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THE
80286
INSTRUCTION
SET
CLTS-Clear
Task Switched
Flag
Opcode
Instruction
Clocks Description
OF
06 CLTS
2 Clear task switched flag
FLAGS
MODIFIED
Task switched=O
FLAGS
UNDEFINED
None
OPERATION
CLTS clears the task switched flag in the Machine Status Word. This flag
is
set by the 80286 every
time a task switch occurs. The TS flag
is
used to manage processor extensions as
follows:
every execu-
tion of a WAIT or an ESC instruction
will
be trapped if the
MP
flag of MSW
is
set and the task
switched flag
is
set. Thus,
if
a processor extension
is
present and a task switch has been made since the
last
ESC
instruction
was
begun, the processor extension's context must be saved before a
new
instruc-
tion can be issued. The fault routine
will
save the context and reset the task switched flag
or
place the
task requesting the processor extension into a queue until the current processor extension instruction
is
completed.
CLTS appears in operating systems software, not in applications programs.
It
is
a privileged instruction
that
can only be executed
at
level
O.
PROTECTED
MODE
EXCEPTIONS
#GP(O) if
CL
TS
is
executed with a current privilege level other than
o.
REAL
ADDRESS
MODE
EXCEPTIONS
None (valid in REAL ADDRESS MODE to allow power-up initialization for Protected Mode) ,
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