PCI6x21/PCI6x11 internal event, because it depends on the completion of applying power to the socket rather than
on a signal change at the PC Card interface.
3.7.2 Interrupt Masks and Flags
Host software may individually mask (or disable) most of the potential interrupt sources listed in Table 3−10 by setting
the appropriate bits in the PCI6x21/PCI6x11 controller. By individually masking the interrupt sources listed, software
can control those events that cause a PCI6x21/PCI6x11 interrupt. Host software has some control over the system
interrupt the PCI6x21/PCI6x11 controller asserts by programming the appropriate routing registers. The
PCI6x21/PCI6x11 controller allows host software to route PC Card CSC and PC Card functional interrupts to separate
system interrupts. Interrupt routing somewhat specific to the interrupt signaling method used is discussed in more
detail in the following sections.
When an interrupt is signaled by the PCI6x21/PCI6x11 controller, the interrupt service routine must determine which
of the events listed in Table 3−9 caused the interrupt. Internal registers in the PCI6x21/PCI6x11 controller provide
flags that report the source of an interrupt. By reading these status bits, the interrupt service routine can determine
the action to be taken.
Table 3−9 details the registers and bits associated with masking and reporting potential interrupts. All interrupts can
be masked except the functional PC Card interrupts, and an interrupt status flag is available for all types of interrupts.
Notice that there is not a mask bit to stop the PCI6x21/PCI6x11 controller from passing PC Card functional interrupts
through to the appropriate interrupt scheme. These interrupts are not valid until the card is properly powered, and
there must never be a card interrupt that does not require service after proper initialization.
Table 3−9 lists the various methods of clearing the interrupt flag bits. The flag bits in the ExCA registers (16-bit PC
Card-related interrupt flags) can be cleared using two different methods. One method is an explicit write of 1 to the
flag bit to clear and the other is by reading the flag bit register. The selection of flag bit clearing methods is made by
bit 2 (IFCMODE) in the ExCA global control register (ExCA offset 1Eh/5Eh/81Eh, see Section 5.20), and defaults to
the flag-cleared-on-read method.
The CardBus-related interrupt flags can be cleared by an explicit write of 1 to the interrupt flag in the socket event
register (see Section 6.1). Although some of the functionality is shared between the CardBus registers and the ExCA
registers, software must not program the chip through both register sets when a CardBus card is functioning.
3.7.3 Using Parallel IRQ Interrupts
The seven multifunction terminals, MFUNC6−MFUNC0, implemented in the PCI6x21/PCI6x11 controller can be
routed to obtain a subset of the ISA IRQs. The IRQ choices provide ultimate flexibility in PC Card host interruptions.
To use the parallel ISA-type IRQ interrupt signaling, software must program the device control register (PCI offset
92h, see Section 4.39), to select the parallel IRQ signaling scheme. See Section 4.36, Multifunction Routing Status
Register, for details on configuring the multifunction terminals.
A system using parallel IRQs requires (at a minimum) one PCI terminal, INTA, to signal CSC events. This requirement
is dictated by certain card and socket-services software. The INTA requirement calls for routing the MFUNC0 terminal
for INTA signaling. The INTRTIE bit is used, in this case, to route socket interrupt events to INTA. This leaves (at a
maximum) six different IRQs to support legacy 16-bit PC Card functions.
As an example, suppose the six IRQs used by legacy PC Card applications are IRQ3, IRQ4, IRQ5, IRQ9, IRQ10,
and IRQ15. The multifunction routing status register must be programmed to a value of 0A9F 5432h. This value
routes the MFUNC0 terminal to INTA signaling and routes the remaining terminals as illustrated in Figure 3−11. Not
shown is that INTA must also be routed to the programmable interrupt controller (PIC), or to some circuitry that
provides parallel PCI interrupts to the host.
3−17
TI [ TEXAS INSTRUMENTS ]
