/*! Sends BYTE to the serial port. */
void serial_putc(uint8_t byte) {
enum intr_level old_level = intr_disable();
if (mode != QUEUE) {
/* If we're not set up for interrupt-driven I/O yet,
use dumb polling to transmit a byte. */
if (mode == UNINIT)
init_poll();
putc_poll(byte);
}
else {
/* Otherwise, queue a byte and update the interrupt enable register. */
if (old_level == INTR_OFF && intq_full(&txq)) {
/* Interrupts are off and the transmit queue is full.
If we wanted to wait for the queue to empty,
we'd have to reenable interrupts.
That's impolite, so we'll send a character via
polling instead. */
putc_poll(intq_getc (&txq));
}
intq_putc(&txq, byte);
write_ier();
}
intr_set_level(old_level);
}
/* Adds BYTE to the end of Q.
Q must not be full if called from an interrupt handler.
Otherwise, if Q is full, first sleeps until a byte is
removed. */
void
intq_putc (struct intq *q, uint8_t byte)
{
ASSERT (intr_get_level () == INTR_OFF);
while (intq_full (q))
{
ASSERT (!intr_context ());
lock_acquire (&q->lock);
wait (q, &q->not_full);
lock_release_with_preemption (&q->lock);
}
q->buf[q->head] = byte;
q->head = next (q->head);
signal (q, &q->not_empty);
}
/* 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))
|| (waiter == &q->not_full && !intq_full (q)));
