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9–2 Alpha Architecture Handbook
CHME Change mode to executive
The CHME instruction allows a process to change its mode in a controlled
manner. A change in mode also results in a change of stack pointers: the old
pointer is saved, the new pointer is loaded. Registers R2..R7, PS, and PC are
pushed onto the selected stack. The saved PC addresses the instruction fol-
lowing the CHME instruction. The value in R16 specifies the particular
exception type.
CHMK Change mode to kernel
CHMK allows a process to change its mode to kernel in a controlled manner.
A change in mode also results in a change of stack pointers: the old pointer is
saved, the new pointer is loaded. R2..R7, PS, and PC are pushed onto the ker-
nel stack. The saved PC addresses the instruction following the CHMK
instruction. The value in R16 specifies the particular exception type.
CHMS Change mode to supervisor
CHMS allows a process to change its mode in a controlled manner. A change
in mode also results in a change of stack pointers: the old pointer is saved, the
new pointer is loaded. R2..R7, PS, and PC are pushed onto the selected stack.
The saved PC addresses the instruction following the CHMS instruction. The
value in R16 specifies the particular exception type.
CHMU Change mode to user
CHMU allows a process to call a routine via the change mode mecha-
nism.R2..R7, PS, and PC are pushed onto the current stack. The saved PC
addresses the instruction following the CHMU instruction. The value in R16
specifies the particular exception type.
CLRFEN Clear floating-point enable
CLRFEN writes a zero to the floating-point enable register.
GENTRAP Generate trap
GENTRAP is provided for reporting runtime software conditions. It switches
the processor to kernel mode and pushes registers R2..R7, the updated PC,
and the PS on the kernel stack. It then dispatches to the address of the GEN-
TRAP vector, stored in a control block.
Table 9–1 : Unprivileged OpenVMS Alpha PALcode Instruction Summary (Continued)
Mnemonic Operation and Description