/***
 *** Serial Port driver for 12f1840 and kin
 ***/

#include "user.h"
#include "system.h"

#include <stdint.h>
#include <stdbool.h>


/* outgoing text buffer */
char outbuff[100];
char * outp = 0;
uint8_t outlen = 0;

/* incoming text buffer */
char inbuff[10];
uint8_t inlen = 0;


void serial_init(void)
{
    /* Enabling transmitter 26.1.1.1 page 259 - TX/CK I/O pin */
    TXSTAbits.TXEN = 1;
    TXSTAbits.SYNC = 0;
    RCSTAbits.SPEN = 1;
    /* Enabling receiver 26.1.2 page 262 - RX/DT I/O pin */
    RCSTAbits.CREN = 1;

    /* Select pins 4&5 as the uart - page 102 */
    APFCONbits.RXDTSEL = 1; /* RX/DT on RA5 */
    APFCONbits.TXCKSEL = 1; /* TX/CK on RA4 */
    TRISAbits.TRISA5 = 1;   /* RA5 as input  */
    TRISAbits.TRISA4 = 0;   /* RA4 as output */

    ANSELAbits.ANSA4 = 0; /* no analog */

#if _XTAL_FREQ != 4000000L
#error "Adjust serial port baudrate settings"
#endif
    
    /* assume 4MHz clock, 19k2 baud */
    TXSTAbits.BRGH = 0;
    BAUDCONbits.BRG16 = 1;
    SPBRG = 12;

    /* Enable interrupts */
    INTCONbits.GIE = 1;
    INTCONbits.PEIE = 1;

    /* enable uart receiver interupt */
    PIE1bits.RCIE = 1;
}


/* is the queue empty yet */
bool msg_empty(void)
{
    if (outp == 0) return 1;
    return 0;
}

/* new message in the queue */
void msg_write(const char *msg)
{
    char * p = outbuff + outlen;
    while (outlen < sizeof(outbuff) && *msg != 0) {
        *(p++) = *(msg++);
        outlen++;
    }
    *p = 0;
    if (outp == 0) {
        outp = outbuff;
        PIE1bits.TXIE = 1;
    }
}

void msg_writebyte(const char msg)
{
    if (outlen+1 >= (uint8_t)sizeof(outbuff)) return;
    outbuff[outlen++] = msg;
    outbuff[outlen] = 0;
    if (outp == 0) {
        outp = outbuff;
        PIE1bits.TXIE = 1;
    }
}

void putch(char data)
{
    msg_writebyte(data);
}

/* called from interrupt routine to send next char */
void msg_sendnext(void)
{
    /* we have finished, turn off the iterrupt */
    if (outp == 0 || *outp == 0) {
        PIE1bits.TXIE = 0;
        outp = 0;
        outlen = 0;
        return;
    }
    TXREG = *outp;
    outp++;
}

/* called from interrupt routine to receive next byte */
void msg_recvnext(void)
{
    while (PIR1bits.RCIF) {
        bool err = RCSTAbits.FERR;
        char new = RCREG;

        /* bad char, skip it */
        if (err) continue;

        /* our input buffer has overflowed */
        if (inlen > sizeof(inbuff)) return;

        /* keep this one */
        inbuff[inlen++] = new;
    }
}

bool msg_recvready(void)
{
    if (inlen > 0) return 1;
    return 0;
}

char msg_recv(void)
{
    if (inlen == 0) return 0;

    /* record and disable the interupt */
    bool in = PIE1bits.RCIE;
    PIE1bits.RCIE = 0;

    char new = inbuff[0];
    inlen--;

    /* shuffle them down one */
    for (char i=0;i<inlen;i++)
        inbuff[i] = inbuff[i+1];

    /* restore the interupt */
    PIE1bits.RCIE = in;
    return new;
}