Lighthouses 2

Just like the Knightrider 2 this is another port of one of my experiments to the Arduino Due. This time I port the lighthouses experiment. The challenge with this experiment is not the pin mappings but the timer. For the original lighthouses experiment I used the MsTimer2 library. See the crucial piece of code below.

#include <MsTimer2.h>

// ...

void setup() {
    MsTimer2::set(1, blink);
    MsTimer2::start();
}

Unfortunately this does not compile for the Due. Searching the internet I found out that ARM Cortex processors provide a “systicks” timer which typically runs at 100 Hz. As it turns out Atmel decided to implement it differently such that it runs at 1 kHz. Lucky me. This is exactly what I need. So the next question was how to register for the systicks.

A short call of “grep sysTick -i -r .” revealed the relevant source lines.

./hardware/arduino/sam/cores/arduino/cortex_handlers.c:extern int sysTickHook(void);
./hardware/arduino/sam/cores/arduino/cortex_handlers.c: if (sysTickHook())
./hardware/arduino/sam/cores/arduino/hooks.c:int sysTickHook(void) __attribute__ ((weak, alias("__false")));

Looking into the files it becomes clear that sysTickHook is implemented by Arduino as a weak symbol. That is: if I define this symbol it will overwrite the default. However my first attempt below did not work.

// sysTicks will be triggered once per 1 ms
int sysTickHook(void) {
    blink();
    return 0;
}

Some more searching turned out that CMSIS low level system API is compiled in C instead of C++. So the compiler must be explicitly told that this is a C symbol.

extern "C" {
    // sysTicks will be triggered once per 1 ms
    int sysTickHook(void) {
        blink();
        return 0;
    }
}

And hurray it works. The full solution now looks as exhibited below.

//
//  www.blinkenlight.net
//
//  Copyright 2015 Udo Klein
//
//  This program is free software: you can redistribute it and/or modify
//  it under the terms of the GNU General Public License as published by
//  the Free Software Foundation, either version 3 of the License, or
//  (at your option) any later version.
//
//  This program is distributed in the hope that it will be useful,
//  but WITHOUT ANY WARRANTY; without even the implied warranty of
//  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
//  GNU General Public License for more details.
//
//  You should have received a copy of the GNU General Public License
//  along with this program. If not, see http://www.gnu.org/licenses/


uint8_t ledpin(const int8_t led) {
    return led<14? led: led+(54-14);
}

uint8_t setOutput(uint8_t led) {
    pinMode(ledpin(led), OUTPUT);
    return 0;
}

template <uint8_t led, uint32_t d1, uint32_t d2, uint32_t d3, uint32_t d4,
                       uint32_t d5, uint32_t d6, uint32_t d7, uint32_t d8>
void light_my_fire() {
    static uint32_t phase = setOutput(led);

    phase = phase < d1+d2+d3+d4+d5+d6+d7+d8-1? phase+1: 0;

    digitalWrite(ledpin(led), phase < d1                  ? HIGH:
                              phase < d1+d2               ? LOW:
                              phase < d1+d2+d3            ? HIGH:
                              phase < d1+d2+d3+d4         ? LOW:
                              phase < d1+d2+d3+d4+d5      ? HIGH:
                              phase < d1+d2+d3+d4+d5+d6   ? LOW:
                              phase < d1+d2+d3+d4+d5+d6+d7? HIGH:
                                                            LOW);
}

extern "C" {
    // sysTicks will be triggered once per 1 ms
    int sysTickHook(void) {
        blink();
        return 0;
    }
}

void blink() {
    light_my_fire<0,  200, 2800,  200, 2800,  200, 5800,    0,    0>();  // Norderney
    light_my_fire<1, 3000, 3000, 3000, 3000,    0, 8500,    0,    0>();  // Pilsum
    light_my_fire<2,  700, 2300,  700, 2300,  700, 2300,  700, 5300>();  // Campen
    light_my_fire<3, 6000, 6000,    0,    0,    0,    0,    0,    0>();  // Schillig
    light_my_fire<4, 6000, 3000,    0,    0,    0,    0,    0,    0>();  // Voslap
    light_my_fire<5, 6000, 1000,    0,    0,    0,    0,    0,    0>();  // Tossens
    light_my_fire<6, 1000, 1000,    0,    0,    0,    0,    0,    0>();  // test1
    light_my_fire<7,  500,  500,    0,    0,    0,    0,    0,    0>();  // test2
}


void setup() {}
void loop() {}