Freescale Semiconductor MPC8260 9.9.1.2 PCI Protocol Fundamentals

PCI Bridge
MPC8260 PowerQUICC II Family Reference Manual, Rev. 2
Freescale Semiconductor 9-7
9.9.1.2 PCI Protocol Fundamentals
The bus transfer mechanism on the PCI bus is called a burst. A burst is comprised of an address phase and
one or more data phases.
All signals are sampled on the rising edge of the PCI clock. Each signal has a setup and hold window with
respect to the rising clock edge, in which transitions are not allowed. Outside this aperture, signal values
or transitions have no significance.
Table9- 2. PCI Command Definitions
PCI_C/BE[3-0] Command Type
Supported as:
Definition
Initiator Target
0b0000 Interrupt acknowledge YES NO A read implicitly addressed to the system interrupt
controller. The size of the vector to be returned is
indicated on the byte enables after the address phase.
0b0001 Special cycle YES NO Provides a simple message broadcast mechanism. See
Section 9.9.1.4.6, “Special C ycle Command.”
0b0010 I/O read YES NO Accesses agents mapped in I/O address space.
0b0011 I/O write YES NO Accesses agents mapped in I/O address space.
0b010x — — — Reserved. No response occurs.
0b0110 Memory read YES YES Accesses agents mapped in memory address space. A
read from prefetchable space, when seen as a target,
fetches a cache line of data (32 bytes) from the starting
address, even though all 32 bytes may not actually be
sent to the initiator.
0b0111 Memory write YES YES Accesses agents mapped in memory address space.
0b100x — — — Reserved. No response occurs.
0b1010 Configuration read YES YES Accesses the configuration space of each agent. An
agent is selected when its IDSEL signal is asserted. See
Section9.9.1.4.4, “Host Mode Configuration Access” for
more detail of configuration accesses. As a target, a
configuration read is only accepted if the PCI bridge is
configured to be in agent mode.
0b1011 Configuration write YES YES Accesses the configuration space of each agent. An
agent is selected when its IDSEL signal is asserted. See
Section9.9.1.4.4, “Host Mode Configuration Access”. As
a target, a configuration write is only accepted if the PCI
bridge is configured to be in agent mode.
0b1100 Memory read multiple YES YES Causes a prefetch of the next cache line.
0b1101 Dual address cycle NO NO Transfers an 8 byte address to devices.
0b1110 Memory read line YES YES Indicates that the initiator intends to transfer an entire
cache line of data.
0b1111 Memory write and
invalidate
NO YES Indicates that the initiator will transfer an entire cache line
of data, and if PCI has any cacheable memory, this line
needs to be invalidated.