NEC remote control protocol receiver for MSP430

mspremote.c

/* mspremote - NEC remote control protocol receiver for MSP430 */
/* by Boris Gjenero <[email protected]> */

#include <stdbool.h>
#include <msp430.h>
#include <msp430g2252.h>

#define P1_LED1   0x01
#define P1_REMOTE 0x10

#define REMOTE_SHORT_MIN 400
#define REMOTE_SHORT_MAX 700
#define REMOTE_LONG_MIN 1500
#define REMOTE_LONG_MAX 1800

static unsigned char timer_overflow = 0;
static unsigned short last_transition = 0;
static unsigned char remote_bits;
static unsigned short remote_accumulator, remote_address, remote_command;

void static inline remote_abort(void)
{
    remote_bits = 0;
}

bool static inline remote_burst(unsigned short len)
{
    if (len > REMOTE_SHORT_MIN && len < REMOTE_SHORT_MAX) {
        if (remote_bits == 16) {
            remote_address = remote_accumulator;
        } else if (remote_bits == 32) {
            remote_command = remote_accumulator;
            remote_bits = 0;
            return true;
        }
    } else {
        remote_abort();
    }
    return false;
}

void static inline remote_space(unsigned short len)
{
    if (len > REMOTE_SHORT_MIN && len < REMOTE_SHORT_MAX) {
        remote_bits++;
        remote_accumulator >>= 1;
    } else if (len > REMOTE_LONG_MIN && len < REMOTE_LONG_MAX) {
        remote_bits++;
        remote_accumulator >>= 1;
        remote_accumulator |= 0x8000;
    } else {
        remote_abort();
    }
}

// Timer 0 vectored interrupt handler
#pragma vector = TIMER0_A1_VECTOR
__interrupt void Timer_A1_ISR(void)
{
    switch (__even_in_range(TA0IV, TA0IV_TAIFG)) { // Use calculated branching
        case TA0IV_TACCR2: {
            unsigned short taccr = TA0CCR2, len;
            unsigned char port = P1IN;

            len = taccr - last_transition;
            last_transition = taccr;

            /* After a single overflow, unsigned subtraction works fine. After
             * multiple overflows, length is unknown but certainly too long.
             * COV and CCIFG check avoids situations where the pin changed
             * again since the change which triggered the interrupt, and the
             * port value may be misleading.
             */
            if (timer_overflow < 2 && (TA0CCTL2 & (COV | CCIFG)) == 0) {
                /* A space is high and a burst is low, but both are measured
                 * after they end, and the pin is in the opposite state. */
                if (port & P1_REMOTE) {
                    if (remote_burst(len)) LPM0_EXIT;
                } else {
                    remote_space(len);
                }
            } else {
                TA0CCTL2 &= ~COV;
                remote_abort();
            }
            timer_overflow = 0;
            break;
        }
        case TA0IV_TAIFG:
            if (timer_overflow == 0) {
                timer_overflow = 1;
            } else {
                timer_overflow = 2;
            }
            break;
    }
}

int main(void) {
    WDTCTL = WDTPW | WDTHOLD;    // Stop watchdog timer

    DCOCTL = 0x00;               // Set DCOCLK to 1MHz
    BCSCTL1 = CALBC1_1MHZ;
    DCOCTL = CALDCO_1MHZ;

    P1DIR = P1_LED1;
    P1SEL = P1_REMOTE;
    P1SEL2 = P1_REMOTE;          // Required to route input to TA0

    TA0CTL = TASSEL_2 | MC_2 | TACLR | TAIE;
    TA0CCTL2 = CM_3 | SCS | CAP | CCIE;

    __enable_interrupt();
    while (1) {
        LPM0;
        P1OUT ^= P1_LED1;
    }

    //return 0;
}