82801BA Datasheet, PDF (299/498 Pages) Intel Corporation – Intel 82801BA I/O Controller Hub 2 (ICH2) and Intel 82801BAM I/O Controller Hub 2 Mobile

LPC Interface Bridge Registers (D31:F0)
9.4.8
OCW2—Operational Control Word 2 Register
Offset Address:
Default Value:
Master Controller–020h
Attribute:
Slave Controller–0A0h
Size:
Bit[4:0]=undefined, Bit[7:5]=001
WO
8 bits
Following a part reset or ICW initialization, the controller enters the fully nested mode of
operation. Non-specific EOI without rotation is the default. Both rotation mode and specific EOI
mode are disabled following initialization.
Bit
Description
Rotate and EOI Codes (R, SL, EOI)—WO. These three bits control the Rotate and End of Interrupt
modes and combinations of the two.
000 = Rotate in Auto EOI Mode (Clear)
001 = Non-specific EOI command
010 = No Operation
7:5 ^{011 = Specific EOI Command}
100 = Rotate in Auto EOI Mode (Set)
101 = Rotate on Non-Specific EOI Command
110 = *Set Priority Command
111 = *Rotate on Specific EOI Command
*L0–L2 Are Used
4:3 OCW2 Select—WO. When selecting OCW2, bits 4:3 = “00”
Interrupt Level Select (L2, L1, L0)—WO. L2, L1, and L0 determine the interrupt level acted upon
when the SL bit is active. A simple binary code, outlined below, selects the channel for the command
to act upon. When the SL bit is inactive, these bits do not have a defined function; programming L2,
L1 and L0 to 0 is sufficient in this case.
2:0 ^Bits
000
Interrupt Level
IRQ0/8
Bits
Interrupt Level
100
IRQ4/12
001
IRQ1/9
101
IRQ5/13
010
IRQ2/10
110
IRQ6/14
011
IRQ3/11
111
IRQ7/15
82801BA ICH2 and 82801BAM ICH2-M Datasheet
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