led.c

// blinking LED
//
// set lfuse to 0x5E for 20 MHz xtal
// 115200 baud serial
//
// Anish Athalye
//
// some code from http://academy.cba.mit.edu/classes/embedded_programming/hello.ftdi.44.echo.c
// license for that:
//
// Neil Gershenfeld
// 12/8/10
//
// (c) Massachusetts Institute of Technology 2010
// This work may be reproduced, modified, distributed,
// performed, and displayed for any purpose. Copyright is
// retained and must be preserved. The work is provided
// as is; no warranty is provided, and users accept all 
// liability.

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

#define LEDPORT (PORTA)
#define LEDDDR (DDRA)
#define LED_R (PA2)
#define LED_G (PA3)
#define LED_B (PA7)
#define SETB(byte, bit) (byte |= (1 << bit))
#define CLRB(byte, bit) (byte &= (~ (1 << bit)))
#define ASSIGNB(test, byte, bit) do { if (test) SETB(byte, bit); else CLRB(byte, bit); } while (0);

int pwm_ctr = 0;
int pwm_r = 0;
int pwm_g = 0;
int pwm_b = 0;
#define PWM_VALUES (20) // must be <= 0b00111111
// pwm_{color} values can go from [0, PWM_VALUES]
// 0 is off, and PWM_VALUES is full brightness
#define PWM_HZ (50)
#define PWM_TICKS (PWM_VALUES * PWM_HZ)

#define output(directions,pin) (directions |= pin) // set port direction for output
#define set(port,pin) (port |= pin) // set port pin
#define clear(port,pin) (port &= (~pin)) // clear port pin
#define pin_test(pins,pin) (pins & pin) // test for port pin
#define bit_test(byte,bit) (byte & (1 << bit)) // test for bit set
#define bit_delay_time 8.5 // bit delay for 115200 with overhead
#define bit_delay() _delay_us(bit_delay_time) // RS232 bit delay
#define half_bit_delay() _delay_us(bit_delay_time/2) // RS232 half bit delay
#define char_delay() _delay_ms(10) // char delay

#define serial_port PORTA
#define serial_direction DDRA
#define serial_pins PINA
#define serial_pin_in (1 << PA0)
#define serial_pin_out (1 << PA1)

void get_char(volatile unsigned char *pins, unsigned char pin, unsigned char *rxbyte)
{
   //
   // read character into rxbyte on pins pin
   //    assumes line driver (inverts bits)
   //
   *rxbyte = 0;
   while (pin_test(*pins,pin))
      //
      // wait for start bit
      //
      ;
   cli(); // disable interrupts
   //
   // delay to middle of first data bit
   //
   half_bit_delay();
   bit_delay();
   //
   // unrolled loop to read data bits
   //
   if pin_test(*pins,pin)
      *rxbyte |= (1 << 0);
   else
      *rxbyte |= (0 << 0);
   bit_delay();
   if pin_test(*pins,pin)
      *rxbyte |= (1 << 1);
   else
      *rxbyte |= (0 << 1);
   bit_delay();
   if pin_test(*pins,pin)
      *rxbyte |= (1 << 2);
   else
      *rxbyte |= (0 << 2);
   bit_delay();
   if pin_test(*pins,pin)
      *rxbyte |= (1 << 3);
   else
      *rxbyte |= (0 << 3);
   bit_delay();
   if pin_test(*pins,pin)
      *rxbyte |= (1 << 4);
   else
      *rxbyte |= (0 << 4);
   bit_delay();
   if pin_test(*pins,pin)
      *rxbyte |= (1 << 5);
   else
      *rxbyte |= (0 << 5);
   bit_delay();
   if pin_test(*pins,pin)
      *rxbyte |= (1 << 6);
   else
      *rxbyte |= (0 << 6);
   bit_delay();
   if pin_test(*pins,pin)
      *rxbyte |= (1 << 7);
   else
      *rxbyte |= (0 << 7);
   //
   // wait for stop bit
   //
   bit_delay();
   half_bit_delay();
   sei(); // reenable interrupts
}

int main(void)
{
    // set clock divider to /1
    CLKPR = (1 << CLKPCE);
    CLKPR = (0 << CLKPS3) | (0 << CLKPS2) | (0 << CLKPS1) | (0 << CLKPS0);

    // configure timer1 for CTC (clear timer on compare) mode
    TCCR1B |= (1 << WGM12);
    // enable the CTC interrupt
    TIMSK1 |= (1 << OCIE1A);
    // enable global interrupts
    sei();
    // start the timer at 20MHz / 1024
    TCCR1B |= ((1 << CS10) | (1 << CS12));
    // set the CTC compare value
    // timer is incrementing at 20MHz / 1024 = 19531.25 Hz
    // if want 100Hz pwm for example, the timer max count should be set to
    // 19531.25 Hz / 100 Hz = 195
    OCR1A = 19531.25 / PWM_TICKS;


    // set to output port
    LEDDDR |= (1 << LED_R | 1 << LED_G | 1 << LED_B);

    // make everything off
    SETB(LEDPORT, LED_G);
    SETB(LEDPORT, LED_R);
    SETB(LEDPORT, LED_B);

    unsigned char input, color, value;
    while (1)
    {
        get_char(&serial_pins, serial_pin_in, &input);
        // protocol: c = CCVVVVVV
        // where CC is the color channel
        // and VV is the value
        // CC: 0 = R, 1 = G, 2 = B, 3 = nothing
        // VVVVVV: value from 0x00 to PWM_VALUES
        color = input >> 6;
        value = input & 0x3f;
        if (0 <= value && value <= PWM_VALUES)
        {
            if (color == 0)
                pwm_r = value;
            if (color == 1)
                pwm_g = value;
            if (color == 2)
                pwm_b = value;
        }
                
    };
}

ISR(TIM1_COMPA_vect)
{
    if (pwm_ctr >= pwm_r)
    {
        SETB(LEDPORT, LED_R); // off
    }
    else
    {
        CLRB(LEDPORT, LED_R); // on
    }

    if (pwm_ctr >= pwm_g)
    {
        SETB(LEDPORT, LED_G); // off
    }
    else
    {
        CLRB(LEDPORT, LED_G); // on
    }

    if (pwm_ctr >= pwm_b)
    {
        SETB(LEDPORT, LED_B); // off
    }
    else
    {
        CLRB(LEDPORT, LED_B); // on
    }

    pwm_ctr++;
    if (pwm_ctr >= PWM_VALUES)
    {
        pwm_ctr = 0;
    }
}