Functional Description
MSC8144E Reference Manual, Rev. 3
Freescale Semiconductor
15-5
incrementing burst order. The VCOP checks
AD[1–0]
during a memory command access and
provides the linear incrementing burst order. On reads, if
AD[1–0]
is 0b10, which represents a
cache line wrap, the VCOP linearly increments the burst order starting at the critical 64-bit
address, wraps at the end of the cache line, and disconnects after reading one cache line. If
AD[1–0]
is 0bx1 (a reserved encoding) and the
PCI_C/BE[3–0]
signals indicate a memory transaction, it
executes a target disconnect after the first data phase is completed. Note that
AD[1–0]
are included
in parity calculations.
15.1.5 Device Selection
As a target, the VCOP drives
PCI_DEVSEL
one clock following the address phase as indicated in
the configuration space status register; see page 15-24 for more information. The VCOP as a
target qualifies the address/data lines with
PCI_FRAME
before asserting
PCI_DEVSEL
. The
PCI_DEVSEL
signal is asserted at or before the clock edge at which the VCOP enables its
PCI_TRDY
,
PCI_STOP
, or data (for a read). The
PCI_DEVSEL
signal is not deasserted until
PCI_FRAME
is deasserted, with
PCI_IRDY
asserted and either
PCI_STOP
or
PCI_TRDY
asserted. The
exception to this is a target-abort; see Section 15.1.8.2 for more information. As an initiator, if
the VCOP does not see the assertion of
PCI_DEVSEL
within 4 clocks of
PCI_FRAME
, it terminates
the transaction with an initiator-abort as described in Section 15.1.8.2.
15.1.6 Byte Enable Signals
The byte enable signals (
BE[3–0]
) indicate which byte lanes carry valid data. The byte enable
signals may enable different bytes for each of the data phases. The byte enable signals are valid
on the edge of the clock that starts each data phase and remain valid for the entire data phase.
If the VCOP, as a target, sees no byte enable signals asserted, it completes the current data phase
with no permanent change. This implies that on a read transaction, the VCOP expects the data not
to be changed, and on a write transaction, the data is not stored.
15.1.7 Bus Driving and Turnaround
The turnaround-cycle is one clock cycle and is required to avoid contention. This cycle occurs at
different times for different signals.
PCI_IRDY
,
PCI_TRDY
, and
PCI_DEVSEL
use the address phase
as their turnaround-cycle.
PCI_FRAME
,
PCI_C/BE[3–0]
, and
AD[31–0]
use the idle cycle between
transactions as their turnaround-cycle. (An idle cycle in PCI is when both
PCI_FRAME
and
PCI_IRDY
are deasserted). Byte lanes not involved in the current data transfer are driven to a stable
condition even though the data is not valid.
Содержание MSC8144E
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Страница 314: ...MSC8144E Reference Manual Rev 3 8 24 Freescale Semiconductor General Configuration Registers ...
Страница 414: ...MSC8144E Reference Manual Rev 3 10 14 Freescale Semiconductor MSC8144E SC3400 DSP Subsystem ...
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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