Kernel: Add a beep() syscall that beeps the PC speaker.

Hook this up in Terminal so that the '\a' character generates a beep.
Finally emit an '\a' character in the shell line editing code when
backspacing at the start of the line.

Applications/Terminal/Terminal.cpp

@@ -576,7 +576,7 @@ void Terminal::on_char(byte ch)
         }
         return;
     case '\a':
-        // FIXME: Bell!
+        beep();
         return;
     case '\t': {
         for (unsigned i = m_cursor_column; i < columns(); ++i) {

Kernel/Devices/PCSpeaker.cpp

@@ -0,0 +1,20 @@
+#include <Kernel/Devices/PCSpeaker.h>
+#include <Kernel/i8253.h>
+#include <Kernel/IO.h>
+#include <Kernel/i386.h>
+
+void PCSpeaker::tone_on(int frequency)
+{
+    IO::out8(PIT_CTL, TIMER2_SELECT | WRITE_WORD | MODE_SQUARE_WAVE);
+    word timer_reload = BASE_FREQUENCY / frequency;
+
+    IO::out8(TIMER2_CTL, LSB(timer_reload));
+    IO::out8(TIMER2_CTL, MSB(timer_reload));
+
+    IO::out8(0x61, IO::in8(0x61) | 3);
+}
+
+void PCSpeaker::tone_off()
+{
+    IO::out8(0x61, IO::in8(0x61) & ~3);
+}

Kernel/Devices/PCSpeaker.h

@@ -0,0 +1,7 @@
+#pragma once
+
+class PCSpeaker {
+public:
+    static void tone_on(int frequency);
+    static void tone_off();
+};

Kernel/Makefile

@@ -49,6 +49,7 @@ KERNEL_OBJS = \
        Net/Routing.o \
        Net/NetworkTask.o \
        ProcessTracer.o \
+       Devices/PCSpeaker.o \
        File.o
 
 VFS_OBJS = \

Kernel/Scheduler.cpp

@@ -5,6 +5,7 @@
 #include <AK/TemporaryChange.h>
 #include <Kernel/Alarm.h>
 #include <Kernel/FileSystem/FileDescriptor.h>
+#include <Kernel/Devices/PCSpeaker.h>
 
 //#define LOG_EVERY_CONTEXT_SWITCH
 //#define SCHEDULER_DEBUG
@@ -30,6 +31,7 @@ Thread* g_last_fpu_thread;
 Thread* g_finalizer;
 static Process* s_colonel_process;
 qword g_uptime;
+static qword s_beep_timeout;
 
 struct TaskRedirectionData {
     word selector;
@@ -43,6 +45,12 @@ bool Scheduler::is_active()
     return s_active;
 }
 
+void Scheduler::beep()
+{
+    PCSpeaker::tone_on(440);
+    s_beep_timeout = g_uptime + 100;
+}
+
 bool Scheduler::pick_next()
 {
     ASSERT_INTERRUPTS_DISABLED();
@@ -395,6 +403,11 @@ void Scheduler::timer_tick(RegisterDump& regs)
 
     ++g_uptime;
 
+    if (s_beep_timeout && g_uptime > s_beep_timeout) {
+        PCSpeaker::tone_off();
+        s_beep_timeout = 0;
+    }
+
     if (current->tick())
         return;
 

Kernel/Scheduler.h

@@ -25,6 +25,7 @@ public:
     static void prepare_to_modify_tss(Thread&);
     static Process* colonel();
     static bool is_active();
+    static void beep();
 private:
     static void prepare_for_iret_to_new_process();
 };

Kernel/Syscall.cpp

@@ -60,6 +60,9 @@ static dword handle(RegisterDump& regs, dword function, dword arg1, dword arg2,
     case Syscall::SC_yield:
         Scheduler::yield();
         break;
+    case Syscall::SC_beep:
+        Scheduler::beep();
+        break;
     case Syscall::SC_donate:
         return current->process().sys$donate((int)arg1);
     case Syscall::SC_gettid:

