STMicroelectronics STM32 Cortex-M3, Manual

Page: 43 / 60

4.10 External Interrupts (IRQ)
1 Intro
2 Electrocardiogram ( Ecg ) Signals
The Electrocardiogram (
Ecg
)
•
Ecg
: electrical manifestation of heart activity recorded
from the body surface
•
monitoring of heart rate
The
Ecg
signal can be recorded fairly easily with surface
electrodes placed on the limbs and/or the chest, see pages 6 – 16
below.
Josef Goette 2 2009
4.10 External Interrupts (IRQ)
b
extInt
F Pin PA0 is configured to generate an external interrupt. Pressing this button will toggle
a LED.
One of the key improvements of the Cortex core over the earlier ARM CPUs is its interrupt struc-
ture and exception handling. The ARM7 and ARM9 cores had two interrupt lines: The fast in-
terrupt and the general purpose interrupt line. These two interrupt lines had to support all of
the interrupt sources within a given manufacturer’s microcontroller. How this was done varied
according to the implementation, so while the techniques used were broadly the same, the imple-
mentation differed between manufacturers.
Since the interrupt scheme is implemented in the Cortex-M3 core, the way of operating is for all
microcontroller s using this core equal.
4.10.1 Configuration
In the configuration wizard (see Figure 4.11 ) the external interrupts have to be enabled and con-
figured to a input pin.
!
Note that this input in the GPIO section as well has to be configured as an input!
Figure 4.11: External Interrupt Configuration Wizard
4.10.2 Functionality
An event (rising or/and falling edge, according to the configuration) on EXTI0 will call the func-
tion
void EXTI0 IRQHandler(void)
. In this function, the interrupt service routine (ISR) first
check which ISR is pending by reading the pending register EXTI PR. At the end of the ISR you
have to clear the pending ISR in the EXTI PR. See Listing
4.8 for an ISR example.
Listing 4.8:
ISR
void EXTI0 IRQHandler ( void )
{
i f ( EXTI
−
> PR & (1 << 0) )
{
// EXTI0 i n t e r r u p t pending ?
40
// your ISR code here
EXTI
−
> PR
|
= (1 << 0) ; // c l e a r pending i n t e r r u p t
}
}
Lukas Kohler 35