MSC8144E Reference Manual, Rev. 3
15-4
Freescale
Semiconductor
PCI
15.1.3 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. PCI data transfers are controlled by the following three fundamental signals:
PCI_FRAME
is driven by an initiator to indicate the beginning and end of a transaction.
PCI_IRDY
(initiator ready) is driven by an initiator, allowing it to force wait cycles.
PCI_TRDY
(target ready) is driven by a target, allowing it to force wait cycles.
The bus is idle when both
PCI_FRAME
and
PCI_IRDY
are deasserted. The first clock cycle in which
PCI_FRAME
is asserted indicates the beginning of the address phase. The address and the bus
command code are transferred in that cycle. The next cycle ends the address phase and begins the
data phase.
During the data phase, data is transferred in each cycle that both
PCI_IRDY
and
PCI_TRDY
are
asserted. Once the VCOP, as an initiator, has asserted
PCI_IRDY
, it does not change
PCI_IRDY
or
PCI_FRAME
until the current data phase completes, regardless of the state of
PCI_TRDY
. Once the
VCOP, as a target, has asserted
PCI_TRDY
or
PCI_STOP
it does not change
PCI_DEVSEL
,
PCI_TRDY
,
or
PCI_STOP
until the current data phase completes.
When the VCOP (as an initiator) intends to complete only one more data transfer,
PCI_FRAME
is
deasserted and
PCI_IRDY
is asserted (or kept asserted) indicating the initiator is ready. After the
target indicates it is ready (
PCI_TRDY
asserted) the bus returns to the idle state.
15.1.4 Addressing
The PCI specification defines three physical address spaces—memory, I/O, and configuration.
The memory and I/O address spaces are standard for all systems. The configuration address space
has been defined specifically to support PCI hardware configuration. Each PCI device decodes
the address for each PCI transaction with each agent responsible for its own address decode. The
information contained in the two lower address bits (AD1 and AD0) depends on the address
space. In the I/O address space, all 32 address/data lines provide the full byte address.
AD[1–0]
are
used for the generation of
PCI_DEVSEL
and indicate the least significant valid byte involved in the
transfer. In the configuration address space, accesses are decoded to a 4-byte address using
AD[7–2]
. An agent determines if it is the target of the access when a configuration command is
decoded,
IDSEL
is asserted, and
AD[1–0]
are 0b00; otherwise, the agent ignores the current
transaction.
For memory accesses, the address is decoded using
AD[31–2]
; thereafter, the address is
incremented internally by 4 bytes until the end of the burst transfer. Another initiator in a
memory access should drive 0b00 on
AD[1–0]
during the address phase to indicate a linear
Summary of Contents for MSC8144E
Page 1: ...MSC8144E Reference Manual Quad Core Media Signal Processor MSC8144ERM Rev 3 July 2009 ...
Page 48: ...MSC8144E Reference Manual Rev 3 xlviii Freescale Semiconductor ...
Page 86: ...MSC8144E Reference Manual Rev 3 1 38 Freescale Semiconductor Overview ...
Page 168: ...MSC8144E Reference Manual Rev 3 3 60 Freescale Semiconductor External Signals ...
Page 242: ...MSC8144E Reference Manual Rev 3 5 26 Freescale Semiconductor Reset ...
Page 314: ...MSC8144E Reference Manual Rev 3 8 24 Freescale Semiconductor General Configuration Registers ...
Page 414: ...MSC8144E Reference Manual Rev 3 10 14 Freescale Semiconductor MSC8144E SC3400 DSP Subsystem ...
Page 452: ...MSC8144E Reference Manual Rev 3 11 38 Freescale Semiconductor Internal Memory Subsystem ...
Page 520: ...MSC8144E Reference Manual Rev 3 12 68 Freescale Semiconductor DDR SDRAM Memory Controller ...
Page 1070: ...MSC8144E Reference Manual Rev 3 21 28 Freescale Semiconductor Timers ...