10.4
PCI Bus Resource Management
The bus structure of the PP 110/01x is quite complex. There are two on-board PCI busses: a
64-bit bus which connects to the Ethernet controller, the PMC sites and the CompactPCI bridge
chip, and a second 32-bit bus which connects to the remaining on-board peripherals (CSB5,
graphics). Associated with these busses are a number of interrupt lines.
The 32-bit bus operates at 33MHz with 3.3V signaling levels. The 64-bit bus can operate at
33MHz with either 3.3V or 5V signaling levels. It normally runs at 66MHz, but may be slowed to
33MHz if a 5V only or 33MHz PMC module is fitted.
10.4.1 PCI Resource Allocation
The PC BIOS initializes all devices on the local PCI bus, and allocates appropriate memory
address ranges, I/O address ranges, and interrupt routings for all these devices. This process is
automatic as part of the BIOS “Plug-and-play” setup. When the board is System Controller it will
also allocate memory, I/O or interrupt resources to devices found on the CompactPCI bus. The
ServerWorks chipset allows for a flexible allocation of many PCI bus interrupts to the available
interrupt inputs on the PC-compatible interrupt controllers provided on the board. The PC BIOS
uses this feature to program default settings which it considers appropriate for the combination
of on-board devices and any device fitted to the PMC site. In some configurations, depending on
the operating system being used and the capability of the relevant device drivers, it may be
necessary for the user to modify this default configuration, to minimize the sharing of interrupt
lines. The PC BIOS Setup screen for
Advanced | PCI Device Configuration
allows
this.
This screen allows the user to override the PC BIOS default selections for interrupt allocation,
but care must be taken when doing this to avoid conflicts which may result in operating system
or even BIOS “crashes”. To allow maximum flexibility of choice for the user, the PC BIOS
performs limited checks on the user’s interrupt allocation. In the event that there is a problem, it
may be necessary to clear the CMOS memory (see Section 2.7), or even to reset the Extended
System Configuration Data via the
Reset Configuration Data
field of the BIOS Setup
screen for
Advanced
configuration settings. The PC BIOS does not allow the user to override
the allocation of memory and I/O address ranges.
NOTE
When reallocating interrupts using the BIOS Setup screens, try to avoid allocating
the PMC interrupts to ones also allocated to other devices. This sharing of
interrupts can cause problems with some operating systems where device drivers
do not correctly handle shared interrupts.
PC BIOS
PP 110/01x
10-5
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