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4.3.2 Saving and Restoring the Accumulator in the ISRs

The interrupt functions generated by the RX compiler with

#pragma vector

do not preserve the RX

accumulator register, unless the compiler option

-save_acc

is activated. This can be achieved in the

HEW IDE by selecting the menu Build | RX Standard Toolchain, the CPU tab, Details... button (see

Figure 11).

NOTE: When using the Vanilla kernel, you need to save and restore the accumulator register if the

ISR body can clobber it somehow, for example by performing one of the MAC instructions or a

floating-point instruction.

4.3.3 Specifying the Stacks (stacksct.h header file)

As described before, the QP framework uses exclusively the Supervisor stack and does not use the User

Stack at all. In the Renesas compiler the sizes of the stacks and heap are specified by means of

#pragma

stacksize

directives, which traditionally are placed in the

stacksct.h

header file. The

#pragma

stacksize si

specifies the Supervisor.

Listing 7: Specifying stack size int stacksct.h

#pragma stacksize si=256

4.3.4 Idle loop customization in the Vanilla port

As described in Chapter 7 of [PSiCC2], when no events are available, the non-preemptive Vanilla

scheduler invokes the platform-specific callback function

QF_onIdle()

, which you can use to save CPU

power, or perform any other idle processing (such as Q-SPY software trace output).

NOTE: The idle callback

QF_onIdle()

must be invoked with interrupts disabled, because the idle

condition can be changed by any interrupt that posts events to event queues.

QF_onIdle()

must

internally unlock interrupts, ideally atomically with putting the CPU to the power-saving mode (see

also Chapter 7 in [PSiCC2]).

Listing 8: Idle callback QF_onIdle() for the Vanilla kernel in bsp.c

(1) void QF::onIdle(void) { // entered with interrupts DISABLED

(2) BSP_LED_IDLE_ON(); // toggle the User LED on and then off, see NOTE02

(3) BSP_LED_IDLE_OFF();

(4) #ifdef Q_SPY

. . .

(5) #elif defined NDEBUG

(6) __wait_for_interrupt();

(7) #else

(8) QF_INT_ENABLE();

#endif

}

(1) This routine is always entered with interrupts disabled to avoid a race condition with interrupts that

could post one or more events to active objects and thus invalidate the idle condition.

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