Pci Bus Commands - Motorola MPC8240 User Manual

PCI Bus Protocol
PCI Bus
C/BE[3:0]
Command
0000 Interrupt-
acknowledge
0001 Special cycle
0010 I/O-read
0011 I/O-write
1
0100 Reserved
1
0101 Reserved
0110 Memory-read
0111 Memory-write
1
1000 Reserved
1
1001 Reserved
1010 Configuration-
read
1011 Configuration-
write
7-10
Table 7-2. PCI Bus Commands
MPC8240 MPC8240
Supports as Supports
an Initiator as a Target
Yes No
Yes No
Yes No
Yes No
No No
No No
Yes Yes
Yes Yes
No No
No No
Yes Yes
Yes Yes
MPC8240 Integrated Processor User's Manual
Definition
The interrupt-acknowledge command is a read (implicitly
addressing the system interrupt controller). Only one
device on the PCI bus should respond to the
interrupt-acknowledge command. Other devices ignore
the interrupt-acknowledge command. See
Section 7.4.6.1, "Interrupt-Acknowledge Transactions,"
for more information.
The special-cycle command provides a mechanism to
broadcast select messages to all devices on the PCI bus.
See Section 7.4.6.2, "Special-Cycle Transactions," for
more information.
The I/O-read command accesses agents mapped into
the PCI I/O space.
The I/O-write command accesses agents mapped into
the PCI I/O space.
The memory-read command accesses either local
memory or agents mapped into PCI memory space,
depending on the address. When a PCI master issues a
memory-read command to local memory, the MPC8240
(the target) fetches data from the requested address to
the end of the cache line (32 bytes) from local memory,
even though all of the data may not be requested by (or
sent to) the initiator.
The memory-write command accesses either local
memory or agents mapped into PCI memory space,
depending on the address.
The configuration-read 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, "Configuration
Cycles," for more detail on PCI configuration cycles.
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 on PCI
configuration accesses.
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