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©2008 Advanced Micro Devices, Inc.
SMBus Module and ACPI Block (Device 20, Function 0)
AMD SB600 Register Reference Manual Proprietary Page 103
DmaLimit- RW - 8 bits - [PCI_Reg: 42h]
Field Name Bits Default Description
DmaBurstLimit 6:0 00h Enables the amount of burst data the legacy DMA engine can
sustain before it should give up the internal bus.
DmaLimitEnable 7 0h This is another enhancement to the legacy DMA engine. In
the original design, certain DMA request (such as Infrared) will
cause the legacy DMA engine to dominate the internal bus for
a very long time (up to 512 bytes) and thereby causing long
latency for other devices. Setting this bit will cause the legacy
DMA engine to limit its transfer per burst based on bits [6:0]
DmaLimit register
DmaPrefetchEnable RW - 8 bits - [PCI_Reg: 43h]
Field Name Bits Default Description
DmaPrefetchEnable 0 1b Legacy read DMA prefetch function enable.
1 – Enable
0 – Disable
When set, the DMA engine will keep the data inside the FIFO,
even though the requesting device has deasserted the DMA
request. When the device requests data again, the DMA
engine will have data available instead of having to fetch data
from the memory again. Note this enhancement only applies to
channel 0, 1, 2, and 3. It has no effect on channel 5, 6, or 7
Reserved 7:1 00h
DmaPrefetchEnable register
ISA Address Decode Control Register #1- RW - 8 bits - [PCI_Reg: 48h]
Field Name Bits Default Description
Window 0 0 1b 896K to 960K PCI enable
Window 1 1 1b 640K to 768K PCI enable
Window 2 2 1b 512K to 640K PCI enable
Window 3 3 1b 0K to 512K PCI enable
Reserved 7:4 0h
ISA Address Decode Control Register #1: This register defines the enable bits for four memory segments. If the
enable bit is set to 1, an ISA master or DMA access to the memory segment associated with that bit is forwarded to
the internal bus. The SB600 does not have any ISA master, because the bus is internal; however, it may affect
DMA transfers with the LPC module. Software should set all these bits to 1's.
ISA Address Decode Control Register #2- RW - 8 bits - [PCI_Reg: 49h]
Field Name Bits Default Description
Window 0 0 1b C0000h to C3FFFh
Window 1 1 1b C4000h to C7FFFh
Window 2 2 1b C8000h to CBFFFh
Window 3 3 1b CC000h to CFFFFh
Window 4 4 1b D0000h to D3FFFh
Window 5 5 1b D4000h to D7FFFh
Window 6 6 1b D8000h to DBFFFh
Window 7 7 1b DC000h to DFFFFh
ISA Address Decode Control Register #1: This register defines the PCI enable bits for four memory segments. If
the enable bit is set to 1, an ISA master or DMA access to the memory segment associated with that bit is forward
to the internal bus. The SB600 does not have any ISA master, because the bus is internal; however, it may affect
the DMA transfers with the LPC module. Software should set all these bits to 1's.