Solved this finally. The Atom Lite does not seem to have a pullup or pulldown resistor. By applying a resistor the problem seems to be solved and it is possible to detect Rising, Falling and Change states.

The following code does not work. The LED flickers, no matter what the signal on the used pin is. Tested on two Atoms. Also tested different mode (RISING, FALLING, CHANGE). The code is from Arduino site:

#include <M5Atom.h>

const byte ledPin = 22;
const byte interruptPin = 19;
volatile byte state = LOW;

void IRAM_ATTR blink()
{
state = ~state;
}

void setup()
{
pinMode(ledPin, OUTPUT);
pinMode(interruptPin, INPUT_PULLUP);
attachInterrupt(digitalPinToInterrupt(interruptPin), blink, FALLING);
}

void loop()
{
digitalWrite(ledPin, state);
}

Anyone an idea to solve this?

@m5stack said in 2 M5StickC devices, one can upload, other can not:

DuPont cable

I tried. After lowering the baud rate to 115.200 it did work once. Could not debug any more and 6 others tries did not succeed after that. So uploading final software on production stick could perhaps be successful after numerous tries, but that's all. Not a consistent environment to develop prototypes or products.

I have 2 M5StickC devices which I used both for several projects. Now, for some reason, I can not upload to one device, but I can to the other. I use the same settings, the same environment (either Visual Micro in Visual Studio for Arduino, or the Arduino SDK itself all running in Windows 10) and the same USB cable. Both devices seem to connect well. The only difference lies in the fact that one device shows itself on com4 while the other shows itself on com7. The last one has no problem, the first always comes with the error message: Timed out waiting for packet header. I did try lowering the upload speed. Nothing works.
What can be the solution? Is there a way to change the used port, make it com7 instead of 4? Any other suggestion is welcome.

@zontex Thanks. Hopefully this will be soon. Especially useful for controlling devices via smartphones.

As the title says. Is Wifi Direct available, now or in the future?

On Arduino using the M5Stack (in my case the Gray version) pin 21 is the pin to pass on to FastLed. For M5StickC it is pin 32.
That the M5Stack shows a bright white light for the first LED seems to occur when one also uses the M5.Power.begin() command.
This piece of code should work on both devices adjusted for the device in use:

//#include <M5StickC.h>
#include <M5Stack.h>
#include "FastLED.h"

CRGB leds[15];

void setup() 
{
M5.begin();
    FastLED.addLeds<NEOPIXEL, 21>(leds, 15); // M5Stack Gray
    //FastLED.addLeds<NEOPIXEL, 32>(leds, 15); // M5StickC 
}

void loop()
{
    static uint8_t hue = 0;
    if (255 == hue)
        hue = 0;
    else
        FastLED.showColor(CHSV(hue++, 255, 50));
    delay(50);
}

Some simple questions:

Controlling the LEDs works well, but how can I control the first LED? Most of the time it is a very bright white, but it can change.
How can I use the strip on a M5Stick C?

@Pepsi Thanks, I could not find the call to decrease the speed. Not very much, but it helps.