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Format of PCI Configuration data for Intel 82425EX PSC

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Offset Size Description

00h

64 BYTEs

header (see #00878) (vendor ID 8086h, device ID 0486h)

40h

BYTE

PCI control register (see #01084)

41h

3 BYTEs

???

44h

BYTE

host device control register (see #01085)

45h

3 BYTEs

???

48h

WORD

PCI local-bus IDE control register (see #01086)

4Ah

2 BYTEs

???

4Ch

BYTE

ISA I/O recovery timer register (see #01087)

4Dh

BYTE

part revision register (see #01088)

4Eh

BYTE

X-bus Chip Select A register (see #01089)

4Fh

BYTE

X-bus Chip Select B register??? (see also #01102)

50h

BYTE

host select register

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 (i.e. C0h = 1/4, 80h = 1/2, 40h = 3/4, 20h = 7/8, etc.)

52h

WORD

secondary (L2) cache control register

54h

2 BYTEs

???

56h

WORD

DRAM control register

58h

BYTE

???

59h

7 BYTEs

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

60h

5 BYTEs

DRAM row boundary registers 0-4
each register N indicates amount of memory in rows 0-N (each row is 64 bits wide); the fifth row of memory (if implemented) must contain either 8M or 16M, depending on system configuration
boundary register 4 (offset 64h) contains the total system memory, which may not exceed 128M

65h

BYTE

???

66h

BYTE

PIRQ route control register 0

67h

BYTE

PIRQ route control register 1

68h

BYTE

DRAM memory hole register

69h

BYTE

top of memory

6Ah

6 BYTEs

???

70h

BYTE

SMRAM control register

71h

47 BYTEs

unused???

A0h

BYTE

SMI control register

A1h

BYTE

???

A2h

WORD

SMI enable register

A4h

DWORD

system event enable

A8h

BYTE

fast off timer register

A9h

BYTE

???

AAh

WORD

SMI request register

ACh

BYTE

clock throttle STPCLK# low timer

ADh

BYTE

unused???

AEh

BYTE

clock throttle STPCLK# high timer

AFh

BYTE

???

B0h

80 BYTEs

unused???

See Also:

#00878,#01063,#01055,#01108,#01167