SB82371 Intel Corporation, SB82371 Datasheet - Page 72

• Manufacturer Part Number: SB82371
• Description: 82371FB (PIIX) AND 82371SB (PIIX3) PCI ISA IDE XCELERATOR
• Manufacturer: Intel Corporation

82371FB (PIIX) AND 82371SB (PIIX3)
2.5.3.6.
I/O Address:
Default Value:
Attribute:
OCW1 sets and clears the mask bits in the Interrupt Mask Register (IMR). Each interrupt request line may be
selectively masked or unmasked any time after initialization. The IMR stores the interrupt line mask bits. The
IMR operates on the IRR. Masking of a higher priority input does not affect the interrupt request lines of lower
priority. Unlike status reads of the ISR and IRR, for reading the IMR, no OCW3 is needed. The output data
bus contains the IMR when an I/O read is active and the I/O address is 021h or 0A1h (OCW1). All writes to
OCW1 must occur following the ICW1-ICW4 initialization sequence, since the same I/O ports are used for
OCW1, ICW2, ICW3 and ICW4.
2.5.3.7.
I/O Address:
Default Value:
Attribute:
OCW2 controls both the Rotate Mode and the End of Interrupt Mode. Following a CPURST or ICW
initialization, the controller enters the fully nested mode of operation. Both rotation mode and specific EOI
mode are disabled following initialization.
72
7:0
7:5
4:3
Bit
Bit
Interrupt Request Mask (Mask [7:0]). When a 1 is written to any bit in this register, the
corresponding IRQx line is masked. For example, if bit 4 is set to a 1, then IRQ4 is masked.
Interrupt requests on IRQ4 do not set channel 4's interrupt request register (IRR) bit as long is
the channel is masked. When a 0 is written to any bit in this register, the corresponding IRQx
is unmasked. Note that masking IRQ2 on CNTRL-1 also masks the interrupt requests from
CNTRL-2, which is physically cascaded to IRQ2.
Rotate and EOI Codes. R, SL, EOI - These three bits control the Rotate and End of Interrupt
modes and combinations of the two. A chart of these combinations is listed above under the bit
definition.
Bits[7:5] Function Bits[7:5] Function
001
011
101
100
* L0 - L2 Are Used
OCW2 Select. Must be programmed to 00 selecting OCW2.
OCW1—Operational Control Word 1 Register
OCW2—Operational Control Word 2 Register
Non-specific EOI Cmd
Specific EOI Cmd
Rotate on Non-Specific EOI Cmd
Rotate in Auto EOI Mode (Set)
INT CNTRL-1—021h; INT CNTRL-2—0A1h
00h
Read/Write
INT CNTRL-1—020h; INT CNTRL-2—0A0h
Bit[4:0]=undefined; Bit[7:5]=001
Write Only
111
000
*Rotate on Specific EOI Cmd
Description
Description
Rotate in Auto EOI Mode (Clear)
110
010
*Set Priority Cmd
No Operation