/*
 * This program controls the rotational speed and direction of
 * a DC motor.
 *
 * The EduBase board has a quad half-H-bridge motor driver
 * (TB6612FNG), which is capable of driving two DC motors
 * or a stepper motor with up to 15V and 1.2A continuous current.
 *
 * The enable pins of the half-bridge are connected to PB7-4.
 * These pins are shared with the LEDs.
 * The PWM inputs are connected to PB0 and PB1.
 *
 * The four output pins of the motor driver device are connected to
 * the blue terminals marked M1, M2, M3, and M4.  Use of external
 * power supply for motor is recommended.  External power should be
 * connected to the terminal T3 and the jumper J4 should be at EXT.
 *
 * This program uses PB5, 4 for direction control and PB0 for
 * PWM control.  The outputs are terminals M3 and M4.
 * The PWM is generated by TIM8_CH2.
 *
 * PWM1 - PB0 - TIM8_CH2 - AF3
 * LED1 - PB5
 * LED0 - PB4
 *
 * PWM2 - PB1 - TIM8_CH3 - AF3
 * LED2 - PB6
 * LED3 - PB7
 */

#include "stm32f4xx.h"

void delayMs(int n);

int main(void) {
    int pw = 0;

    RCC->AHB1ENR |=  2;             /* enable GPIOB clock */

    // set pins as output to control H-bridge
    GPIOB->MODER &= ~0x0000ff00;    /* clear pin mode */
    GPIOB->MODER |=  0x00005500;    /* set pins to output mode */

    // configure PB0 as TIM8_CH2 PWM output
    GPIOB->AFR[0] &= ~0x0000000F;
    GPIOB->AFR[0] |=  0x00000003;   /* PB0 pin for TIM8 */
    GPIOB->MODER  &= ~0x00000003;
    GPIOB->MODER  |=  0x00000002;   /* use alternate function */

    /* setup TIM8_CH2 */
    RCC->APB2ENR |= 2;              /* enable TIM8 clock */
    TIM8->PSC = 0;                  /* divided by 10 */
    TIM8->ARR = 4000 - 1;           /* divided by 3636 */
    TIM8->CNT = 0;                  /* clear counter */
    TIM8->CCMR1 = 0x6000;           /* PWM mode */
    TIM8->CCER = 0x0050;            /* enable PWM Ch2N and output */
    TIM8->CCR2 = 100 - 1;           /* pulse width 1/3 of the period */
    TIM8->BDTR |= 0x8000;           /* enable output */
    TIM8->CR1 = 1;                  /* enable timer */

    while(1) {
        /* decrease the pulse width gradually */
        for (pw = 3900; pw >100; pw -= 20) {
            TIM8->CCR2 = pw;
            delayMs(50);
        }

        /* increase the pulse width gradually */
        for (pw = 100; pw < 3900; pw += 20) {
            TIM8->CCR2 = pw;
            delayMs(50);
        }

        /* reverse the direction */
        GPIOB->BSRR = 0x00100000;
        GPIOB->BSRR = 0x00000020;

        /* decrease the pulse width gradually */
        for (pw = 3900; pw >100; pw -= 20) {
            TIM8->CCR2 = pw;
            delayMs(50);
        }

        /* increase the pulse width gradually */
        for (pw = 100; pw < 3900; pw += 20) {
            TIM8->CCR2 = pw;
            delayMs(50);
        }

        /* reverse the direction */
        GPIOB->BSRR = 0x00000010;
        GPIOB->BSRR = 0x00200000;
    }
}


/* 16 MHz SYSCLK */
void delayMs(int n) {
    int i;
    for (; n > 0; n--)
        for (i = 0; i < 3195; i++) ;
}