arduino software serial library that doesn't use interrupts

softare_uart.ino

// bits per second, measured in microseconds.
#define HALF_BIT_4800 104;
#define FULL_BIT_4800 208;


void setup() {
    // ...
}


void loop() {
    // ...
}


unsigned char uart_rx(int pin, int baud) {
    unsigned char rec = 0;
    // double pause = 0.0;
    // double half_pause = 0.0;
    int i = 0;

    // this is a bit pointless for now. we're only reading the GPS at 4800bps.
    // but might want to read it quicker in future...
    /* switch(baud) {
        case 4800:
        default:
            pause = FULL_BIT_4800;
            half_pause = HALF_BIT_4800;
            break;
    } */

    double pause = FULL_BIT_4800;
    double half_pause = HALF_BIT_4800;

    start_again:
        rec = 0;
        while(digitalRead(pin) == LOW);  // wait for line to be high
        while(digitalRead(pin) == HIGH);  // wait for line to fall (start bit)
        delayMicroseconds(half_pause);

        if(digitalRead(pin) != LOW) goto start_again;
        delayMicroseconds(pause);

        if(digitalRead(pin) == HIGH) rec += 1;
        delayMicroseconds(pause);

        if(digitalRead(pin) == HIGH) rec += 2;
        delayMicroseconds(pause);

        if(digitalRead(pin) == HIGH) rec += 4;
        delayMicroseconds(pause);

        if(digitalRead(pin) == HIGH) rec += 8;
        delayMicroseconds(pause);

        if(digitalRead(pin) == HIGH) rec += 16;
        delayMicroseconds(pause);

        if(digitalRead(pin) == HIGH) rec += 32;
        delayMicroseconds(pause);

        if(digitalRead(pin) == HIGH) rec += 64;
        delayMicroseconds(pause);

        if(digitalRead(pin) == HIGH) rec += 128;
        delayMicroseconds(pause);

        if(digitalRead(pin) != HIGH) goto start_again;

    return rec;
}


void uart_tx(char data, int baud, int pin) {
    /* double pause = 0;

    switch(baud) {
        case 4800:
        default:
            pause = FULL_BIT_4800;
            break;
    } */

    double pause = FULL_BIT_4800;

    digitalWrite(pin, LOW);  // transmit start bit
    delayMicroseconds(pause);

    if(data & 1) digitalWrite(pin, HIGH);
    else digitalWrite(pin, LOW);
    delayMicroseconds(pause);

    if(data & 2) digitalWrite(pin, HIGH);
    else digitalWrite(pin, LOW);
    delayMicroseconds(pause);

    if(data & 4) digitalWrite(pin, HIGH);
    else digitalWrite(pin, LOW);
    delayMicroseconds(pause);

    if(data & 8) digitalWrite(pin, HIGH);
    else digitalWrite(pin, LOW);
    delayMicroseconds(pause);

    if(data & 16) digitalWrite(pin, HIGH);
    else digitalWrite(pin, LOW);
    delayMicroseconds(pause);

    if(data & 32) digitalWrite(pin, HIGH);
    else digitalWrite(pin, LOW);
    delayMicroseconds(pause);

    if(data & 64) digitalWrite(pin, HIGH);
    else digitalWrite(pin, LOW);
    delayMicroseconds(pause);

    if(data & 128) digitalWrite(pin, HIGH);
    else digitalWrite(pin, LOW);
    delayMicroseconds(pause);

    digitalWrite(pin, HIGH); // transmit stop bit
    delayMicroseconds(pause);
}


void uart_str(char *str, int baud, int pin) {
    int i;
    for(i=0; i<strlen(str); i++) {
        uart_tx(str[i], baud, pin);
    }
}