Max7219, quad encoder, better modularity w.r.t. clock ISRs

[larsimmisch]

Hi Ben,

this adds:

• support for the Max7219 (good for 8x8 LED matrices)
• support for Quadrature encoders
• better modularity for clock ISRs

The clock ISR modularity thingy works like this: if you #define CLOCK_NO_ISR before including the clock header, you write the ISR yourself, but get to reuse the clock16 ISR.

With the quad encoder, I've used it like this:

#define CLOCK_NO_ISR
#include <clock16.h>
#include <quadrature.h>

typedef _Quadrature<Pin::D5, Pin::D6, 0, 127> Quadrature;

ISR(TIMER0_OVF_vect)
{
    Quadrature::update();
    clock16_isr();
}

Oh yeah, we need a quad encoder example in arduino--.

[benlaurie]

Wow, I suck. I should check this is safe to merge - I notice you removed the NullPin class, not sure if that breaks stuff?

Also, why the change on the ports header?

[larsimmisch]

Ghosts from the past.

The NullPin class still exists - it's currently in spi.h. I think that was because that was the only place that used it. It could go back into arduino--.h

The ports header was changed to support more than just the ATMega328 - it was moved to defs/ports_mx8.h. There is now also defs/ports_tnx5.h.

I meant to setup a simulator based test chain to verify that the ATTiny platforms behaved as expected, but didn't get around to it.