Intel C2518 FH8065501516710 数据表
产品代码
FH8065501516710
Volume 2—8259 Programmable Interrupt Controller (PIC)—C2000 Product Family
Operation
Intel
®
Atom™ Processor C2000 Product Family for Microserver
Datasheet, Vol. 2 of 3
September 2014
554
Order Number: 330061-002US
29.3
Operation
29.3.1
Fully-Nested Mode
In this mode, interrupt requests are ordered in priority from 0 through 7, with 0 being
the highest. When an interrupt is acknowledged, the highest priority request is
determined and its vector placed on the bus. Additionally, the ISR for the interrupt is
set. This ISR bit remains set until: the processor issues an EOI command immediately
before returning from the service routine or if in AEOI mode, on the trailing edge of the
second INTA#. While the ISR bit is set, all further interrupts of the same or lower
priority are inhibited, while higher levels generate another interrupt. Interrupt priorities
are changed in the rotating priority mode.
29.3.2
Special Fully-Nested Mode
This mode is used in the case of a system where cascading is used, and the priority has
to be conserved within each slave. In this case, the special fully-nested mode is
programmed to the master controller. This mode is similar to the fully-nested mode
with the following exceptions:
• When an interrupt request from a certain slave is in service, this slave is not locked
out from the master priority logic, and further interrupt requests from higher
priority interrupts within the slave are recognized by the master and initiate the
interrupts to the processor. In the normal-nested mode, a slave is masked out
when its request is in service.
• When exiting the interrupt service routine, the software has to check whether the
interrupt serviced was the only one from that slave. This is done by sending a Non-
specific EOI command to the slave and then reading its ISR. If it is 0, a non-specific
EOI is also sent to the master.
29.3.3
Automatic Rotation Mode (Equal Priority Devices)
In some applications, there are a number of interrupting devices of equal priority. The
automatic rotation mode provides for a sequential eight-way rotation. In this mode, a
device receives the lowest priority after being serviced. In the worst case, a device
requesting an interrupt has to wait until each of the seven other devices are serviced at
most once.
Two ways to accomplish automatic rotation using OCW2.REOI are: the rotation on the
Non-specific EOI command (OCW2.REOI=101b) and the rotation in the automatic EOI
mode which is set by (OCW2.REOI=100b).
29.3.4
Specific Rotation Mode (Specific Priority)
The software changes the interrupt priorities by programming the bottom priority. For
example, if IRQ5 is programmed as the bottom priority device, then IRQ6 is the highest
priority device. The Set Priority command is issued in OCW2 to accomplish this, where
OCW2.REOI=11xb, and OCW2.ILS is the binary priority level code of the bottom
priority device.
In this mode, the internal status is updated by the software control during OCW2.
However, it is independent of the EOI command. Priority changes are executed during
an EOI command by using the Rotate-on-Specific EOI command in OCW2
(OCW2.REOI=111b) and OCW2.ILS=IRQ level to receive bottom priority.