/* p5_9.c Input Capture of PB04 using TC4
 *
 * This program uses TC4 to do input capture of PB04.
 * Captured time is store in the variable timestamp.
 * Period of input signal is calculated and stored in variable period.
 * Both variables are put in global for ease of observation in debugger.
 *
 * Test signal generation:
 * TC6 is used to generate signal to test input capture
 * The output at PB02 is 1 Hz.
 *
 * Signal capture:
 * A jumper is installed between PB02 and PB04. PB04 acts as the input
 * for EXTINT4.
 *
 * Event generation:
 * EXTINT4 is used to generate events.
 *
 * Event channel:
 * Event generated by EXTINT4 is fed into channel 8 of EVSYS.
 * Event user TC4 takes events from channel 8.
 *
 * Event consumption:
 * TC4 is configured to do capture to CC0.
 * When event occurs, the captured clock counts are stored
 * in global variables "timestamp" to be observed in debugger.
 * The event frequency is 1 Hz, the TC4 prescaler divides by 256,
 * the period should be 1,000,000/256=3,906.
 * The LED0 is also toggled when capture occurs.
 *
 * Tested with Atmel Studio 7 v7.0.1006 and Keil MDK-ARM v5.21a.
 */

#include "samd21.h"

unsigned char* ARRAY_PORT_PINCFG1 = (unsigned char*)&REG_PORT_PINCFG1;
unsigned char* ARRAY_PORT_PMUX1 = (unsigned char*)&REG_PORT_PMUX1;
void TC6_init(void);

uint16_t timestamp;
uint16_t period;

int main (void) {
    uint16_t reading;

    /* TC4 is configured to do event capture channel 0.
     * Counter is 16-bit mode, prescaler div by 256.
     */
    REG_PM_APBCMASK |= 0x00001000;  /* enable bus clock for TC4 */
    REG_GCLK_CLKCTRL = 0x401C;      /* GCLK0 -> TC4/TC5 */
    REG_TC4_CTRLA = 1;              /* reset */
    while (REG_TC4_CTRLA & 1) {}    /* wait till out of reset */
    REG_TC4_CTRLA = 0x0600;         /* div by 256, 16-bit mode */
    REG_TC4_CTRLC = 0x10;           /* enable capture ch 0 */
    REG_TC4_EVCTRL = 0x0020;        /* event input enabled */
    REG_TC4_INTFLAG = 0xFF;         /* clear all flags */
    REG_TC4_CTRLA |= 2;             /* enable TC4 */

    /* Configure PB04 as input for EXTINT4.
     * EXTINT4 is used to generate event on rising edge of PB04.
     */
    ARRAY_PORT_PINCFG1[4] |= 7;     /* enable PMUX function, input, pull */
    ARRAY_PORT_PMUX1[2] = 0;        /* PB04 = EXTINT4 */
    REG_PORT_DIRCLR1 = 0x10;        /* PB04 input */
    REG_PORT_OUTSET1 = 0x10;        /* PB04 pull-up */

    REG_GCLK_CLKCTRL = 0x4005;      /* GCLK0 -> EIC */
    REG_EIC_CONFIG0 |= 0x00010000;  /* EXTINT4 rising edge */
    REG_EIC_EVCTRL |= 0x10;         /* enable EXTINT4 event */
    REG_EIC_CTRL = 2;               /* enable EIC */

    /* EXTINT4 event feeds to channel 8.
     * TC4 uses events from channel 8.
     */
    REG_PM_APBCMASK |= 2;           /* clock to EVSYS */
    REG_EVSYS_CTRL = 1;             /* reset event system */
    REG_EVSYS_CHANNEL = 0x02100008; /* channel 8 <- EXTINT4 asynch */
    REG_EVSYS_USER = 0x0913;        /* channel 8 used by TC4 */

    /* TC6 is used to generate test signal */
    TC6_init();
    /* make PB30 output for LED */
    REG_PORT_DIRSET1 = 0x40000000;

    while(1) {
        if (REG_TC4_INTFLAG & 0x10) {       /* if capture occurs */
            REG_TC4_INTFLAG = 0x10;         /* clear capture flags */
            reading = REG_TC4_COUNT16_CC0;  /* read the timestamp */
            period = reading - timestamp;   /* calculate the period */
            timestamp = reading;            /* the timestamp is stored */
            REG_PORT_OUTTGL1 = 1 << 30;     /* toggle LED */
        }
    }
}
/* TC6 is used to generate signal to test input capture.
 * In 16-bit match frequency mode, output toggles and
 * counter reset at CC0 match.
 * The output toggles at 1,000,000/256/1,953 = 2 Hz
 * and the output 1 Hz.
 * PB02 is used as output pin.
 */
void TC6_init(void) {
    REG_GCLK_CLKCTRL = 0x401D;      /* GCLK0 -> TC6/TC7 */
    REG_PM_APBCMASK |= 0x00004000;  /* enable TC6 Clock in PM */
    REG_TC6_CTRLA = 1;              /* reset */
    while (REG_TC6_CTRLA & 1) {}    /* wait till out of reset */
    REG_TC6_CTRLA = 0x0620;         /* div by 256, 16-bit mode, match frequency mode */
    REG_TC6_COUNT16_CC0 = 1953;     /* match value 0, top count, output toggle on match */
    REG_TC6_CTRLA |= 2;             /* enable */

    ARRAY_PORT_PINCFG1[2] |= 1;     /* make PB02 output for TC6/WO[0] */
    ARRAY_PORT_PMUX1[1] = 0x04;     /* PB02 = TC6 */
}