Renesas R8C/17 Manual de usuario descargar pdf (Pagina 15)

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R8C/Tau-NC30

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3.4 QP Idle Loop Customization in QF_onIdle()

The cooperative “vanilla” kernel can very easily detect the situation when no events are available,

in which case

QF_run()

calls the

QF_onIdle()

callback. You can use

QF_onIdle()

to suspended the

CPU to save power, if your CPU supports such a power-saving mode. Please note that

QF_onIdle()

is called repetitively from the event loop whenever the event loop has no more events to process,

in which case only an interrupt can provide new events. The

QF_onIdle()

callback is called with in-

terrupts locked, because the determination of the idle condition might change by any interrupt

posting an event.

M16C/R8C microcontrollers support several power-saving levels (consult the specific data sheet for

details). The following piece of code shows the

QF_onIdle()

callback that puts M16C/R8C into the

idle power-saving mode. Please note that M16C/R8C architecture allows for very atomic setting

the low-power mode and enabling interrupts at the same time (see the article “Using Low-Power

Modes in Foreground/Background Systems” [Samek 07a]).

(1) void QF_onIdle(void) {

#ifdef Q_SPY

/* perform QS trace output via R8C UART... */

. . .

(2) #elif (defined NDEBUG) /* low-power mode interferes with debugging */

(3) /* stop all peripheral clocks that you can in your applicaiton ... */

(4) _asm("FSET I"); /* NOTE: the following WAIT instruction will */

(5) _asm("WAIT"); /* execute before entering any pending interrupt */

#else

(6) QF_INT_UNLOCK(); /* just unlock interrupts */

#endif

}

Listing 5

QF_onIdle()

for the non-preemptive (“vanilla”) QP port to M16C/R8C.

(1) The

QF_onIdle()

callback is always called with interrupts locked to prevent any race condition

between posting events from ISRs and transitioning to the sleep mode.

(2) The low-power mode is entered only in the Release (not DEBUG) configuration.

(3) The clock management

s are setup the desired sleep mode. Please note that the sleep

mode is not active until the SLEEP command.

(4) The interrupts are unlocked with the

FSET I

instruction.

(5) The sleep mode is activated with the

WAIT

instruction.

NOTE: As described in “M16C/60, M16C/20 Series Software Manual”, Section 5.2.1 “Interrupt

Enable Flag”, the instruction immediately following the

FSET I

instruction, will be executed be-

fore any pending interrupt. This guarantees atomic transition to the WAIT mode.

CAUTION: The instruction pair (

FSET I, WAIT

) should never be separated by any other instruc-

tion.

(6) In the DEBUG configuration the interrupts are simply unlocked.

NOTE: Every path through

QF_onIdle()

callback function must ultimately unlock interrupts.

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