/* p7_3.c: LM34 Fahrenheit temperature sensor
 *
 * LM34 is a Fahrenheit temperature sensor with the output of
 * 10 mV/degreeF. The program assumes an LM34 connected to 
 * pin PC0 (channel 10). The conversion result is displayed one
 * the console as degree Fahrenheit.
 * The console UART driver is from Program 4-5.
 * This program was tested with Keil uVision v5.24a with DFP v2.11.0.
 */

#include "stm32f4xx.h"
#include <stdio.h>

void USART2_init(void);
int USART2_write(int c);
void delayMs(int n);

int main (void) {
    int result;
    double temp;

    /* set up pin PC0 for analog input */
    RCC->AHB1ENR |=  4;	            /* enable GPIOC clock */
    GPIOC->MODER |=  3;             /* PC0 analog */

    /* setup ADC1 */
    RCC->APB2ENR |= 0x00000100;     /* enable ADC1 clock */
    ADC1->CR2 = 0;                  /* SW trigger */
    ADC1->SQR3 = 10;                /* single conversion ch 10 */
    ADC1->SQR1 = 0;                 /* conversion sequence length 1 */
    ADC1->CR2 |= 1;                 /* enable ADC1 */
    
    /* initialize USART2 for output */
    USART2_init();
    printf("LM34 Temperature Sensor\r\n");

    while (1) {
        ADC1->CR2 |= 0x40000000;        /* start a conversion */
        while(!(ADC1->SR & 2)) {}       /* wait for conv complete */
        result = ADC1->DR;              /* read conversion result */
        temp = (double)result / 4095 * 330;
        printf("%d, %.2f\r\n", result, temp);
        delayMs(1000);
    }
}
/* initialize USART2 to transmit at 9600 Baud */
void USART2_init (void) {
    RCC->AHB1ENR |= 1;          /* Enable GPIOA clock */
    RCC->APB1ENR |= 0x20000;    /* Enable USART2 clock */

    /* Configure PA2 for USART2_TX */
    GPIOA->AFR[0] &= ~0x0F00;
    GPIOA->AFR[0] |=  0x0700;   /* alt7 for USART2 */
    GPIOA->MODER  &= ~0x0030;
    GPIOA->MODER  |=  0x0020;   /* enable alternate function for PA2 */
    USART2->BRR = 0x0683;       /* 9600 baud @ 16 MHz */
    USART2->CR1 = 0x000C;       /* enable Tx, Rx, 8-bit data */
    USART2->CR2 = 0x0000;       /* 1 stop bit */
    USART2->CR3 = 0x0000;       /* no flow control */
    USART2->CR1 |= 0x2000;      /* enable USART2 */
}
/* Write a character to USART2 */
int USART2_write (int ch) {
    while (!(USART2->SR & 0x0080)) {}   // wait until Tx buffer empty
    USART2->DR = ch;
    return ch;
}
/* The code below is the interface to the C standard I/O library.
 * All the I/O are directed to the console, which is UART2.
 */
struct __FILE { int handle; };
FILE __stdout = {1};

/* Called by C library console/file output */
int fputc(int c, FILE *f) {
    return USART2_write(c);  /* write the character to console */
}

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