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6–4 Alpha Architecture Handbook
PALcode should be written modularly to facilitate the easy replacement or conditional build-
ing of each component. Such a practice simplifies the integration of CPU hardware, system
platform hardware, console firmware, operating system software, and compilers.
PALcode subsections that are commonly subject to modification include:
• Translation Buffer fill
• Process structure and context switch
• Interrupt and exception frame format and routine dispatch
• Privileged PALcode instructions
• Transitions to and from console I/O mode
• Power-up reset
6.7 Required PALcode Instructions
The PALcode instructions listed in Table 6–1 and Section C.11 must be recognized by mne-
monic and opcode in all operating system implementations, but the effect of each instruction is
dependent on the implementation. Compaq defines the operation of these PALcode instruc-
tions for operating system implementations supplied by Compaq.
Table 6–1: PALcode Instructions that Require Recognition
Mnemonic Name
BPT Breakpoint trap
BUGCHK Bugcheck trap
CSERVE Console service
GENTRAP Generate trap
RDUNIQUE Read unique value
SWPPAL Swap PALcode
WRUNIQUE Write unique value