File content as of revision 4:962bf18523f4:

#include "ESP8266.h"

static Serial uart(p28, p27);
static ring_buffer rx_buffer = { { 0 }, 0, 0};

static void write_char(unsigned char c)
{
    int i = (unsigned int)(rx_buffer.head + 1) % SERIAL_BUFFER_SIZE;

    // if we should be storing the received character into the location
    // just before the tail (meaning that the head would advance to the
    // current location of the tail), we're about to overflow the buffer
    // and so we don't write the character or advance the head.
    if (i != rx_buffer.tail) {
        rx_buffer.buffer[rx_buffer.head] = c;
        rx_buffer.head = i;
    }
}

static void uart_irq_callback()
{
    // Note: you need to actually read from the serial to clear the RX interrupt
    while(uart.readable()) {
        write_char(uart.getc());
    }
}

int read_char(void)
{
    // if the head isn't ahead of the tail, we don't have any characters
    if (rx_buffer.head == rx_buffer.tail) {
        return -1;
    } else {
        unsigned char c = rx_buffer.buffer[rx_buffer.tail];
        rx_buffer.tail = (unsigned int)(rx_buffer.tail + 1) % SERIAL_BUFFER_SIZE;
        return c;
    }
}

int available(void)
{
    return (unsigned int)(SERIAL_BUFFER_SIZE + rx_buffer.head - rx_buffer.tail) % SERIAL_BUFFER_SIZE;
}

/**
 * 使用uart.printf或者uart.puts方法时, 当发送数据大于14个字符时, 就会出现异常(串口不断的输出不可显示的字符)
 * 因此, 相关字符串的打印使用下面的函数来完成, 虽然很简陋, 但是很管用!
 */
void uart_send_string(const char *str)
{
    if (!str)
        return;

    while(*str)
        uart.putc(*str++);
}

void ESP8266_init(void)
{
    uart.attach(&uart_irq_callback);
}