STM8S datasheet(64/467 Pages) STMICROELECTRONICS

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Interrupt controller (ITC)

RM0016

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moments in order to execute a specific task. Some of these recurring tasks are short

enough to be treated directly in an ISR (interrupt service routine), rather than going back to

the main program. To cover this case, you can set the AL bit before entering Low power

mode (by executing WFI instruction), then the interrupt routine returns directly to Low power

mode. The run time/ISR execution is reduced due to the fact that the register context is

saved only on the first interrupt.

As a consequence, all the operations can be executed in ISR in very simple applications. In

more complex ones, an interrupt routine may relaunch the main program by simply resetting

the AL bit.

For example, an application may need to be woken up by the auto-wakeup unit (AWU)

every 50 ms in order to check the status of some pins/sensors/push-buttons. Most of the

time, as these pins are not active, the MCU can return to Low power mode without running

the main program. If one of these pins is active, the ISR decides to launch the main program

by resetting the AL bit.

6.5

Concurrent and nested interrupt management

STM8 devices feature two interrupt management modes:

•

Concurrent mode

•

Nested mode

6.5.1

Concurrent interrupt management mode

In this mode, all interrupts are interrupt priority level 3 so that none of them can be

interrupted, except by a TLI, RESET, or TRAP.

The hardware priority is given in the following order from the lowest to the highest priority,

that is: MAIN, IT4, IT3, IT2, IT1, IT0, TRAP/TLI (same priority), and RESET.

Figure 15 shows an example of concurrent interrupt management mode.

Figure 15. Concurrent interrupt management

MSv47717V2

Software

priority level

3/0

11/10

RIM

TRAP

IT0

IT3

IT4

IT2

IT1

Main

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