circular_buffer.c

#include <stdint.h>
#include <stdio.h>

#define BUFFER_SIZE 16

struct Buffer {
        uint8_t data[BUFFER_SIZE];
        uint8_t newest_index;
        uint8_t oldest_index;
};

/* static struct Buffer buffer; */

enum BufferStatus {BUFFER_OK, BUFFER_EMPTY, BUFFER_FULL};

enum BufferStatus bufferWrite(volatile struct Buffer *buffer, uint8_t byte) {
        uint8_t next_index = ((buffer->newest_index)+1) % BUFFER_SIZE;

        if (next_index == buffer->oldest_index) {
                return BUFFER_FULL;
        }
        buffer->data[buffer->newest_index] = byte;
        buffer->newest_index = next_index;
        return BUFFER_OK;
}

enum BufferStatus bufferRead(volatile struct Buffer *buffer, uint8_t *byte) {
        if (buffer->newest_index == buffer->oldest_index) {
                return BUFFER_EMPTY;
        }
        *byte = buffer->data[buffer->oldest_index];
        buffer->oldest_index = ((buffer->oldest_index)+1) % BUFFER_SIZE;
        return BUFFER_OK;
}

volatile struct Buffer rx_buffer = {{}, 0, 0};

ISR(USART_RX_vect) {
        bufferWrite(&rx_buffer, UDR0);
}

int main(int argc, char **argv) {
        uint8_t received_byte;
        enum BufferStatus status;

        while(1) {
                status = bufferRead(&rx_buffer, &received_byte);
                if (status == BUFFER_OK) {
                        printf("%c", received_byte);
                }
        }
        return 0;
}