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Programmer’s Reference Manual 69
AC ’97 Audio Controller Registers (D30:F2)
2.1.11 NABMBAR—Native Audio Bus Mastering Base Address
Register (Audio—D30:F2)
Address Offset: 14h–17h Attribute: R/W, RO
Default Value: 00000001h Size: 32 bits
Lockable: No Power Well: Core
The Native PCI Mode Audio function uses PCI Base Address register #1 to request a contiguous
block of I/O space that is to be used for the Native Mode Audio software interface.
Note: The DMA registers for S/PDIF* and Microphone In 2 cannot be addressed via this address space.
These DMA functions are only available from the new MBBAR register. This register powers up
as read only and only becomes write-able when the IOSE bit in offset 41h is set.
2.1.12 MMBAR—Mixer Base Address Register (Audio—D30:F2)
Address Offset: 18h–1Bh Attribute: R/W, RO
Default Value: 00000000h Size: 32 bits
Lockable: No Power Well: Core
This BAR creates 512 bytes of memory space to signify the base address of the register space. The
lower 256 bytes of this space map to the same registers as the 256-byte I/O space pointed to by
NAMBAR. The lower 384 bytes are divided as follows:
• 128 bytes for the primary codec (offsets 00–7Fh)
• 128 bytes for the secondary codec (offsets 80–FFh)
• 128 bytes for the tertiary codec (offsets 100h–17Fh).
• 128 bytes of reserved space (offsets 180h–1FFh), returning all 0’s.
Bit Description
31:16 Hardwired to 0’s
15:6
Base Address — R/W. These bits are used in the I/O space decode of the Native Audio Bus
Mastering interface registers. The number of upper bits that a device actually implements depends
on how much of the address space the device will respond to. For AC '97 bus mastering, the upper
16 bits are hardwired to 0, while bits 15:6 are programmable. This configuration yields a maximum
I/O block size of 64 bytes for this base address.
5:1 Reserved. Read as 0’s.
0
Resource Type Indicator (RTE) — RO. This bit defaults to 0 and changes to 1 if the IOSE bit is set
(D30:F2:Offset 41h, bit 0). When 1, this bit indicates a request for I/O space.
Bit Description
31:9
Base Address — R/W. This field provides the lower 32-bits of the 512-byte memory offset to use for
decoding the primary, secondary, and tertiary codec’s mixer spaces.
8:3 Reserved. Read as 0’s.
2:1 Type — RO. Hardwired to 00b to Indicate the base address exists in 32-bit address space
0 Resource Type Indicator (RTE) — RO. Hardwired to 0 to indicate a request for memory space.