PWM Motor control code for AIRBOAT running on ATTINY10

main.c

/*
 * Attiny10 AIRBOAT PWM Motor control code
 *
 * Created: 12/2/2016 6:17:47 PM
 * Author : josh
 */ 

#include <avr/io.h>
#include <util/delay.h>


// MOTOR FUNCTIONS
// ===============
// Note that register values are hard coded rather than #defined because they
// can not just be moved around. They depend on the Timer hardware of the specific chip/pin.

// Motor is controller by an N-MOSFET which is connected to pin OC0B (pin #3 on ATTINY10 SOT-23).  
// 1 output turns motor on, 0 is off.


// Initialize the motor pin. Sets to output mode, which will drive pin LOW.
// Call this as soon as possible after reset to keep the mosfet from floating and turning on the motor.

static void initMotor() {
    
    DDRB |= _BV(1);		// Set pin to output mode. It will already be low because IO ports default to 0 on reset.
    
}


// Turn the motor completely off- disconnects from PWM generator

static void motorOff(void) {

    TCCR0A &= ~( _BV(COM0B0) | _BV(COM0B1) );       // Set COM0B0 and COM0B1 to 0, "Normal port operation, OC0B disconnected"Z
    
    // Will revert the pin output back to PORT value, which we always keep at the default (zero).
    
}


// Set motor PWM

// match sets the duty cycle and should be between 0 and top. 0=completely off, top=full on.
// top sets the frequency where PWM frequency = F_CPU/top. The minimum resolution allowed is 2-bit (top set to 0x0003).

// Note: Currently disables OCR0A, but could easily be changed to preserve OCR0A through speed changes if wanted.
// Note: Clobbers ICR0 for TOP function.
// Note: Resets all used registers each time from scratch for safety from glitches. This is probably  unnecessary...
//       http://electronics.stackexchange.com/questions/139575/how-often-do-avrs-actually-glitch-and-need-a-watch-dog-reset-in-the-real-world/144318


static void setMotorPWM( uint16_t match , uint16_t top ) {
    
    if (match==0) {			// Special case this because the PWM generator still generates a pulse at 0 duty cycle
        // "If the OCR1x is set equal to BOTTOM (0x0000) the output will be a narrow spike for each TOP+1 timer clock cycle."
        
        motorOff();
        
    } else {
        
        TCCR0A = 
            _BV(COM0B1) |         // Clear OC0B on compare match (non-inverting)
            _BV(WGM01)            // Mode 14 1110, Fast PWM TOP=ICR0
            ;                     // Note that this clears the OC0A COM bits as side effect, but those could be preserved if wanted
    
        TCCR0B = 
            _BV( WGM03) | _BV( WGM02 ) |        // Mode 14 1110, Fast PWM TOP=ICR0
            _BV( CS00  )                        // prescaler=clk/1
        ;
        
                                                                    
        OCR0B = match;
        
        ICR0 = top;	// Counter top value - resets to zero when we get here
        
        if (TCNT0 > top ) {     // Handle the glitch in the case where changing TOP leads a missed match and a full wrap of TCNT
            
            TCNT0 = top-1;
            
        }
        
        // Note that there is a silicon bug that might make this not work on older parts:
        // http://electronics.stackexchange.com/questions/97596/attiny85-pwm-why-does-com1a0-need-to-be-set-before-pwm-b-will-work
        
    }
    
}




int main(void)
{
    
    DDRB |= _BV( 2 );       // Set pin PB2 to output so we can blink an attached LED for feedback
    
    initMotor();
    
    while (1) 
    {
        PINB |= _BV( 2 );   // Blink LED once per cycle so we know we are running!
        _delay_ms(500);
        
        setMotorPWM( 10 , 100 );
        _delay_ms(1000);
        
        setMotorPWM( 100 , 1000 );
        _delay_ms(1000);
       
        setMotorPWM( 1000 , 10000 );
        _delay_ms(1000);
        
        motorOff();
        _delay_ms(1000);
        

        setMotorPWM( 20 , 100 );
        _delay_ms(1000);
        
        setMotorPWM( 50 , 100 );
        _delay_ms(1000);
        
        setMotorPWM( 80 , 100 );
        _delay_ms(1000);
        
        motorOff();
        _delay_ms(1000);

        
    }
}