Window Base Registers (Wx_BASE, x=0-3)
Address: 87.6000.0400, 87.6000.0500, 87.6000.0600, 87.6000.0700
The Window Base Register (WBR) provides the base address for a particular target window. There are four WBRs: W_BASE[0], W_BASE[1], W_BASE[2], and W_BASE[3]. The W_BASE[x] registers should not be modified unless software insures that no PCI traffic is targeted for the window being modified.

Determining a Hit in the Target Window:

  • The incoming PCI address bits <31:20> are compared with the each of the four WBRs, where the W_MASK register determines which bits are involved in the comparison.
  • The Target Window is "Hit" when the masked addresses match a valid WBRs. If MEMCS_enable is set, then the "Hit" is further qualified by the MEMCS input signal -- this is used if PC compatibility holes are required in the PYXIS.
  • When DAC enable is set in Window 3, then W_DAC base register is used to compare PCI address<39:32> of a DAC cycle.
W_BASE<31:20>RW W_BASE specifies the PCI base address of the PCI Target Window and is used to determine a hit in the window. See MCES_ENABLE and DAC_ENABLE also.
Reserved<19:4>RO N/A
DAC_
ENABLE		<3>RW When the DAC_ENABLE bit is set, then the W_DAC register is compared against PCI address<39:32> for a PCI DAC cycle. If this compare "Hits," and the 32-bit portion of the PCI address "Hits," then a DAC cycle "Hit" occurs.
MEMCS_EN (only in W0_BASE)<2>RW When the MEMCS_EN bit is set then the MEMCS signal from the PCI ISA or PCI EISA bridge is ANDed with the normal window "Hit."
Wx_BASE
_SG		<1>RW When the Scatter/Gather bit is cleared, the PCI Target Window uses direct mapping to translate a PCI address to a CPU address. When the SG bit is set, the PCI Target Window uses Scatter/Gather mapping to translate a PCI address to a physical memory address.
W_EN<0>RW When W_EN is cleared, the PCI Target Window is disabled and will not be used to respond to PCI-initiated transfers. When W_EN is set, the PCI Target Window is enabled and will be used to respond to PCI-initiated transfers that "Hit" in the address range of the Target Window.