
Hawk PCI Host Bridge & Multi-Processor Interrupt Controller
MVME5100 Single Board Computer Programmer’s Reference (6806800H17B)
91
The second step is to either read or write configuration data into the CONFIG_DATA register. If
the CONFIG_ADDRESS register is set up correctly, the PHB will pass this access on to the PCI bus
as a configuration cycle.
The addresses of the CONFIG_ADDRESS and CONFIG_DATA registers are actually embedded
within PCI I/O space. If the CONFIG_ADDRESS register has been set incorrectly or the access to
either the CONFIG_ADDRESS or CONFIG_DATA register is not 1, 2, or 4 bytes wide, the PHB will
pass the access on to PCI as a normal I/O Space transfer.
The CONFIG_ADDRESS register is located at offset $CF8 from the bottom of PCI I/O space. The
CONFIG_DATA register is located at offset $CFC from the bottom of PCI I/O space. The PHB
address decode logic has been designed such that XSADD3 and XSOFF3 must be used for
mapping to PCI Configuration (consequently I/O) space. The XSADD3/XSOFF3 register group
is initialized at reset to allow PCI I/O access starting at address $80000000. The powerup
location (Little Endian disabled) of the CONFIG_ADDRESS register is $80000CF8, and the
CONFIG_DATA register is located at $80000CFC.
The CONFIG_ADDRESS register must be prefilled with four fields: the Register Number, the
Function Number, the Device Number, and the Bus Number.
The Register Number and the Function Number get passed along to the PCI bus as a portion of
the lower address bits.
When performing a configuration cycle, the PHB uses the upper 20 address bits as IDSEL lines.
During the address phase of a configuration cycle, only one of the upper address bits will be set.
The device that has its IDSEL connected to the address bit being asserted is selected for a
configuration cycle. The PHB decodes the Device Number to determine which of the upper
address lines to assert. The decoding of the five-bit Device Number is shown in the following
table:
Table 2-11 Device Number Decoding
Device Number
Address Bit
00000
AD31
00001 - 01010
All Zeros
01011
AD11
01100
AD12
(etc.)
(etc.)
Содержание MVME5100
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