AngoLinux

80386 Programmer's Reference Manual -- Opcode CLTS

CLTS -- Clear Task-Switched Flag in CR0

Opcode	Instruction	Clocks	Description	Example
OF 06	clts	5	Clear task-switched flag	`clts`

Operation




TS Flag in CR0 := 0;

Description

CLTS clears the task-switched (TS) flag in register CR0. This flag is set by the 80386 every time a task switch occurs. The TS flag is used to manage processor extensions as follows:

Every execution of an ESC instruction is trapped if the TS flag is set.
Execution of a WAIT instruction is trapped if the MP flag and the TS flag are both set.

Thus, if a task switch was made after an ESC instruction was begun, the processor extension's context may need to be saved before a new ESC instruction can be issued. The fault handler saves the context and resets the TS flag.

CLTS appears in operating system software, not in application programs. It is a privileged instruction that can only be executed at privilege level 0.

Flags Affected

TS := 0 (TS is in CR0, not the flag register)

Protected Mode Exceptions

#GP(0) if CLTS is executed with a current privilege level other than 0

Real Address Mode Exceptions

None (valid in Real Address Mode to allow initialization for Protected Mode)

Virtual 8086 Mode Exceptions

Same exceptions as in Real Address Mode

[Home Page dell'ITIS "Fermi"] [80386 Programmer's Reference Manual Index] [Previous] [Next]