Software description

AN3265

12/19

Doc ID 17860 Rev 1

2.3.2

Interrupt function flowcharts

Port B interrupt function handler

This interrupt routine is associated to button1. It is called when the user presses button (see

Table 2).

Clock interrupt function handler

This interrupt routine is called when a failure is detected on the HSE clock used as master

clock (see Table 2).

2.3.3

State machine flowchart

The State_Machine() function implements the algorithm that controls the progress of the

application execution according to external events.

1.

SystemState = 0

LD2 blinks. The application is ready to demonstrate how to use the WWDG:

a)

The first time Button1 is pressed, an interrupt is triggered and the ButtonPressed

flag is set (see Section : Port B interrupt function handler). As a result, the

execution time is lengthened. This is signalled by LD2 blinking at a slower rate

since the Dly parameter which controls the delay between each WWDG refresh is

incremented.

b)

The second time Button1 is pressed, the delay introduced by Dly becomes too

long to refresh the WWDG counter in time. The STM8S105C6T6 is then reset by

the WWDG. Just before the reset, SystemState variable is saved in the data

EEPROM. This shows how to use the data EEPROM for data saving (see

Section 2.3.5: Saving SystemState in data EEPROM).

2.

SystemState = 1

LD3 blinks. The HSE crystal clock is selected as the master clock source to

demonstrate the effectiveness of the clock failure mechanism performed by the CSS

when the clock fails. In this case, the failure is induced when pressing Button2 (see

Figure 2: Application state machine).

However, the application is not stopped as the CSS switches automatically the master

clock source from the HSE to the HSI clock. The completion of the switching operation

Table 2.

Interrupt routine versus flag

Interrupt routine

Event

Flag

PortB_IRQHandler()

Button1 pressed

ButtonPressed set

Clk_IRQHandler()

Failure detected on HSE

clock and HSE = master

clock

CSS_flag set