AMD SB700/710/750 Register Programming Requirements

2.13 Legacy DMA Prefetch Enhancement
ASIC Rev Register Settings Function/Comment
All Revs SB7x0 Smbus_PCI_config 0x43 [0] = 1 (only when
the system is non-DOS mode)
All Revs SB7x0 Smbus_PCI_config 0x41 [7] = 1
Lpc_PCI_config 0x78 [0] = 0
SATA USB SMBUS PATA AC97 HD AUDIO LPC PCI
X
RTC ACPI PM REG A-LINK I/O REG XIOAPIC
2.14 USB Set BM_STS
Enables legacy DMA prefetch enhancement for channel 0,
1, 2, and 3. This bit should be set to improve DMA out (eg
memory-to-floppy disk) performance.
Note: This bit should only be enabled in the ACPI method
(called by the OS). This ensures that it is enabled only
when the system is in Window mode. Under DOS mode,
this feature may not work properly and may cause the
floppy to malfunction.
Set these bits to make LPC DMA work properly.
ASIC Rev Register Settings Function/Comment
For register details, refer to
the sections check-marked
in the SB700/710/750
Register Reference Guide.
All Revs SB7x0 PM_IO 0x66 [6] = 0 For balanced power saving and USB performance, allow
USB DMA to cause pop-up. Other register settings for C
state should be followed for the system to work properly.
Note: Refer to USB register settings section for the corresponding USB register settings that are required to be
programmed when the above registers are programmed. For the AMD platform, PM_IO 0x66 [6], and register settings in
the USB register settings section should be programmed.
SATA USB SMBUS PATA AC97 HD AUDIO LPC PCI
RTC ACPI PM REG A-LINK I/O REG XIOAPIC
x
2.15 Enabling Spread Spectrum
ASIC Rev Register Settings Function/Comment
All Revs SB7x0 PM_IO 0x42 [7] = 1
SATA USB SMBUS PATA AC97 HD AUDIO LPC PCI
RTC ACPI PM REG A-LINK I/O REG XIOAPIC
x
For register details, refer to
the sections check-marked
in the SB700/710/750
Register Reference Guide.
Enables Spread Spectrum on PCI clocks with -0.5%
spread. In external clock mode, the internal SS when
enabled will down spread the PCI clocks. The 100 MHz
PCIE clock SB_SRC from External Clock generator should
not have Spread Spectrum enabled if the internal Spread
is enabled. Refer to PA_SB700AGx for more information
on enabling the Spread Spectrum.
For register details, refer to
the sections check-marked
in the SB700/710/750
Register Reference Guide.
© 2009 Advanced Micro Devices, Inc. ACPI/SMBUS Controller (bus-0, dev-20, fun-0)
AMD SB700/710/750 Register Programming Requirements Page 16