ST STM8S Reference Manual

RM0016 Interrupt controller (ITC)
Doc ID 14587 Rev 8 63/449
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
MAIN
IT4
IT2
IT1
TRAP
IT1
MAIN
IT0
I1
HARDWARE PRIORITY
SOFTWARE
3
3
3
3
3
3/0
3
11
11
11
11
11
11 / 10
11
RIM
IT2 IT1 IT4
TRAP
IT3 IT0
IT3
I0
10
PRIORITY
LEVEL
USED STACK = 10 BYTES

ST STM8S Specifications

General

Brand	ST
Model	STM8S
Category	Microcontrollers
Language	English