Intel 460GX Software Developer’s Manual page 71

Table 2-10. I/O (x)APIC RTE Format (Cont'd)
Register Offset: 10-8Fh
SAPIC Mode
Bit(s)
Name
16 MASK
15 TRIGGER
MODE
14 RIRR
13 POLARITY
12 DELIVERY
STATUS
Intel® 460GX Chipset Software Developer's Manual
Default Value: Undefined except mask bit is 1Attribute: Read/Write
APIC Mode
Name
MASK This bit masks the (x)APIC delivery of this interrupt.
A 0 indicates that delivery of this interrupt is not masked. An edge or level on
an interrupt pin that is not masked results in the delivery of the interrupt to the
destination.
A 1 indicates that delivery of this interrupt is masked. It is the software's
responsibility to deal with the case where the mask bit is set after the interrupt
message has been accepted by a local (x)APIC unit but before the interrupt is
dispensed to the processor.
When the mask bit is 1, interrupts coming into the PID are routed to the INTIO,
I2O_INT#, or I2B pins, provided they are correctly mapped. No delivery status
bit latching is performed in this mode.
When the mask bit is a 0, interrupts are latched in the delivery status bit. If the
mask bit is set to a 1 after the interrupt is latched but before it is delivered, the
latched value will be held until the interrupt is unmasked and delivered.
TRIGGER The trigger mode field indicates the type of signal on the interrupt pin that
MODE triggers an interrupt.
A 0 indicates edge sensitive.
A 1 indicates level sensitive.
RIRR This bit is read-only. During (x)APIC mode, this bit is used for level-triggered
interrupts. Its meaning is undefined for edge-triggered interrupts. For level-
triggered interrupts, this bit is set when the local (x)APIC(s) accepts the level
interrupt sent by the PID. The RIRR bit is reset when an EOI message is
received from the local (x)APIC.
POLARITY This bit specifies the polarity of each interrupt signal connected to the interrupt
pins of the PID. A value of 0 means the signal is high-active and a value of 1
means the signal is low-active. In the case of level, high-active means if the pin
is sampled high, it is considered active. In the case of an edge, high-active
means the low-to-high edge is considered active.
DELIVERY This bit is read-only. It holds the current status of interrupt delivery to the
STATUS processor. This bit functions differently depending on the Trigger Mode bit.
When the Trigger Mode bit indicates edge sensitive:
The Delivery Status bit is set when an active edge is detected on the interrupt
pin.
The Delivery Status bit is reset when the interrupt message is successfully sent
to the processor.
When the Trigger Mode bit indicates level sensitive:
The Delivery Status bit reflects the assertion of the pin. i.e. If the pin is at its
active level, according to its Polarity bit, the Delivery Status bit is set; If the pin
is at its inactive level, according to its Polarity bit, the Delivery status bit is
reset.
To accurately determine the delivery status of an interrupt in level mode the
RIRR bit must be considered as well as the Delivery Status bit.
Register Descriptions
Description
2-51