Maskable interrupt sources

Maskable interrupt vector sources are serviced if the corresponding interrupt is enabled and if its own interrupt software priority in ITC_SPRx registers is higher than the one currently being serviced (I1 and I0 in CCR register). If one of these two conditions is not met, the interrupt is latched and remains pending.

●External interrupts

External interrupts can be used to wake up the MCU from Halt mode. The device sensitivity to external interrupts can be selected by software through the External Interrupt Control registers (EXTI_CRx).

When several input pins connected to the same interrupt line are selected simultaneously, they are logically ORed.

When external level-triggered interrupts are latched, if the given level is still present at the end of the interrupt routine, the interrupt remains activated except if it has been inactivated in the routine.

●Peripheral interrupts

Most peripheral interrupts cause the MCU to wake up from Halt mode. See the interrupt vector table in the datasheet.

A peripheral interrupt occurs when a specific flag is set in the peripheral status register and the corresponding enable bit is set in the peripheral control register.

The standard sequence for clearing a peripheral interrupt performs an access to the status register followed by a read or write to an associated register. The clearing sequence resets the internal latch. A pending interrupt (that is an interrupt waiting to be serviced) is therefore lost when the clear sequence is executed.

6.3Interrupts and low power modes

All interrupts allow the processor to exit from Wait mode.

Only external and other specific interrupts allow the processor to exit from Halt and Activehalt mode (see wakeup from halt and wakeup from Active-halt in the interrupt vector table in the datasheet).

When several pending interrupts are present while waking up from Halt mode, the first interrupt serviced can only be an interrupt with exit-from-Halt mode capability. It is selected through the decision process shown in Figure 14. If the highest priority pending interrupt cannot wake up the device from Halt mode, it will be serviced next.

If any internal or external interrupt (from a timer for example) occurs while the HALT instruction is executing, the HALT instruction is completed but the interrupt invokes the wakeup process immediately after the HALT instruction has finished executing. In this case the MCU is actually waking up from Halt mode to Run mode, with the corresponding delay of tWUH as specified in the datasheet.

6.4Activation level/low power mode control

The MCU activation level is configured by programming the AL bit in the CFG_GCR register (see global configuration register (CFG_GCR)).

This bit is used to control the low power modes of the MCU. In very low power applications, the MCU spends most of the time in WFI and is woken up (through interrupts) at specific