/* p7_1.c: A to D conversion of channel 2 - LM34

 * This program converts the analog input from channel 2 (PB08)
 * which is connected to an LM34. External 3.3V is connected VREFA.
 * The conversion result is scaled to degree F and sent to
 * UART on SERCOM3 at 9600 Baud.
 * UART3 is connected to EDBG virtual connection to the host PC COM port.
 * Use TeraTerm to see the message "YES" on a PC.
 *
 * Tested with Atmel Studio 7 v7.0.1006 and Keil MDK-ARM v5.21a.
 */

#include "samd21.h"
#include <stdio.h>

unsigned char* ARRAY_PORT_PINCFG0 = (unsigned char*)&REG_PORT_PINCFG0;
unsigned char* ARRAY_PORT_PMUX0 = (unsigned char*)&REG_PORT_PMUX0;
unsigned char* ARRAY_PORT_PINCFG1 = (unsigned char*)&REG_PORT_PINCFG0;
unsigned char* ARRAY_PORT_PMUX1 = (unsigned char*)&REG_PORT_PMUX0;

void UART3_init(void);
void UART3_write(char data);
void UART3_puts(char* s);
void delayMs(int n);

int main (void) {
    int result;
    int temperature;
    char outbuf[20];
    
    UART3_init();

    REG_PM_APBCMASK |= 0x10000;         /* enable bus clock for ADC */
    REG_GCLK_CLKCTRL = 0x401E;          /* GCLK0 to ADC */
    REG_ADC_SAMPCTRL = 5;               /* sampling time 5 clocks */
    ARRAY_PORT_PINCFG0[3] |= 1;         /* Use PMUX for PA03 */
    ARRAY_PORT_PMUX0[1] = 0x10;         /* PA03 = VREFA */
    REG_ADC_REFCTRL = 3;                /* Use VREFA */
    REG_ADC_INPUTCTRL = 0x1802;         /* V- = GND; V+ = AIN2 */
    ARRAY_PORT_PINCFG1[8] |= 1;         /* Use PMUX for PB08 */
    ARRAY_PORT_PMUX1[4] = 0x10;         /* PB08 = AIN2 */
    REG_ADC_CTRLA = 2;                  /* enable ADC */

    while (1) {
        REG_ADC_SWTRIG = 2;             /* start a conversion */
        while(!(REG_ADC_INTFLAG & 1));  /* wait for conv complete */
        result = REG_ADC_RESULT;        /* read conversion result */

        temperature = result * 330 / 4096;
        sprintf(outbuf, "T = %d\r\n", temperature);
        UART3_puts(outbuf);
        delayMs(200);
    }
}

/* initialize UART3 to transmit at 9600 Baud */
void UART3_init(void) {
    REG_PM_APBCMASK |= 0x00000020;  /* enable bus clock for SERCOM3 */
    REG_GCLK_CLKCTRL = 0x4017;      /* GCLK0 to SERCOM3 */

    REG_SERCOM3_USART_CTRLA |= 1;               /* reset SERCOM3 */
    while (REG_SERCOM3_USART_SYNCBUSY & 1) {}   /* wait for reset to complete */
    REG_SERCOM3_USART_CTRLA = 0x40106004;       /* LSB first, async, no parity,
        PAD[0]-Tx, BAUD uses fraction, 8x oversampling, internal clock */
    REG_SERCOM3_USART_CTRLB = 0x00010000;       /* enable Tx, one stop bit, 8 bit */
    REG_SERCOM3_USART_BAUD  = 13;               /* 1000000/8/9600 = 13.02 */
    REG_SERCOM3_USART_CTRLA |= 2;               /* enable SERCOM3 */
    while (REG_SERCOM3_USART_SYNCBUSY & 2) {}   /* wait for enable to complete */
        
    ARRAY_PORT_PINCFG0[22] |= 1;    /* allow pmux to set PA22 pin configuration */
    ARRAY_PORT_PMUX0[11] = 0x02;    /* PA22 = TxD */
}


void UART3_write(char data) {
    while(!(REG_SERCOM3_USART_INTFLAG & 1)) {}  /* wait for data register empty */
    REG_SERCOM3_USART_DATA = data;              /* send a char */
}

void UART3_puts(char* s) {
    while (*s)
        UART3_write(*s++);
}

/* millisecond delay based on 1 MHz system clock */
void delayMs(int n) {
    int i;
    for (; n > 0; n--)
        for (i = 0; i < 199; i++)
            __asm("nop");
}