T-Kernel Specification (1.B0.02)

4.9. SYSTEM MANAGEMENT FUNCTIONS 199
tk set pow
Set Power Mode
[C Language Interface]
ER ercd = tk_set_pow ( UINT powmode ) ;
[Parameters]
UINT powmod Low-power mode
[Return Parameters]
ER ercd Error code
[Error Codes]
E OK Normal completion
E PAR Parameter error (value that cannot be used in powmode)
E QOVR Low-power mode disable count overflow
E OBJ TPW ENALOWPOW was requested with low-power mode disable count at 0
[Description]
The following two power-saving functions are supported.
• Switching to low-power mode when the system is idle
When there are no tasks to be executed, the system switches to a low-power mode provided in
hardware. Low-power mode is a function for reducing power use during very short intervals, such
as from one timer interrupt to the next. This is accomplished, for example, by lowering the CPU
clock frequency. It does not require complicated mode-switching in software but is implemented
mainly using hardware functionality.
• Automatic power-off
When the operator performs no operations for a certain length of time, the system automatically
cuts the power and goes to suspended state. If there is a start request (interrupt, etc.) from a
peripheral device or if the operator turns on the power, the system resumes from the state when
the power was cut. In the case of a power supply problem such as low battery, the system likewise
cuts the power and goes to suspended state.
In suspended state, the power is cut to peripheral devices and circuits as well as to the CPU, but
the main memory contents are retained.
tk set pow sets the low-power mode.
powmode:= ( TPW_DOSUSPEND || TPW_DISLOWPOW || TPW_ENALOWPOW )
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T-Kernel 1.B0.02