3-70
INSTRUCTION SET REFERENCE
CLTS—Clear Task-Switched Flag in CR0
Description
This instruction clears the task-switched (TS) flag in the CR0 register. This instruction is
intended for use in operating-system procedures. It is a privileged instruction that can only be
executed at a CPL of 0. It is allowed to be executed in real-address mode to allow initialization
for protected mode.
The processor sets the TS flag every time a task switch occurs. The flag is used to synchronize
the saving of FPU context in multitasking applications. Refer to the description of the TS flag
in Section 2.5., Control Registers in Chapter 2, System Architecture Overview of the Intel Archi-
tecture Software DeveloperÂ’s Manual, Volume 3, for more information about this flag.
Operation
CR0(TS)
<
0;
Flags Affected
The TS flag in CR0 register is cleared.
Protected Mode Exceptions
#GP(0)
If the CPL is greater than 0.
Real-Address Mode Exceptions
None.
Virtual-8086 Mode Exceptions
#GP(0)
If the CPL is greater than 0.
Opcode
Instruction
Description
0F 06
CLTS
Clears TS flag in CR0
