Format of PCI Configuration data for Intel 82434LX/NX Cache/DRAM Controller

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Offset

Size

Description

00h

64 BYTEs

header (see #00878) (vendor ID 8086h, device ID 04A3h) (revision numbers: 01h/03h are 82434LX, 1xh are 82434NX) (command register only supports bits 8,6,2,1,0)

40h

16 BYTEs

unused (hard-wired to 00h)

44h

BYTE

??? (AMI BIOS writes 00h)

45h

BYTE

??? (AMI BIOS writes 00h)

50h

BYTE

Host CPU Selection (see #01056)

51h

BYTE

deturbo frequency control register
when deturbo mode is selected (see PORT 0CF9h), the chipset places a hold on the memory bus for a fraction of the time inversely proportional to the value in this register by comparing it against a free-running 8-bit counter counting at 1/8 the CPU clock speed

C0h	=	1/4
80h	=	1/2
40h	=	3/4
20h	=	7/8
etc.

(only bits 7-6 writable, bits 5-0 hardwired to 0)

52h

BYTE

Secondary Cache Control (see #01057)

53h

BYTE

Host Read/Write Buffer Control (see #01058)

54h

BYTE

PCI Read/Write Buffer Control

bits 7-3	:	reserved
bit 2	:	LBXs connected to TRDY#
bit 1	:	enable PCI burst writes
bit 0	:	enable PCI-to-memory posted writes

55h

2 BYTEs

reserved

57h

BYTE

DRAM Control (see #01059)

58h

BYTE

DRAM Timing (see also #01117)

bits 7-2	:	reserved
bit 1	:	(NX only) RAS# Wait State
bit 0	:	CAS# Wait State (one extra wait state before CAS# within burst cycle)

59h

7 BYTEs

Programmable Attribute Map registers 0-6 (see #01118)

60h

8 BYTEs

DRAM Row Boundary registers 0-7 (chip revisions numbered < 10h [LX] only support six rows of DRAM)
each register N indicates the amount of cumulative amount of memory in SIMM banks 0-N, in multiples of 1M; offset 67h (65h on 82434LX's) contains the total amount of memory installed in the system; on the 82434NX, two additional bits are concatenated to each row boundary from the DRAM Row Boundary Extension registers to allow up to 1024M of memory to be specified (though only 512M are supported)

68h

4 BYTEs

(NX only) DRAM Row Boundary Extension registers
each nybble is concatenated with the corresponding DRAM Row Boundary register to form a 12-bit boundary value (of which only the low 10 bits are actually used)

6Ch

DWORD

reserved (hardwired to 00000000h)

70h

BYTE

Error Command (see #01060)

71h

BYTE

Error Status (see #01061)

72h

BYTE

System Management RAM control (see also #01123)

bits 7-6

reserved

bit 5

map SMM-mode memory (64K) into address space when bits 2-0 = 010 (default 3000h:0000h; can be changed by first SMM event)

bit 4

close SMRAM space (allows data accesses to be forwarded to PCI bus while execuding SMM code)

bit 3

lock SMRAM space (can't be cleared by software)

bits 2-0

SMRAM memory address

010	=	Axxxxh
011	=	Bxxxxh

73h

5 BYTEs

reserved

78h

WORD

Memory Space Gap

bit 15	:	enable ISA hole
bits 14-12	:	size of ISA hole in MB (less 1); must be power of 2
bits 11-8	:	reserved
bits 7-4	:	bottom of ISA memory hole in MB (must be multiple of gap size)
bits 3-0	:	reserved

7Ah

2 BYTEs

reserved

7Ch

DWORD

Frame Buffer Range (see #01062)

80h

128 BYTEs

reserved

Note:	The 82434NX is part of the Intel Neptune chipset.
See Also:	#01064,#01083