System Debug provides a large collection of predefined environment
variables, the names of which are reserved and may not be
replaced by user-defined variables with the VAR and LOC commands.
Several environment variables provide access to the current
System Debug execution environment. Examples of these variables
include the current input radix and the prompt string. Other environment
variables are used to access key components of the state of the machine
being examined. For example, all of the machine registers defined
in the HP 3000 and HP Precision Architectures are available as environment
variables. Subject to the context of use, some of these variables
may be set by the user with the ENV command. The environment variables that correspond
to the CM and NM machine registers are also accessible through the MR (modify register) and DR (display register) commands. All environment variables
may be read (accessed) as expression operands. Some environment variables
also require privileged mode for modification access.
The ENV command in chapter 4 gives a detailed description
of each of the predefined environment variables and specifies which
ones may be modified and which ones are read-only.