s5920 Applied Micro Circuits Corporation (AMCC), s5920 Datasheet - Page 108

• Manufacturer Part Number: s5920
• Description: Pci Product
• Manufacturer: Applied Micro Circuits Corporation (AMCC)

S5920 – PCI Product: PCI Bus Protocol
PCI BUS INTERRUPTS
The S5920 controller is able to generate PCI bus inter-
rupts by asserting the PCI bus interrupt signal (INTA#).
INTA# is a multi-sourced, wire-ORed signal on the PCI
bus and is driven by an open drain output on the
S5920. The assertion and deassertion of INTA# have
no fixed timing relationship with respect to the PCI bus
clock. Once the S5920 asserts INTA#, it remains
asserted until the interrupt source is cleared by a write
to the Interrupt Control/Status Register (INTCSR). In
the case of the external Add-On Interrupt, INTA# will
remain set as long as the ADDINT# pin is driven low
by an Add-On device(s). The source(s) driving ADD-
INT# must deassert this input before the PCI interrupt
(INTA#) is driven to the false state. It is the responsibil-
ity host software to clear the Add-On interrupt source
before exiting its interrupt handler routine.
PCI BUS PARITY ERRORS
The PCI specification defines two error-reporting sig-
nals, PERR# and SERR#. These signals indicate a
parity error condition on the signals AD[31:0], C/
BE[3:0]#, and PAR. The validity of the PAR signal is
delayed one clock period from its corresponding
AD[31:0] and C/BE[3:0]# signals. Even parity is sup-
ported by PCI: when the total number of ones in the
group of signals AD[31:0] and C/BE[3:0]# is equal to
an even number the parity bit will be deasserted. If an
odd number of ones is seen, the parity bit will be
asserted.
PERR# is the error-reporting mechanism for parity
errors that occur during the data phase for all but PCI
Special Cycle commands. SERR# is the error-report-
ing mechanism for parity errors that occur during the
address phase.
The timing diagram in Figure 9 shows the timing rela-
tionships between the signals AD[31:0], C/BE[3:0]#,
PAR, PERR# and SERR#.
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The S5920 asserts SERR# if it detects odd parity dur-
ing an address phase, if enabled. The SERR# enable
bit is bit 8 in the S5920 PCI Command Register
(PCICMD). The odd parity error condition involves the
state of signals AD[31:0] and C/BE[3:0]# when
FRAME# is first asserted and the PAR signal during
the following clock. If an error is detected, the S5920
asserts SERR# on the following (after PAR valid)
clock. Since many targets may observe an error on an
address phase, the SERR# signal is an open-drain
multi-sourced, wire-ORed signal on the PCI bus. The
S5920 drives SERR# low for one clock period when
an address phase error is detected. Once an SERR#
error is detected by the S5920, the PCI Status register
bit 14, System Error, is set and remains set until
cleared through software or a hardware reset.
The PERR# signal is similar to the SERR# with two
differences: it reports errors for the data phase and is
only asserted by the device receiving the data. The
S5920 drives this signal (removed from tri-state) when
it is the selected target for write transactions. The par-
ity error conditions are only reflected by the PERR#
pin if the Parity Error Enable bit (bit 6) of the PCI Com-
mand Register is set. Upon the detection of a data
parity error, the Detected Parity Error bit (bit 15) of the
PCI Status Register is set (PCISTS). Unlike the
PERR# signal pin, this Status bit is set regardless of
the state of the PCI Command Register's Parity Error
Enable bit.
The assertion of PERR# occurs two clock periods fol-
lowing the data transfer. This two-clock delay occurs
because the PAR signal does not become valid until
the clock following the transfer, and an additional clock
is provided to generate and assert PERR# once an
error is detected. PERR# is only asserted for one
clock cycle for each error sensed. The S5920 only
qualifies the parity error detection during the actual
data transfer portion of a data phase (when both
IRDY# and TRDY# are asserted).
Revision 1.02 – April 12, 2007
Data Book
DS1596
108