Software UART (not invented here)

This is an asynchronus software UART library designed for ATTiny MCUs.
Currently it's TX only.

Functions

Transmit a single character (blocking until queued)

void uart_putc(const char c);

Try to transmit a single character, if UART is Busy, return UART_BUSY

uart_error_t uart_try_putc(const char c);

Transmit a series of characters (blocking until queued)

void uart_puts(const char *s, size_t len);

Try to transmit a string, if UART is Busy, return UART_BUSY

uart_error_t uart_try_puts(const char *s, size_t len);

Initialize UART

void uart_init();

Example

#include "software_uart/uart.h"

int main()
{
        uart_error_t ret;

        uart_init();

        /* Queue a message (this will block until the message was queued) */
        uart_puts("Hello, Universe!", 16);

retry:
        /* Queue a message if possible */
        ret = uart_try_puts("Hello, Universe?", 16);
        if(ret == UART_BUSY) {
                /* Do other stuff. */
                goto retry;
        }

        return 0;
}

NOTE: Interrupts shall not be disabled for long to ensure a stable transmission

Header configuration

All these definitions can be overwritten by defining them in the first place

The PORT register for UART

#define UART_PORT PORTB

The DDR register for UART

#define UART_DDR DDRB

The bit position for the UART tx pin

#define UART_TX_BIT PB1

The UART baudrate (a sane value for 1MHz would be 4800 baud)

#define UART_BAUDRATE 9600

Uncomment if parity bit shall be sent. 1 = odd parity 0 = even parity

// #define UART_PARITY 0

Buffer size for outgoing bytes (number of queue slots)

#define UART_BUFFER_SIZE 64