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10-68 Vol. 3
ADVANCED PROGRAMMABLE INTERRUPT CONTROLLER (APIC)
Reserved fields are not assumed to be any value. Software must preserve their
contents on writes. Other fields in the Message Data Register are described below.
1. Vector — This 8-bit field contains the interrupt vector associated with the
message. Values range from 010H to 0FEH. Software must guarantee that the
field is not programmed with vector 00H to 0FH.
2. Delivery Mode — This 3-bit field specifies how the interrupt receipt is handled.
Delivery Modes operate only in conjunction with specified Trigger Modes. Correct
Trigger Modes must be guaranteed by software. Restrictions are indicated below:
a. 000B (Fixed Mode) — Deliver the signal to all the agents listed in the
destination. The Trigger Mode for fixed delivery mode can be edge or level.
b. 001B (Lowest Priority) — Deliver the signal to the agent that is executing
at the lowest priority of all agents listed in the destination field. The trigger
mode can be edge or level.
c. 010B (System Management Interrupt or SMI) — The delivery mode is
edge only. For systems that rely on SMI semantics, the vector field is ignored
but must be programmed to all zeroes for future compatibility.
d. 100B (NMI) — Deliver the signal to all the agents listed in the destination
field. The vector information is ignored. NMI is an edge triggered interrupt
regardless of the Trigger Mode Setting.
e. 101B (INIT) — Deliver this signal to all the agents listed in the destination
field. The vector information is ignored. INIT is an edge triggered interrupt
regardless of the Trigger Mode Setting.
f. 111B (ExtINT) — Deliver the signal to the INTR signal of all agents in the
destination field (as an interrupt that originated from an 8259A compatible
interrupt controller). The vector is supplied by the INTA cycle issued by the
activation of the ExtINT. ExtINT is an edge triggered interrupt.
3. Level — Edge triggered interrupt messages are always interpreted as assert
messages. For edge triggered interrupts this field is not used. For level triggered
interrupts, this bit reflects the state of the interrupt input.
4. Trigger Mode — This field indicates the signal type that will trigger a message.
a. 0 — Indicates edge sensitive.
b. 1 — Indicates level sensitive.