GRAINS Module

Hi slowscape,

I've done some digging and googleing and found one possible reason why Mozzi uses pin 9 instead of pin 11 and that may have to do with the timer interrupts that are responsible for that pin.

This website explains it in way too much detail for the uninitiated (that's me):

www.robotshop.com/community/forum/t/arduino-101-timers-and-interrupts/13072

But I can see that the gist of it is that pin 9 is accessed by timer1 which is a 16bit timer and pin 11 is accessed by timer2 which is only an 8bit timer. I assume that Tim Barrass chose pin 9 to achieve better sound quality due to a higher timer resolution.

Here is an excerpt from the webpage above that supports this claim:

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There is fixed relation between the timers and the PWM capable outputs. When you look in the data sheet or the pinout of the processor these PWM capable pins have names like OCRxA, OCRxB or OCRxC (where x means the timer number 0..5). The PWM functionality is often shared with other pin functionality.
The Arduino has 3Timers and 6 PWM output pins. The relation between timers and PWM outputs is:
Pins 5 and 6: controlled by timer0 (8bit)
Pins 9 and 10: controlled by timer1 (16bit)
Pins 11 and 3: controlled by timer2 (8bit)

Timer0:
Timer0 is a 8bit timer.
In the Arduino world timer0 is been used for the timer functions, like delay() 645, millis() 1.4k and micros() 651. If you change timer0 registers, this may influence the Arduino timer function. So you should know what you are doing.

Timer1:
Timer1 is a 16bit timer.
In the Arduino world the Servo library 1.0k uses timer1 on Arduino Uno (timer5 on Arduino Mega).

Timer2:
Timer2 is a 8bit timer like timer0.
In the Arduino work the tone() 847 function uses timer2.
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