Please explain this code to me

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

I found this piece of code that is used to provide power to a Wiichuck (converterboard for use with Wii Nunchuck)

static void nunchuck_setpowerpins()
{
#define pwrpin PC3
#define gndpin PC2
    DDRC |= _BV(pwrpin) | _BV(gndpin);
    PORTC &=~ _BV(gndpin);
    PORTC |=  _BV(pwrpin);
    delay(100);  // wait for things to stabilize        
}

Can someone explain what it exactly does?

2

It's doing the equivalent of

#define PWRPIN 17 // 3 + 14 == Analog Pin 3
#define GNDPIN 16 // 2 + 14 == Analog Pin 2
pinMode(PWRPIN, OUTPUT);
pinMode(GNDPIN, OUTPUT);
digitalWrite(PWRPIN, HIGH);
digitalWrite(GNDPIN, LOW);
delay(100);

But it's using direct port manipulation to do it.

3

That is easier to read and understand for me.

What is the advantage to use Arduino code or port manipulation?

4

While the port manipulation routines happen about 20x~40x faster than the digitalWrite() routines, it's ridiculous to use such low-level nonsense before a 100ms delay. As you just demonstrated, it doesn't make the code more readable or maintainable.

5

ok :wink:

thank you very much for explaining

6

What is the advantage to use Arduino code or port manipulation?

I suspect that the original author was not aware that the "analog pins" of the arduino could be manipulated with pinMode() and digitalWrite() (using the n+14 as pin number), and so dropped into the direct mode access that they knew would work...