/*! Update interrupt enable register. */
static void write_ier(void) {
uint8_t ier = 0;
ASSERT(intr_get_level() == INTR_OFF);
/* Enable transmit interrupt if we have any characters to transmit. */
if (!intq_empty(&txq))
ier |= IER_XMIT;
/* Enable receive interrupt if we have room to store any
characters we receive. */
if (!input_full())
ier |= IER_RECV;
outb(IER_REG, ier);
}
/* Removes a byte from Q and returns it.
Q must not be empty if called from an interrupt handler.
Otherwise, if Q is empty, first sleeps until a byte is
added. */
uint8_t
intq_getc (struct intq *q)
{
uint8_t byte;
ASSERT (intr_get_level () == INTR_OFF);
while (intq_empty (q))
{
ASSERT (!intr_context ());
lock_acquire (&q->lock);
wait (q, &q->not_empty);
lock_release_with_preemption (&q->lock);
}
byte = q->buf[q->tail];
q->tail = next (q->tail);
signal (q, &q->not_full);
return byte;
}
/* Returns the position after POS within an intq. */
static int
next (int pos)
{
return (pos + 1) % INTQ_BUFSIZE;
}
/* WAITER must be the address of Q's not_empty or not_full
member. Waits until the given condition is true. */
static void
wait (struct intq *q UNUSED, struct thread **waiter)
{
ASSERT (!intr_context ());
ASSERT (intr_get_level () == INTR_OFF);
ASSERT ((waiter == &q->not_empty && intq_empty (q))
|| (waiter == &q->not_full && intq_full (q)));
*waiter = thread_current ();
thread_block ();
}
/* WAITER must be the address of Q's not_empty or not_full
member, and the associated condition must be true. If a
thread is waiting for the condition, wakes it up and resets
the waiting thread. */
static void
signal (struct intq *q UNUSED, struct thread **waiter)
{
ASSERT (intr_get_level () == INTR_OFF);
ASSERT ((waiter == &q->not_empty && !intq_empty (q))
/*! Flushes anything in the serial buffer out the port in polling mode. */
void serial_flush(void) {
enum intr_level old_level = intr_disable();
while (!intq_empty(&txq))
putc_poll(intq_getc(&txq));
intr_set_level(old_level);
}
