@item serial.c
@itemx serial.h
Serial port driver. Again, @func{printf} calls this code for you,
-so you don't need to do so yourself. Feel free to look through it if
-you're curious.
+so you don't need to do so yourself.
+It handles serial input by passing it to the input layer (see below).
@item disk.c
@itemx disk.h
Supports reading and writing sectors on up to 4 IDE disks. This won't
actually be used until project 2.
+@item kbd.c
+@itemx kbd.h
+Keyboard driver. Handles keystrokes passing them to the input layer
+(see below).
+
+@item input.c
+@itemx input.h
+Input layer. Queues input characters passed along by the keyboard or
+serial drivers.
+
@item intq.c
@itemx intq.h
Interrupt queue, for managing a circular queue that both kernel
than the currently running thread, the current thread should
immediately yield the processor to the new thread. Similarly, when
threads are waiting for a lock, semaphore, or condition variable, the
-highest priority waiting thread should be woken up first. A thread
+highest priority waiting thread should be awakened first. A thread
may raise or lower its own priority at any time, but lowering its
priority such that it no longer has the highest priority must cause it
to immediately yield the CPU.
You are probably looking at a backtrace that looks something like this:
@example
-0xc0108810: debug_panic (../../lib/kernel/debug.c:32)
-0xc010a99f: pass (../../tests/threads/tests.c:93)
-0xc010bdd3: test_mlfqs_load_1 (../../tests/threads/mlfqs-load-1.c:33)
-0xc010a8cf: run_test (../../tests/threads/tests.c:51)
-0xc0100452: run_task (../../threads/init.c:283)
-0xc0100536: run_actions (../../threads/init.c:333)
-0xc01000bb: main (../../threads/init.c:137)
+0xc0108810: debug_panic (lib/kernel/debug.c:32)
+0xc010a99f: pass (tests/threads/tests.c:93)
+0xc010bdd3: test_mlfqs_load_1 (...threads/mlfqs-load-1.c:33)
+0xc010a8cf: run_test (tests/threads/tests.c:51)
+0xc0100452: run_task (threads/init.c:283)
+0xc0100536: run_actions (threads/init.c:333)
+0xc01000bb: main (threads/init.c:137)
@end example
This is just confusing output from the @command{backtrace} program. It
to be @func{pass}.
@xref{Backtraces}, for more information.
+
+@item How do interrupts get re-enabled in the new thread following @func{schedule}?
+
+Every path into @func{schedule} disables interrupts. They eventually
+get re-enabled by the next thread to be scheduled. Consider the
+possibilities: the new thread is running in @func{switch_thread} (but
+see below), which is called by @func{schedule}, which is called by one
+of a few possible functions:
+
+@itemize @bullet
+@item
+@func{thread_exit}, but we'll never switch back into such a thread, so
+it's uninteresting.
+
+@item
+@func{thread_yield}, which immediately restores the interrupt level upon
+return from @func{schedule}.
+
+@item
+@func{thread_block}, which is called from multiple places:
+
+@itemize @minus
+@item
+@func{sema_down}, which restores the interrupt level before returning.
+
+@item
+@func{idle}, which enables interrupts with an explicit assembly STI
+instruction.
+
+@item
+@func{wait} in @file{devices/intq.c}, whose callers are responsible for
+re-enabling interrupts.
+@end itemize
+@end itemize
+
+There is a special case when a newly created thread runs for the first
+time. Such a thread calls @func{intr_enable} as the first action in
+@func{kernel_thread}, which is at the bottom of the call stack for every
+kernel thread but the first.
@end table
@menu
thus loses the CPU and is moved to the ready queue. Now @var{L}'s
old priority is restored while it is in the ready queue.
+@item Can a thread's priority change while it is blocked?
+
+Yes. While a thread that has acquired lock @var{L} is blocked for any
+reason, its priority can increase by priority donation if a
+higher-priority thread attempts to acquire @var{L}. This case is
+checked by the @code{priority-donate-sema} test.
+
@item Can a thread added to the ready list preempt the processor?
Yes. If a thread added to the ready list has higher priority than the
@item How does @func{thread_set_priority} affect a thread receiving donations?
-It should do something sensible, but no particular behavior is
-required. None of the test cases call @func{thread_set_priority} from a
-thread while it is receiving a priority donation.
+It sets the thread's base priority. The thread's effective priority
+becomes the higher of the newly set priority or the highest donated
+priority. When the donations are released, the thread's priority
+becomes the one set through the function call. This behavior is checked
+by the @code{priority-donate-lower} test.
@item Calling @func{printf} in @func{sema_up} or @func{sema_down} reboots!
projects / pintos-anon / blobdiff