Specifications

17 January 1997 – Subject to Change
SROM Initialization C–3
Automatic CPU Speed Detection
C.3 Automatic CPU Speed Detection
The AlphaPC 164 TOY clock detects the speed of the CPU. This allows a somewhat
generic SROM to support AlphaPC 164 systems configured for different CPU
speeds. The speed is determined by counting CPU cycles between TOY clock
interrupts that are set to occur at known time intervals (1/8 second).
r19 (a3)—Signature and
system revision ID
This register includes a signature that specifies that the
transfer is following the standard protocol and that the
other values can be trusted. In addition, the signature can
identify which version of the protocol is being followed.
The system revision is a 16-bit field that communicates
system revisions that would be significant to operating
system software. The register has the following format:
Bits <63:32> = Ignore
Bits <31:16> = Signature
Bits <15:0> = System Revision
Valid signatures have the following values:
0xdeca–V1 (previous version of this specification)
0xdecb–V2 (current version of this specification)
r20 (a4)—Active processor
mask
The processor mask identifies each processor that is
present on the current system. Each mask bit corresponds
to a processor number associated by the bit number (for
example, bit 0 corresponds to processor 0). A value of 1 in
the mask indicates that the processor is present, a value of 0
indicates that the processor is not present.
To qualify as present a processor must be:
•
Physically present
•
Functioning normally
•
Capable of sending and receiving interprocessor
interrupt requests
Uniprocessor systems pass a value of 1 to this register.
r21 (a5)—System context
value
The context value is interpreted in a system-specific
manner. If the system needs to pass more than one system-
specific parameter, then it may pass a context value. A
context value is a physical address pointer to a data
structure of many system-specific values.
Table C–1 (Continued) Output Parameter Descriptions
Output Parameter Parameter Description