Intel
®
81341 and 81342—Clocking and Reset
Intel
®
81341 and 81342 I/O Processors
Developer’s Manual
December 2007
994
Order Number: 315037-002US
19.2.2
Software Reset
In addition to the fundamental resets, 81341 and 81342 provides software control to
reset the internal bus, and Intel XScale
®
processor. Reset straps are not re-sampled
due to these resets.
•
Internal Bus Reset Bit
— This reset can be initiated in two ways. The first is by
writing to the coordinated reset bits in the MU
Section 4.9.4, “Inbound Interrupt
Status Register - IISR” on page 429
. The second is via the watchdog timer as
Section 12.1.2, “Watch Dog Timer Operation” on page 809
. This reset
is specific to the integrated I/O processor and the associated peripheral units. PCI
Configuration Registers are preserved through this reset. See
for more details.
• Intel XScale
®
Processor
Reset Bit
— This reset is initiated through the
HOLD_X0_IN_RST#
/
HOLD_X1_IN_RST#
“PCI Configuration and Status Register - PCSR” on page 183
, or the ATUE
3.16.41, “PCI Configuration and Status Register - PCSR” on page 331
. Once
invoked, the Intel XScale
®
processors are held in reset until released by software.
See
Section 19.2.7, “Intel XScale® Processor Reset Mechanism”
for more details.
•
Targeted Core Reset
— The Targeted Core reset can be used by an Intel XScale
®
processor to imitate a reset to another core in the system, including itself.
19.2.3
Secondary Bus Reset
When operating as a root complex or central resource, the following ‘secondary bus’
resets apply. Reset straps are not re-sampled due to these resets.
•
PCI Express Hot Reset
— When operating as a root complex, the ATUE can
generate the PCI Express Hot Reset sequence in order to reset the downstream
components on the PCI Express interface. This is accomplished by setting bit 0 of
the
“PCI Express Link Control/Status Register - PELCSR” on page 338
in the
ATUE.(
)
•
PCI Bus Reset
— When operating as the central resource on the PCI/X bus, the
P_RSTOUT# output can be used to reset the downstream PCI bus. This is
accomplished by writing to bit 21 of the
“PCI Configuration and Status Register -
). Bit 21 of PCSR defaults to a ‘1’.
It is the responsibility of the firmware to clear the Central Resource PCI Bus Reset
bit. After firmware clears bit 21 of PCSR hardware keeps the P_RSTOUT# signal
asserted (low) for about 300uS - the hardware waits about 150uS to allow the PLL
to warm-up and another 150uS to allow the clocks to stabilize. Therefore, firmware
has to wait about 300 uS after clearing bit 21 of PCSR. After the 300uS has
elapsed, hardware de-asserts the P_RSTOUT# signal. After P_RSTOUT# de-
asserts, firmware has to wait before issuing the first configuration cycle in order to
meet the PCI timing parameter Trhfa (about 2
26
PCI clocks). Note that the PCI
timing parameter Trhfa is dependent on the PCI bus speed selected.