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MPC105 PCIB/MC User's Manual
MOTOROLA
7.3.3 Addressing
PCI defines three physical address spaces—PCI memory space, PCI I/O space, and PCI
configuration space. Access to the PCI memory and I/O space is straightforward, although
one must take into account the MPC105 memory map (A or B) being used. The memory
maps are described in Section 3.1, “Address Maps.” Access to the PCI configuration space
is described in Section 7.4.5, “Configuration Cycles.”
Address decoding on the PCI bus is performed by every device for every PCI transaction.
Each agent is responsible for decoding its own address. PCI supports two types of address
decoding—positive decoding and subtractive decoding. For positive decoding, each device
is looking for accesses in the address range that the device has been assigned. For
subtractive decoding, one device on the bus is looking for accesses that no other device has
claimed. See Section 7.3.4, “Device Selection,” for information about claiming
transactions.
1011
Configuration-write
Yes
No
The configuration-write command accesses
the 256-byte configuration space of a PCI
agent. A specific agent is selected when its
IDSEL signal is asserted during the address
phase. See Section 7.4.5.2, “Accessing the
PCI Configuration Space,” for more detail of
configuration accesses.
1100
Memory-read-multiple
No
Yes
The memory-read-multiple command
functions the same as the memory-read
command on the MPC105. If prefetching is
desired, speculative PCI reads should be
enabled. See Section 8.1.3.2.1,
“Speculative PCI Reads from System
Memory,” for more information.
1101
Dual-address-cycle
No
No
The dual-address-cycle command is used
to transfer a 64-bit address (in two 32-bit
address cycles) to 64-bit addressable
devices. The MPC105 does not respond to
this command.
1110
Memory-read-line
No
Yes
The memory-read-line command functions
the same as the memory-read command on
the MPC105.
1111
Memory-write-and-
invalidate
No
Yes
The memory-write-and-invalidate
command functions the same as the
memory-write command, but invalidates
any cache line hit that is marked dirty.
Note:
1
Reserved command encodings are reserved for future use. The MPC105 does not respond to these
commands.
Table 7-1. PCI Bus Commands (Continued)
C/BE3–
C/BE0
PCI Bus Command
MPC105
Supports
as a Master
Device
MPC105
Supports
as a Target
Device
Definition