Computers as Components, 2nd Edition

3.1 Programming Input and Output 101

io_buf[buf_tail++] = achar;

/* check pointer */

if (buf_tail == BUF_SIZE)

buf_tail = 0;

}

char remove_char() { /* take a character from the buffer

head */

char achar;

achar = io_buf[buf_head++];

/* check pointer */

if (buf_head == BUF_SIZE)

buf_head = 0;

}

Assume that we have two interrupt handling routines defined in C, input_handler for the

input device and output_handler for the output device. These routines work with the device

in much the same way as did the busy-wait routines. The only complication is in starting

the output device: If io_buf has characters waiting, the output driver can start a new output

transaction ...