Compaq ECQD2KCTE manual Chme, Chmk, Chms, Chmu, Clrfen

Models: ECQD2KCTE

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Table 9–1 : Unprivileged OpenVMS Alpha PALcode Instruction Summary (Continued)

Mnemonic

Operation and Description

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.

9–2Alpha Architecture Handbook

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Compaq ECQD2KCTE manual Chme, Chmk, Chms, Chmu, Clrfen