MSC8144E Reference Manual, Rev. 3
15-8
Freescale
Semiconductor
PCI
Figure 15-4. Burst Write Example
A write transaction is similar to a read transaction except no turnaround cycle is needed following
the address phase because the initiator provides both address and data. Data phases are the same
for both read and write transactions.
15.1.8.2 Transaction Termination
The termination of a PCI transaction is orderly and systematic, regardless of the cause of the
termination. All transactions end when
PCI_FRAME
and
PCI_IRDY
are both deasserted, indicating
the idle cycle.
The VCOP as an initiator terminates a transaction when
PCI_FRAME
is deasserted and
PCI_IRDY
is
asserted. This indicates that the final data phase is in progress. The final data transfer occurs
when both
PCI_TRDY
and
PCI_IRDY
are asserted. An initiator-abort is an abnormal case of an
initiator initiated termination. If the VCOP detects that
PCI_DEVSEL
has remained deasserted for
more than four clocks after the assertion of
PCI_FRAME
, it deasserts
PCI_FRAME
and then, on the
next clock, deasserts
PCI_IRDY
. On aborted reads, the VCOP returns 0xFFFF_FFFF. The data is
lost on aborted writes.
When the VCOP as a target needs to suspend a transaction, it asserts
PCI_STOP
. Once asserted,
PCI_STOP
remains asserted until
PCI_FRAME
is deasserted. Depending on the circumstances, data
may or may not be transferred during the request for termination. If
PCI_TRDY
and
PCI_IRDY
are
asserted during the assertion of
PCI_STOP
, data is transferred. This type of target-initiated
termination is called a disconnect B, shown in Figure 15-5. If
PCI_TRDY
is asserted when
PCI_STOP
is asserted but
PCI_IRDY
is not,
PCI_TRDY
must remain asserted until
PCI_IRDY
is
asserted and the data is transferred. This is called a “disconnect A” target-initiated termination,
also shown in Figure 15-5. However, if
PCI_TRDY
is deasserted when
PCI_STOP
is asserted, no
more data is transferred, and the initiator therefore does not have to wait for a final data transfer
(see the retry diagram in Figure 15-5).
ADDR
CMD
PCI_CLK
PCI_AD[31–0]
PCI_C/BE[3–0]
PCI_FRAME
PCI_IRDY
PCI_DEVSEL
PCI_TRDY
DATA4
DATA1
DATA2
DATA3
BEs 1
BEs 2
BEs 3
BEs 4
Содержание MSC8144E
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Страница 452: ...MSC8144E Reference Manual Rev 3 11 38 Freescale Semiconductor Internal Memory Subsystem ...
Страница 520: ...MSC8144E Reference Manual Rev 3 12 68 Freescale Semiconductor DDR SDRAM Memory Controller ...
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