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E
VID3-VID0
On-Board
VR
4
Figure 53. Upgrade Presence
Detect Schematic—Case 3
8.3.3.
BIOS CONSIDERATIONS
Please refer to the Pentium
Developers
Manual:
Volume
Reference Manual (Order Number 242691) for BIOS
requirements.
It is the responsibility of the BIOS to detect the type
of CPU in the system and program the support
hardware accordingly. In most cases, the BIOS does
this by reading the CPU signature, comparing it to
known signatures, and, upon finding a match,
executing the corresponding hardware initialization
code.
The CPUID instruction is used to determine several
processor parameters. Following execution of the
CPUID instruction, bits 12 and 13 of the EAX register
can be used to determine if the processor is an OEM
or an OverDrive processor. An OverDrive processor
is present if bit 13=0 and bit 12=1.
NOTE
Contact your BIOS vendor to ensure that the
above requirements have been included.
OverDrive ® Processor CPUID
8.3.3.1.
Following
power-on
RESET
instruction, the EAX register contains the values
shown in Table 32.
PENTIUM® PRO PROCESSOR AT 150, 166, 180, and 200 MHz
Socket 8
8.3.3.2.
CPU signature detection has been a common cause
of current upgradability problems due to BIOS. A few
precautions within the BIOS can help to eliminate
future upgradability problems with Pentium Pro
processor-based systems. When programming or
modifying a BIOS, be aware of the impact of future
OverDrive
recommendations should prevent problems in the
future:
®
Pro Processor
3,
Programmer's
•
•
•
•
•
•
8.4.
or
the
CPUID
This section describes the electrical requirements for
the OverDrive processor.
Table 32. OverDrive
®
Processor CPUID
Type
Family
Model
[13:12]
[11:8]
[7:4]
1
6
Common Causes of Upgradability
Problems Due to BIOS
processors.
Always use the CPU signature and feature flags
to identify the processor, including future
processors.
Never use timing loops for delays.
If an OverDrive processor is detected, report
the presence of an "OverDrive processor" to the
end-user.
If an OverDrive processor is detected, don't test
on-chip cache sizes or organization. The
OverDrive processor cache parameters differ
from those of the Pentium Pro processor.
If an OverDrive processor is detected, don't use
the Pentium Pro processor model specific
registers
and
test
processor MSRs differ from those of the
Pentium Pro processor.
MTRRs must be programmed as a Pentium Pro
processor.
OverDrive
®
Processor
Electrical Specifications
Stepping
[3:0]
3
X
The
following
registers.
OverDrive
87
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