ricardocosme / avrINT

C++11/17 facilities to use the interrupt capabilities of AVR

avrINT

C++11/17 facilities to use the interrupt capabilities of AVR. It can be thought as a C++ version to the C headers avr/interrupt.h and util/atomic.h from AVR Libc.(Why?)

Demo

#include <avr/interrupt.hpp>

using namespace avr::interrupt;

int main() {
    on(); //enable global interrupts
    off(); //disable global interrupts

    { //scope with code executed without being disturbed by interrupts
        atomic s;
        //code
    } //interrupts are enabled at the end if they were enabled before

    {
        atomic s{on_at_the_end};
        //code
    } //interrupts are always enabled at the end

    { //scope with code executed with interrupts enabled
        interruptible s;
        //code
    } //interrupts are disabled at the end if they were disabled before

    {
        interruptible s{off_at_the_end};
        //code
    } //interrupts are always disabled at the end
}

The demo above uses C++17 but C++11 can also be used, take a look at demo/atomic.cpp or demo/interruptible.cpp to see how.

API

Note, simplifications are taken into account in order to achieve a more expressive documentation, please, open avr/interrupt.hpp to see the real prototypes or declarations.

void on()

void sei()

Enable global interrupts.

void off()

void cli()

Disable global interrupts.

template<typename AtTheEnd> atomic::atomic(AtTheEnd = restore{})

RAII to execute code without being disturbed by interrupts. By default the state of the status register is recovered at the end of the scope, which means that global interrupts are enabled again only if they were enabled before. If the argument on_at_the_end is passed to the constructor then global interrupts are always enabled at the end of the scope.

Note, the compiler optimizer can reorder the code around the atomic scope that doesn’t have any observable side effect. Take a look at reordering_code.org if timing is a critical factor.

template<typename AtTheEnd> interruptible::interruptible(AtTheEnd = restore{})

RAII to execute code with interrupts enabled. By default the state of the status register is recovered at the end of the scope, which means that global interrupts are disabled again only if they were disabled before. If the argument off_at_the_end is passed to the constructor then global interrupts are always disabled at the end of the scope.

Note, the compiler optimizer can reorder the code around the atomic scope that doesn’t have any observable side effect. Take a look at reordering_code.org if timing is a critical factor.

template<typename T> void clobber(const T& v)

It communicates to the compiler that the lvalue v has an observable side effect. Take a look at reordering_code.org.

AVRINT_IST(vector, ...)

Macro to define ISR(Interrupt Service Routine) routines. The parameter vector is the name of the interrupt vector and the variable argument can be used to put additional attributes.

For each interrupt there is a short macro using the form AVRINT_<name_of_the_interrupt>(...). The <name_of_the_interrupt> is the one defined by the datasheet and sometimes there is a more extensive version with a more expressive name, for example, considering an ATtiny13A there is the macro AVRINT_TIM0_OVF(...) but there is also the alias AVRINT_TIMER_OVERFLOW(...).

How to use it?

1. Add the include directory to your include path and the include patch to avrIO(if you want to use it instead of avr/io.h).
2. Add #include <avr/interrupt.hpp> to your source and enjoy it!

Benchmark against AVR Libc

avrINT

void f() {
    avr::interrupt::on();
    avr::interrupt::off();
    avr::interrupt::atomic s;
    //code
}

/*
00000000 <_Z1fv>:
   0:	78 94       	sei
   2:	f8 94       	cli
   4:	8f b7       	in	r24, 0x3f	; 63
   6:	f8 94       	cli
   8:	8f bf       	out	0x3f, r24	; 63
   a:	08 95       	ret
*/

-std=c++17 -Os -mmcu=attiny13a

AVR Libc

void f() {
    sei();
    cli();
    ATOMIC_BLOCK(ATOMIC_RESTORESTATE) {
        //code
    }
}

/*
00000000 <_Z1fv>:
   0:	78 94       	sei
   2:	f8 94       	cli
   4:	8f b7       	in	r24, 0x3f	; 63
   6:	f8 94       	cli
   8:	8f bf       	out	0x3f, r24	; 63
   a:	08 95       	ret
*/
}

-std=c++17 -Os -mmcu=attiny13a

Requirements/Dependencies

1. avr-gcc with at least -std=c++11.
2. avrIO or avr/io.h from AVR Libc.

Contributions

Contributions are welcome, if you like what you see and you have interest to help, don’t hesitate to open a PR(pull request), a issue or contact me through my email.