/* p5_9.c Using TPM2 Channel 0 to measure input period.

 * This program uses TPM2 CH1 Input Edge-time Capture to measure 
 * the period of a periodic waveform.
 * MCGFLLCLK (41.94 MHz) is used as timer counter clock.
 * Prescaler is set to divided by 128. So the timer counter is
 * counting at 41.94 MHz / 128 = 327,656 Hz.
 * Timer 2 Channel 0 is configured as Input Edge-time Capture mode.
 * and the input is using PTA1.
 * When a rising edge occurs at PTA1, the timer counter value is
 * copied to TPM2_C0V and the CHF is set.
 * The program waits for CHF flag to set then calculates the
 * difference of the current value to the previous recorded value.
 * Bit 11-9 are used to control the tri-color LEDs.
 * The LED should change color when the input frequency is changing
 * below 642 Hz. Above 642 Hz, the number of clock cycles between
 * rising edges is too small to reach bit 9.
 */

#include <MKL25Z4.H>

int main (void) {
    unsigned short then = 0;
    unsigned short now = 0;
    unsigned short diff;
    
    /* Initialize GPIO pins for tri-color LEDs */
    SIM->SCGC5 |= 0x400;        /* enable clock to Port B */
    SIM->SCGC5 |= 0x1000;       /* enable clock to Port D */
    PORTB->PCR[18] = 0x100;     /* make PTB18 pin as GPIO */
    PTB->PDDR |= 0x40000;       /* make PTB18 as output pin */
    PORTB->PCR[19] = 0x100;     /* make PTB19 pin as GPIO */
    PTB->PDDR |= 0x80000;       /* make PTB19 as output pin */
    PORTD->PCR[1] = 0x100;      /* make PTD1 pin as GPIO */
    PTD->PDDR |= 0x02;          /* make PTD1 as output pin */
    /* end GPIO pin initialization for LEDs */
    
    /* Start of Timer code */
    SIM->SCGC5 |= 0x0200;       /* enable clock to Port A */
    PORTA->PCR[1] = 0x0300;     /* set PTA1 pin for TPM2CH0 */
    
    SIM->SCGC6 |= 0x04000000;   /* enable clock to TPM2 */
    SIM->SOPT2 |= 0x01000000;   /* use MCGFLLCLK as timer counter clock */
    
    TPM2->SC = 0;               /* disable timer while configuring */
    TPM2->SC = 0x07;            /* prescaler /128 */
    TPM2->MOD = 0xFFFF;         /* max modulo value */
    TPM2->CONTROLS[0].CnSC = 0x04;  /* IC rising edge */
    TPM2->SC |= 0x08;           /* enable timer */
    
    while (1) {
        while(!(TPM2->CONTROLS[0].CnSC & 0x80)) { } /* wait until the CHF is set */
        TPM2->CONTROLS[0].CnSC |= 0x80;             /* clear CHF */
        now = TPM2->CONTROLS[0].CnV;
        diff = now - then; /* you may put a breakpoint here and examine the values */
        then = now;         /* save the current counter value for next calculation */
        
        /* change LEDs according to bit 11-9 of the value of diff */
        diff = diff >> 9;
        if (diff & 1)    /* use bit 0 of diff to control red LED */
            PTB->PCOR = 0x40000;    /* turn on red LED */
        else
            PTB->PSOR = 0x40000;    /* turn off red LED */
        
        if (diff & 2)    /* use bit 1 of diff to control green LED */
            PTB->PCOR = 0x80000;    /* turn on green LED */
        else
            PTB->PSOR = 0x80000;    /* turn off green LED */
        
        if (diff & 4)    /* use bit 2 of diff to control blue LED */
            PTD->PCOR = 0x02;       /* turn on blue LED */
        else
            PTD->PSOR = 0x02;       /* turn off blue LED */
        /* end of LED code */
    }
}