Instruction manual

14.5.3 Halt
The console (halt) program interprets commands entered at the console terminal
and controls the operation of the main processor. Through the console terminal,
an operator can boot the operating system, a field technician can maintain the
system, and a system user can communicate with running programs.
The processor can halt as the result of an operator command, a serious system
error, a HALT instruction, or a boot failure. The operator might put the system
in an inconsistent state through the use of console commands. The operation of
the processor in such a state is undefined.
(Section 16.4.15 discusses console security.)
Program mode (also called program I/O mode) operation of the system is the
normal operating mode. However, the operating mode may be set to console mode
(also called halt mode) by one of the following methods:
• Kernel Mode HALT
When the system is running in kernel program mode, the HALT instruction
is issued and the default recovery action is specified to be Halt. If the default
recovery action is set for Boot/Halt, the console mode is entered on a failure of
the boot operation. If the default recovery action is set for Restart/Boot/Halt,
then console mode is entered on failure of both the restart and the boot
operations.
• Severe Corruption of Operating Environment
The CPU forces a processor restart when it detects one of several events
which it considers to be a severe corruption of its operating environment. The
system firmware treats this like a processor restart caused by a kernel mode
HALT, as described above. Table 49 defines the processor restart codes.
14–12 Powerup Initialization and Firmware Entry