6 conga Tech Notes
The conga-X945/XA945 has some technological features that require additional
explanation. The following section will give the reader a better understanding of some of
these features. This information will also help to gain a better understanding of the
information found in the System Resources section of this user's guide as well as some
of the setup nodes found in the BIOS Setup Program description section.
6.1 Comparison of I/O APIC to 8259 PIC Interrupt mode
I/O APIC (Advanced Programmable Interrupt controller) mode deals with interrupts
differently than the 8259 PIC.
The method of interrupt transmission used by APIC mode is implemented by
transmitting interrupts through the system bus and they are handled without the
requirement of the processor to perform an interrupt acknowledge cycle.
Another difference between I/O APIC and 8259 PIC is the way the interrupt numbers
are prioritized. Unlike the 8259 PIC, the I/O APIC interrupt priority is independent of the
actual interrupt number.
A major advantage of the I/O APIC found in the chipset of the conga-X945/XA945 is
that it's able to provide more interrupts, a total of 24 to be exact. It must be mentioned
that the APIC is not supported by all operating systems. In order to utilize the APIC
mode it must be enabled in the BIOS setup program before the installation of the OS
and it only functions in ACPI mode. You can find more information about APIC in the IA-
32 Intel Architecture Software Developer's Manual, Volume 3 in chapter 8.
Note
You must ensure that your operating system supports APIC mode in order to use it.
6.2 Native vs. Compatible IDE mode
6.2.1 Compatible Mode
When operating in compatible mode, the SATA and PATA (Parallel ATA) controller
together need two legacy IRQs (14 and 15) and are unable to share these IRQs with
other devices. This is a result of the fact that the SATA and PATA controller emulate
legacy IDE controllers.
6.2.2 Native Mode
Native mode allows the SATA and PATA controllers to operate as true PCI devices and
therefore do not need dedicated legacy resources, which means it can be configured
anywhere within the system. When either the SATA or PATA controller runs in native
mode it only requires one PCI interrupt for both channels and also has the ability to
share this interrupt with other devices in the system. Setting Enhanced mode in the
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