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PCI Functional Description
2-3
2.1.1 PCI Addressing
There are three physical address spaces defined in the PCI specification:
PCI Configuration space
I/O space for operating registers
Memory space for operating registers
2.1.1.1 Configuration Space
The host processor uses this configuration space to initialize the
SYM53C1010. Two independent sets of configuration space registers are
defined, one set for each SCSI function. Each SCSI function contains the
same register set with identical default values except for the Interrupt Pin.
The configuration registers are initialized by the system BIOS using PCI
configuration cycles. Each configuration space is a contiguous 256 x
8-bit set of addresses. Decoding C_BE[3:0]/ determines if a PCI cycle is
intended to access the configuration register space. The IDSEL bus
signal is a “chip select” that allows access to the configuration register
space only. A configuration read/write cycle without IDSEL is ignored.
The host processor uses the eight lower order address bits (AD[7:0]) to
select a specific 8-bit register. Since the SYM53C1010 is a PCI
multifunction device, bits AD[10:8] decode either SCSI Function A
Configuration register (AD[10:8] = 0b000) or SCSI Function B
Configuration register (AD[10:8] = 0b001).
Figure 4.1
is an illustration of
the PCI Configuration Register Map.
At initialization time, each PCI device is assigned a base address for
memory and I/O accesses. In the SYM53C1010, the upper 24 bits of the
address are selected. On every access, the SYM53C1010 compares its
assigned base addresses with the value on the Address/Data bus during
the PCI address phase. If the upper 24 bits match, the access is
designated for the SYM53C1010. The low order eight bits define the
register to be accessed. A decode of C_BE[3:0]/ determines which
register and what type of access is performed.
2.1.1.2 I/O Space
The PCI specification defines I/O space as a contiguous 32-bit I/O
address that is shared by all system resources, including the