]
3.1.6 64-bit mapping table [omitted see datasheet]
3.2 DRAM Performance [omitted see datasheet]
3.3 CPU to DRAM Posted Write FIFOs
There is a built-in CPU to Memory posted write buffer with 8 QWord
deep ( CTMFF). All the write access to DRAM will be buffered. For the
CPU read miss / Line fill cycles, the write- back data from the second
level cache will be buffered first, and right after the data had been
posted write into the FIFO, CPU can performs the read operation by the
memory controller starting to read data from DRAMs. The buffered data
are then written to DRAM whenever no any other read DRAM request
comes. With this concurrent write back policy, many wait states are
eliminated. If there comes a bunch of continuous DRAM write cycles,
some ones will be pending if the CTMFF is full.
3.4 32-bit (Half-Populated) DRAM Access
For the read access, there will be either single or burst read cycle
to access the DRAM which depends on the cacheability of the cycle. If
the current DRAM configuration is half-populated bank, then the
SiS5571 will assert 8 consecutive cycles to access DRAM for the burst
cycle. For the single cycle that only accesses DRAM within a DWord,
the SiS5571 will only issue one cycle to access DRAM. For the single
cycle that accesses one Qword or cross DWord boundary, the SiS5571
will issue two consecutive cycles to access DRAM.
3.5 Arbiter
The arbiter is the interface between the DRAM controller and the host
which can access DRAMs. In addition to pass or translate the
information from outside to DRAM controller, arbiter is also
responsible for which master has higher priority to access DRAMs. The
arbiter treats different DRAM access request as DRAM master, and that
makes there be 5 masters which are trying to access DRAMs by sending
their request to the arbiter. After one of them get the grant from the
arbiter, it owns DRAM bus and begins to do memory data transaction.
The masters are: CPU read request, PCI master, Posted write FIFO write
request, and Refresh request. The order of these masters shown above
also stands for their priority to access memory.
3.6 Refresh cycle
The refresh cycle will occur every 15.6 us. It is timed by a counter
of 14Mhz input. The CAS[7:0]# will be asserted at the same time, and
the RAS[5:0]# are asserted sequentially.
3.7 PCI bridge
SiS5571 is able to operate at both asynchronous and synchronous PCI
clocks. Synchronous mode is provided for those synchronous system to
improve the overall system performance. While in the PCI master write
cycles, post-write is always performed. And function of Write Merge
with CPU-to-DRAM post-write buffer is incorporated to eliminate the
penalty of snooping write-back. On the other hand, prefetch is enabled
for master read cycles by default, and such function could be disabled
optionally. And, Direct-Read from CPU-to-DRAM post-write buffer is
implemented to eliminate the overhead of snooping write-back also. In
addition to Write-Merge and Direct-Read, Snoop-Ahead also hides the
overhead of inquiry cycles for master to main memory cycles. These key
functions, Write-Merge, Direct-Read and Snoop-Ahead, achieve the
purpose of zero wait for PCI burst transfer. The post-write and
prefetch buffers are both 16 Double-Word deep FIFOs.
3.8 Snooping Control [omitted see datasheet]
3.9 AHOLD/BOFF# Process and Arbiter Interface [omitted see datasheet]
3.10 Target Initiated Termination [omitted see datasheet]
3.11 DATA Flow [omitted see datasheet]
3.12 PCI Master Read/Write DRAM Cycle [omitted see datasheet]
***Configurations:...
***Features:...
**5581/5582 (Jessie) Pentium PCI/ISA Chipset (75MHz) <04/15/97...
**5591/5592/5595 (David) Pentium PCI A.G.P. Chipset <01/09/98...
**5596/5513 (Genesis) Pentium PCI Chipset <03/26/96...
**5597/5598 (Jedi) Pentium PCI/ISA Chipset <04/15/97...
**530/5595 (Sinbad) Host, PCI, 3D Graphics & Mem. Ctrl.<11/10/98...
**540 (Spartan) Super7 2D/3D Ultra-AGP Single C.S.<11/30/99...
**55x SoC (System-on-chip) <03/14/02...
**
**Support chips:
**85C206 Integrated Peripheral Controller [no datasheet] ?...
**5595 Pentium PCI System I/O <12/24/97...
**950 LPC I/O <07/16/99...
**Other:...
**PII/III/Pro...
**Athlon etc...
*Symphony...
*TI (Texas Instruments)...
*UMC...
*Unresearched:...
*VIA...
**VT82C598MVP Apollo MVP3,Single-Chip 66/75/83/100MHz & AGP <09/22/97
***Notes:...
***Info:...
***Configurations:...
***Features:...
**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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