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PCI Bus Controller
22-36
Freescale Semiconductor
22.4.3
Internal Bus Initiator Interface
The processor core or internal masters may access the PCI bus via the internal bus initiator interface. This
internal interface is accessed through three windows in the processor address space set up by base address
and base address mask registers (
Section 22.3.2.5, “Initiator Window n Base/Translation Address Register
). Valid values programmed to the initiator window base address field in the
PCIIW
n
BTAR registers include addresses within the crossbar switch slave port offset for the PCI
controller. The controller does not receive and, therefore, does not decode addresses outside the crossbar
switch slave port range. The base address registers must be enabled by setting their respective enable bits
in the PCIIWCR register (
Section 22.3.2.6, “Initiator Window Configuration Register (PCIIWCR)”
).
Accesses to this area translate into PCI transactions on the PCI bus. See
for examples on setting up address windows. An internal address within the crossbar switch
slave port range dedicated to PCI initiator space is not a hit on an PCIIW
n
BTAR[WBA] field results in an
internal error.
The PCI configuration bits associated with the address window (PCIIWCR) determines the particular type
of PCI transaction generated. For example, the user might set one window to do PCI
MEMORY
READ
MULTIPLE
accesses, one window for PCI
I
/
O
READ
or
I
/
O
WRITE
accesses, and the other window to do
non-prefetchable (memory-mapped I/O) PCI memory accesses. See
translations.
In addition to configurable address window mapping logic, the register interface provides a configuration
address register, which provides the ability to generate configuration, interrupt acknowledge, and special
cycles. This interface configures external PCI devices. See
Section 22.4.3.2, “Configuration Mechanism
”
for
CONFIGURATION
READ
/
WRITE
,
INTERRUPT
ACKNOWLEDGE
, and
SPECIAL
CYCLE
command support.
The internal bus initiator interface supports all internal bus transactions, including single-beat transfers and
bursts (16 bytes).
Internal bus initiator read requests are decoded into four types: PCI memory, I/O, configuration, and
interrupt acknowledge. The PCI controller acknowledges the read address and attempts to gain access to
the PCI bus to transfer read data. The address acknowledge may be delayed if posted write data moving in
the other direction, the target interface path, posts when the previous read queues. This allows the target
write data to complete to the internal bus before the PCI controller initiates a new PCI read transaction.
Internal bus initiator reads from PCI target space must obey PCI bridge ordering rules. The following
sequence of events occur for every read across the initiator path:
1. Before transferring read data on the PCI bus, all previously posted writes moving across this
interface complete first to the PCI bus.
2. The read performs on the PCI bus and queues in a buffer.
3. All posted writes moving in the other direction, across the internal bus target interface, and posted
before the read occurred on the PCI bus complete to the internal bus.
4. The queued read data is then sent back to the internal bus master.
A 16-byte read buffer stores read data in the PCI controller when received from the PCI bus. PCI targets
can disconnect in the middle of a transfer. If the target for an internal bus read from PCI disconnects part
way through the burst, the PCI controller may have to manage a local memory access from an alternate
Содержание MCF54455
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