Advanced Configuration and Power Interface Specification

Device Configuration
6.4.2 Small Resource Data Type
A small resource data type may be 2 to 8 bytes in size and adheres to the following format:
Table 6-190 Small Resource Data Type Tag Bit Definitions
Offset
Field
Byte 0 Tag Bit [7] Tag Bits [6:3] Tag Bits [2:0]
Type–0 (Small item) Small item name Length–n bytes
Bytes 1 to n Data bytes (Length 0 – 7)
The following small information items are currently defined for Plug and Play devices:
Table 6-191 Small Resource Items
Small Item Name
Reserved
IRQ Format Descriptor
DMA Format Descriptor
Start Dependent Functions Descriptor
End Dependent Functions Descriptor
I/O Port Descriptor
Fixed Location I/O Port Descriptor
Fixed DMA Descriptor
Reserved
Vendor Defined Descriptor
End Tag Descriptor
Value
0x00-0x03
0x04
0x05
0x06
0x07
0x08
0x09
0x0A
0x0B–0x0D
0x0E
0x0F
6.4.2.1 IRQ Descriptor
Type 0, Small Item Name 0x4, Length = 2 or 3
The IRQ data structure indicates that the device uses an interrupt level and supplies a mask with bits
set indicating the levels implemented in this device. For standard PC-AT implementation there are
15 possible interrupts so a two-byte field is used. This structure is repeated for each separate
interrupt required.
Table 6-192 IRQ Descriptor Definition
Offset Field Name
Byte 0 Value = 0x22 or 0x23 (0010001nB) – Type = 0, Small item name = 0x4, Length = 2 or 3
Byte 1 IRQ mask bits[7:0], _INT
Bit [0] represents IRQ0, bit[1] is IRQ1, and so on.
Byte 2 IRQ mask bits[15:8], _INT
Bit [0] represents IRQ8, bit[1] is IRQ9, and so on.
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