/* p7_1.c: A to D conversion of channel 1

 * This program converts the analog input from channel 1.
 * Channel 1 is connected to input from PA1.
 * Clock prescaler is left at 0 (divided by 2) and Sampling 
 * time is also left at default of 3 cycles.
 * Software trigger is used. The bit 8 of the conversion
 * result is used to turn on/off the LED0. For the full
 * scale of the reference voltage, the LED0 should be on
 * for 8 times.
 *
 * This program was tested with Keil uVision v5.24a with DFP v2.11.0.
 */

#include "stm32f4xx.h"

int main (void) {
    int result;

    /* set up pin PA5 for LED */
    RCC->AHB1ENR |=  1;	            /* enable GPIOA clock */
    GPIOA->MODER &= ~0x00000C00;    /* clear pin mode */
    GPIOA->MODER |=  0x00000400;    /* set pin to output mode */

    /* set up pin PA1 for analog input */
    RCC->AHB1ENR |=  1;	            /* enable GPIOA clock */
    GPIOA->MODER |=  0xC;           /* PA1 analog */

    /* setup ADC1 */
    RCC->APB2ENR |= 0x00000100;     /* enable ADC1 clock */
    ADC1->CR2 = 0;                  /* SW trigger */
    ADC1->SQR3 = 1;                 /* conversion sequence starts at ch 1 */
    ADC1->SQR1 = 0;                 /* conversion sequence length 1 */
    ADC1->CR2 |= 1;                 /* enable ADC1 */

    while (1) {
        ADC1->CR2 |= 0x40000000;        /* start a conversion */
        while(!(ADC1->SR & 2)) {}       /* wait for conv complete */
        result = ADC1->DR;              /* read conversion result */
        if (result & 0x100)
            GPIOA->BSRR = 0x00000020;   /* turn on LED */
        else
            GPIOA->BSRR = 0x00200000;   /* turn off LED */
    }
}