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User’s Manual
48 ECB-865 User’s Manual
3.11.38.4 Arbitration
REQ#
Request indicates to the arbiter that this agent desires use of the bus. This is a point
to point signal. Every master has its own REQ# which must be tri-stated while RST#
is asserted.
GNT#
Grant indicates to the agent that access to the bus has been granted. This is a point
to point signal. Every master has its own GNT# which must be ignored while RST# is
asserted.
3.11.38.5 Error Reporting
PERR#
Parity Error is only for the reporting of data parity errors during all PCI transactions
except a Special Cycle. The PERR# pin is sustained tri-state and must be driven
active by the agent receiving data two clocks following the data when a data parity
error is detected. The minimum duration of PERR# is one clock for each data phase
that a data parity error is detected. (If sequential data phases each have a data parity
error, the PERR# signal will be asserted for more than a single clock.) PERR# must
be driven high for one clock before being tri-stated as with all sustained tri-state
signals. There are no special conditions when a data parity error may be lost or when
reporting of an error may be delayed. An agent cannot report a PERR# until it has
claimed the access by asserting DEVSEL# (for a target) and completed a data phase
or is the master of the current transaction.
SERR#
System Error is for reporting address parity errors, data parity errors on the Special
Cycle command, or any other system error where the result will be catastrophic. If an
agent does not want a non-maskable interrupt (NMI) to be generated, a different
reporting mechanism is required. SERR# is pure open drain and is actively driven for
a single PCI clock by the agent reporting the error. The assertion of SERR# is
synchronous to the clock and meets the setup and hold times of all bused signals.
However, the restoring of SERR# to the deasserted state is accomplished by a weak
pullup (same value as used for s/t/s) which is provided by the system designer and
not by the signaling agent or central resource. This pullup may take two to three
clock periods to fully restore SERR#. The agent that reports SERR#s to the
operating system does so anytime SERR# is sampled asserted.