T-Kernel Specification (1.B0.02)

252 CHAPTER 5. T-KERNEL/SM
5.6 Power Management Functions
Power management functions are called from T-Kernel/OS. See tk set pow.
The manner of calling these functions is implementation-dependent. Simple system calls are possible,
as is the use of a trap. Use of an extended SVC or other means that makes use of OS functions is not
possible, however. Providing these functions in T-Monitor is another option.
The specifications given here for low pow and off pow are reference specifications. Since these functions
are used only inside T-Kernel, other specifications may be devised as well. It is even possible to
design completely different specifications in order to realize more advanced power-saving features. If the
functionality is similar to that specified here, however, it would be best to follow these specifications as
closely as practical.
• void low_pow( void )
Switches to low-power mode and waits for an interrupt to be raised. This function is called from
the task dispatcher, and performs the following processing.
(A) Goes to low-power mode.
(B) Waits for an external interrupt to be raised.
(C) When an external interrupt is raised, restores normal power mode and returns to its caller.
This function is called in interrupts disabled state. Interrupts must not be enabled. The speed of
response to an interrupt affects processing speed, and should be as fast as possible.
• void off_pow( void )
Suspends the system. When a resume factor occurs, it resumes system operation.
This function is called from tk set pow, and performs the following processing.
(A) Puts the hardware in suspended state.
(B) Waits for a resume factor to occur.
(C) When a resume factor occurs, returns from suspended state and returns to its caller.
This function is called in interrupts disabled state. Interrupts must not be enabled. The device
drivers perform the suspending and resuming of peripherals and other devices.
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T-Kernel 1.B0.02