Specifications

C–2 SROM Initialization
Subject to Change – 17 January 1997
Firmware Interface
10. Copy the contents of the system flash ROM to memory and begin code execu-
tion.
11. Pass parameters up to the next level of firmware to provide a predictable firm-
ware interface.
C.2 Firmware Interface
A firmware interface provides a mechanism for passing critical information about
the state of the system and CPU up to the next level of firmware. This interface is
achieved through the use of a set of defined SROM output parameters as described in
Table C–1.
This specific firmware interface serves the 21164 microprocessor. Other Alpha
microprocessor implementations require a different firmware interface.
Table C–1 Output Parameter Descriptions
Output Parameter Parameter Description
r1 (t0)—BC_CONTROL
value
The BC_CONTROL value allows the next-level software
to preserve any system-specific Bcache configuration
information.
r2 (t1)—BC_CONFIG value The BC_CONFIG value preserves the Bcache
configuration information such as size and read/write
speed.
r3 (t2)—BC_CONFIG_OFF
value
The BC_CONFIG value for turning the Bcache off (if
necessary). This value may be harder to be determined by
the next level of firmware, so the SROM computes it and
passes it up.
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 is sufficient
for simple systems. Systems that need to communicate
more detailed memory configuration can do so through the
system context value (see last entry in this table).
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). This may be a multiple of the actual
internal cycle count of the microprocessor as specified in
the
Alpha AXP 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).