Pci Interrupts - GE V7865 Series Hardware Reference Manual

2.5.2 PCI Interrupts

The Tsi148 VME Bridge and the PMC site of the V7865 connect Standard PCI
Interrupt Lines to the PCI-E to PCI-X bridge as shown in Figure 2-1 on page 37.
The PCI-E bridges (PLX PEX8114) convert the PCI INTx interrupts into virtual
PCI Express INTA interrupts that are signaled back to the chipset over the PCI
Express Interface.
Interrupts on Peripheral Component Interconnect (PCI) Local Bus are optional
and defined as "level sensitive," asserted low (negative true), using open drain
output drivers. The assertion and de-assertion of an interrupt line, INTx#, is
asynchronous to CLK. A device asserts its INTx# line when requesting attention
from its device driver. Once the INTx# signal is asserted, it remains asserted until
the device driver clears the pending request. When the request is cleared, the
device de-asserts its INTx# signal.
PCI defines one interrupt line for a single function device and up to four interrupt
lines for a multifunction device or connector. For a single function device, only
INTA# may be used while the other three interrupt lines have no meaning.
Figure 2-1 on page 37 depicts the V7865 interrupt logic pertaining to timer
NVRAM operations and the PCI expansion site.
Any function on a multifunction device can be connected to any of the INTx#
lines. The Interrupt Pin register defines which INTx# line the function uses to
request an interrupt. If a device implements a single INTx# line, it is called INTA#;
if it implements two lines, they are called INTA# and INTB#; and so forth. For a
multifunction device, all functions may use the same INTx# line, or each may
have its own (up to a maximum of four functions), or any combination thereof. A
single function can never generate an interrupt request on more than one INTx#
line.
The slave PIC accepts the PCI interrupts through lines that are defined by the
BIOS. The BIOS defines which interrupt line to utilize depending on which
system requires the use of the line.
Standard Features 35
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