jroeger23 / software_uart

An asynchronous software UART (yet TX only) library for avr chips (attiny registers)

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