Can't use delay in a library class constructor?

Forum 2005-2010 (read only) Software Syntax & Programs
1

Can somebody please tell me why this isn't allowed?

I was trying to create a library for an SPI device, but when I instantiate a member of my library class at a global level, the whole program seems to go South, and not even the Setup() code gets executed. If I move my member declaration inside the Setup(), or Loop() functions then everything runs fine (except my variable scope is not as desired).
Looking into this I discovered that if I comment out the delay() function, which I'm using to time my chip reset then the program runs. Hmm.

Here is a very simple example that demonstrates this:
(note this program will "crash", i.e. setup code never executes, as shown, although no compile warnings or errors are given)

Library header: Mark.h

// library test - demonstrates problem with use of delay() in constructor
// written by Mark MacDonald, aka Madhusudana das

#ifndef Mark_h
#define Mark_h

//#include "WConstants.h"
#include "WProgram.h"


class Mark
{
  public:
    Mark();
    void test();
  private:

};

#endif

Library body: Mark.cpp

// Mark Library test
// created by Mark MacDonald, aka Madhusudana das

#include "Mark.h"


Mark::Mark()
{
// the delay() function seems to kill things right here if class instance is globally declared!
  delay(2);
}

/*******************************************************************************/

void Mark::test()
{
  Serial.print("test() works!");
  
}

And the Arduino demo sketch:

//test class constructor with delay

#include <Mark.h>

Mark me; // declaration located here causes crash due to delay() function in member constructor?

void setup()
{
//  Mark me; // uncomment this and comment the above declaration to see it not crash
  Serial.begin(9600);
  Serial.println("Are you ready?");
  me.test();
}

void loop()
{
}
2

I just thought I would add that the obvious work-around is to just create a class.begin() function that does the device initialization from a call inside setup().
Oh, yeah and not surprisingly the Spi functions I tried in the constructor killed the program during boot as well. Stuff like pinMode() works fine.

My original constructor contained the following

  pinMode(RESET_PIN,OUTPUT);
  digitalWrite(RESET_PIN,LOW);
  delay(2);
  digitalWrite(RESET_PIN,HIGH);
  delay(20);
  Spi.transfer(0x00);
  Spi.transfer(OPSTATUS<<2);

which I moved all to a begin() function and got around the killer constructor issue.
Back at the beginning then, can someone kindly show this idiot the fine print that says you aren't soposed to try to do this? :-?

3

Constructors of global instances are executed before the C language main() begins. Arduino's main() calls Arduino's init(), which sets up the interrupt routine that supports millis() and delay(). Thus, those routines won't work in constructors for global instances.

4

IC, said the blind man.