Intel 80286, 80287 manual CLTS-Clear Task Switched Flag, Opcode Instruction ClocksDescription

THE 80286 INSTRUCTION SET

CLTS-Clear Task Switched Flag

Opcode Instruction ClocksDescription

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 CLTS 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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