GXM Datasheet, PDF (28/244 Pages) National Semiconductor (TI) – Geode™ GXm Processor Integrated x86 Solution with MMX Support

Signal Definitions (Continued)
2.2.2 PCI Interface Signals (Continued)
Signal Name
BGA SPGA
Pin No. Pin No
Type
LOCK#
B11
B16
s/t/s
(PU)
(PU)
DEVSEL#
A9
E15
s/t/s
(PU)
(PU)
PERR#
A11
D16
s/t/s
(PU)
(PU)
SERR#
C12
A17
OD
(PU)
(PU)
REQ[2:0]#
D3,
E3,
I
H3,
K2,
E3
E1
(PU)
(PU)
Description
Lock Operation
LOCK# indicates an atomic operation that may require multiple
transactions to complete. When LOCK# is asserted, nonexclu-
sive transactions may proceed to an address that is not currently
locked (at least 16 bytes must be locked). A grant to start a trans-
action on PCI does not guarantee control of LOCK#. Control of
LOCK# is obtained under it own protocol in conjunction with
GNT#. It is possible for different agents to use PCI while a single
master retains ownership of LOCK#. The arbiter can implement
a complete system lock. In this mode, if LOCK# is active, no
other master can gain access to the system until the LOCK# is
deasserted.
This pin is internally connected to a 20-kohm pull-up resistor.
Device Select
DEVSEL# indicates that the driving device has decoded its
address as the target of the current access. As an input,
DEVSEL# indicates whether any device on the bus has been
selected. DEVSEL# will also be driven by any agent that has the
ability to accept cycles on a subtractive decode basis. As a mas-
ter, if no DEVSEL# is detected within and up to the subtractive
decode clock, a master abort cycle will result expect for special
cycles which do not expect a DEVSEL# returned.
This pin is internally connected to a 20-kohm pull-up resistor.
Parity Error
PERR# is used for reporting of data parity errors during all PCI
transactions except a Special Cycle. The PERR# line is driven
two SYSCLKs after the data in which the error was detected.
This is one SYSCLK after the PAR that is attached to the data.
The minimum duration of PERR# is one SYSCLK for each data
phase in which a data parity error is detected. PERR# must be
driven high for one SYSCLK before being in TRI-STATE mode. A
target asserts PERR# on write cycles if it has claimed the cycle
with DEVSEL#. The master asserts PERR# on read cycles.
This pin is internally connected to a 20-kohm pull-up resistor.
System Error
System Error may be asserted by any agent for reporting errors
other than PCI parity. The intent is to have the PCI central agent
assert NMI to the processor. When the Parity Enable bit is set in
the Memory Controller Configuration register, SERR# will be
asserted upon detecting a parity error on read operations from
DRAM.
Request Lines
Request indicates to the arbiter that an agent desires use of the
bus. Each master has its own REQ# line. REQ# priorities are
based on the arbitration scheme chosen.
Each of these pins are internally connected to a 20-kohm pull-up
resistor.
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