User`s guide

Table B–1 (Cont.) Output Parameter Descriptions
Output Parameter Parameter Description
r17 (a1) - Memory size This value is an unsigned quadword count of the number
of contiguous bytes of good memory in the system starting
at physical address zero. This simple mechanism will
be sufficient for simple systems. Systems that need to
communicate more detailed memory configuration may do
so through the system context value (see last table entry).
r18 (a2) - Cycle count in
picoseconds
This value is the number of picoseconds that elapse for each
increment of the processor cycle count (as read by the RPCC
instruction). Note that this may be a multiple of the actual
internal cycle count of the microprocessor as specified in the
Alpha Architecture Reference Manual. (A microprocessor
will increment the processor cycle count a multiple of the
microprocessor clock where the multiple is a power of 2,
including 2
0
= 1.)
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:
<63..32> Don’t care
<31..16> Signature
<15..0> System revision
Valid signatures have the following values:
deca - V1 (previous version of this specification)
decb - V2 (current version of this specification)
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SROM Initialization B–3