Hi I’m really new to Kotlin Native. I’m trying to develop with Kotlin Nativ for Raspberry Pi. I succ...

# kotlin-native

[Roger Kreienbühl]

Hi
I’m really new to Kotlin Native.
I’m trying to develop with Kotlin Nativ for Raspberry Pi. I successfully added the pigpio library and can use it, but sometimes I have the problem, that the program exits with:
sigHandler: Unhandled signal 11, terminating

My code looks like this:

package ch.lichtwellenreiter.omrr

import kotlinx.cinterop.staticCFunction
import pigpio.*

const val GPIO_BUTTON = 6
var lastChange: UInt = 0u

fun main() {
    initGPIO()
    setupButton()

    while (true) {}
}

private fun initGPIO() {
    if (gpioInitialise() < 0) {
        println("GPIO Error initialising")
        return
    }
}

private fun setupButton() {
    val buttonPort = GPIO_BUTTON.toUInt()
    initPortWithMode(buttonPort, PI_INPUT)

    gpioSetAlertFunc(buttonPort, flankChangeDetected)
}

private fun initPortWithMode(port: UInt, mode: Int) {
    if (gpioSetMode(port, mode.toUInt()) < 0) {
        println("Could not set mode for GPIO$port")
        return
    }
}

val flankChangeDetected = staticCFunction<Int, Int, UInt, Unit> { gpio, level, tick ->
    val ticker = tick
    val pin = gpio
    val lvl = level


    when (lvl) {
        0 -> {
            val time = ticker - lastChange
            lastChange = ticker
            println(tick)
            if ((time > 55u && time < 61u) || (time > 113u && time < 119u)) println(time)
            println("Button Pressed down, level 0")
        }
        1 -> {
            val time = ticker - lastChange
            lastChange = ticker
            println(tick)
            if ((time > 55u && time < 61u) || (time > 113u && time < 119u)) println(time)
            println("Button released, level 1")
        }
        2 -> println("Button GPIO timeout, no level change")
    }
}

The error occurs not every time, I could not identify the exact place in code where it happens, but I think it is the access to lastChange inside the when expression.

Has anyone some experience with such errors?
Is there a way to copy the value from a C Int or UInt?

[Glen]

Hello @Roger Kreienbühl. I think

this KotlinConf talk▾

can help you.

[Roger Kreienbühl]

Hi @Glen
Thanks for your response. This talk was the starting point for actually get Kotlin Native a try. Sadly ther is no use of the callback function

val flankChangeDetected = staticCFunction<Int, Int, UInt, Unit> { gpio, level, tick ->

in the talk. Because signal 11 is a segment violation, I think the value of lastChange or tick causes the error.
Sometimes I compile the program and run it without errors, but sometimes the exactly same program (no changes) a second time compiled causes this error.

[Glen]

Weird behavior. Could it be a compiler bug?🤔

[Roger Kreienbühl]

I don’t know, this only happens if I want to access a value a second time as far as I can say

[Glen]

Please, @Roger Kreienbühl,why do you need lastChange as a global variable?

[Glen]

Why not make it local to the callback?

[Roger Kreienbühl]

Because I have to calculate the time since the last change of the pin level

[Roger Kreienbühl]

val time = ticker - lastChange

[Glen]

You could make lastChange local to the main() function.

[Roger Kreienbühl]

Hmm, but how to use it in

flankChangeDetected

[Glen]

You could make flankChangeDetected a higher-order function, with two parameters, the first being lastChange, and the second being the callback.

[Roger Kreienbühl]

Am I missing something? flankChangeDetected is called from C, how should this work?

[Glen]

You could write something like : val flankChangeDetected : ((change: Int, callback: staticCFunction<Int, Int, UInt, Unit>) -> Unit) = //callbackFunction .

[Glen]

And inside the callback function, you can call the change variable.

[Roger Kreienbühl]

Sorry, I amalso quiet new to Kotlin. At the moment I don’t see how I can set this as callback with

gpioSetAlertFunc(buttonPort, flankChangeDetected)

[Glen]

Please does it work when you compile and run?

[Roger Kreienbühl]

I have no clue how I should insert this in the code?
How can flankChangeDetected be registered as callback when I use it as higher-order function? The way you posted it, it looks like i can pass a callback function to flankChangeDetected , but flankChangeDetected is the callback function, which I need to use in gpioSetAlertFunc(buttonPort, flankChangeDetected) , or do I understand something wrong?

[Glen]

Yeah, its true. There is no way of doing that transformation.

[Roger Kreienbühl]

With some println I figured out, that the error definitely has to be on the line lastChange = ticker

[Glen]

OK.

[napperley]

Below is an example of doing a callback with Kotlin Native (based on the pigpio example - http://abyz.me.uk/rpi/pigpio/cif.html#gpioSetAlertFunc ):

fun aFunction(gpio: Int, level: Int, tick: UInt) {
    // May need to call this function if the callback is called from 
    // a different thread other than the main thread, otherwise a segmentation fault "might" occur.
    initRuntimeIfNeeded()
    println("GPIO $gpio became $level at $tick")
}

// Use staticCFunction function to convert a top level Kotlin function to a static C function.
gpioSetAlertFunc(4, staticCFunction(::aFunction))

[Roger Kreienbühl]

I have tried to change this whit no luck, the problem is the same
I also tried to print the global variable lastChange in the callback without any usage of tick, level or gpio and the error still occurs. It seems to me, that the access to the global variable lastChange inside the callback is the problem, access to tick, level or gpio works without any problems

[Glen]

Please, @Roger Kreienbühl, why do you need lastChange as a global variable? You could just create it inside the callback function.

[Roger Kreienbühl]

No, thats not possible, because the value that I set in one callback, I need in the next callback to compare them

[Glen]

Another suggestion(not sure whether it will work) is to create functions that access and modify the global variable. Something like fun setChange(newValue : UInt) { lastChange = newValue }

[Roger Kreienbühl]

I can try in the evening. Another idea that I had was, that the acces is not allowed if the callback is on another thread, so I will also try AtomicInt

[Glen]

Yeah, that seems like a good idea...

[Roger Kreienbühl]

Will give feedback when I have tried it

[Glen]

👍

[Roger Kreienbühl]

Sorry for my late feedback
I have found a solution now
With this code it works:

@SharedImmutable
val sharedData = SharedData()

class SharedData {
    var lastChange = AtomicInt(0)
}

[Glen]

Nice...