Kernel/Syscall.h

@@ -103,6 +103,7 @@
     __ENUMERATE_SYSCALL(exit_thread) \
     __ENUMERATE_SYSCALL(mknod) \
     __ENUMERATE_SYSCALL(writev) \
+    __ENUMERATE_SYSCALL(beep) \
 
 
 namespace Syscall {

Kernel/i8253.cpp

@@ -37,26 +37,6 @@ asm(
     "    iret\n"
 );
 
-/* Timer related ports */
-#define TIMER0_CTL         0x40
-#define TIMER1_CTL         0x41
-#define TIMER2_CTL         0x42
-#define PIT_CTL            0x43
-
-/* Building blocks for PIT_CTL */
-#define TIMER0_SELECT      0x00
-#define TIMER1_SELECT      0x40
-#define TIMER2_SELECT      0x80
-
-#define MODE_COUNTDOWN     0x00
-#define MODE_ONESHOT       0x02
-#define MODE_RATE          0x04
-#define MODE_SQUARE_WAVE   0x06
-
-#define WRITE_WORD         0x30
-
-#define BASE_FREQUENCY     1193182
-
 static dword s_ticks_this_second;
 static dword s_seconds_since_boot;
 

Kernel/i8253.h

@@ -3,6 +3,25 @@
 #include <AK/Types.h>
 
 #define TICKS_PER_SECOND          1000
+/* Timer related ports */
+#define TIMER0_CTL         0x40
+#define TIMER1_CTL         0x41
+#define TIMER2_CTL         0x42
+#define PIT_CTL            0x43
+
+/* Building blocks for PIT_CTL */
+#define TIMER0_SELECT      0x00
+#define TIMER1_SELECT      0x40
+#define TIMER2_SELECT      0x80
+
+#define MODE_COUNTDOWN     0x00
+#define MODE_ONESHOT       0x02
+#define MODE_RATE          0x04
+#define MODE_SQUARE_WAVE   0x06
+
+#define WRITE_WORD         0x30
+
+#define BASE_FREQUENCY     1193182
 
 namespace PIT {
 

Kernel/run

@@ -14,7 +14,8 @@ elif [ "$1" = "qn" ]; then
         $SERENITY_EXTRA_QEMU_ARGS \
         -device e1000 \
         -kernel kernel \
-        -hda _fs_contents
+        -hda _fs_contents \
+        -soundhw pcspk
 elif [ "$1" = "qtap" ]; then
     # ./run qtap: qemu with tap
     sudo $SERENITY_QEMU_BIN -s -m $ram_size \
@@ -23,7 +24,8 @@ elif [ "$1" = "qtap" ]; then
         -netdev tap,ifname=tap0,id=br0 \
         -device e1000,netdev=br0 \
         -kernel kernel \
-        -hda _fs_contents
+        -hda _fs_contents \
+        -soundhw pcspk
 else
     # ./run: qemu with user networking
     $SERENITY_QEMU_BIN -s -m $ram_size \
@@ -32,6 +34,7 @@ else
         -netdev user,id=breh,hostfwd=tcp:127.0.0.1:8888-192.168.5.2:8888 \
         -device e1000,netdev=breh \
         -kernel kernel \
-        -hda _fs_contents
+        -hda _fs_contents \
+        -soundhw pcspk
 fi
 

LibC/unistd.cpp

@@ -475,4 +475,9 @@ int donate(int tid)
     __RETURN_WITH_ERRNO(rc, rc, -1);
 }
 
+void beep()
+{
+    syscall(SC_beep);
+}
+
 }

LibC/unistd.h

@@ -14,6 +14,7 @@ __BEGIN_DECLS
 
 extern char** environ;
 
+void beep();
 int systrace(pid_t);
 int gettid();
 int donate(int tid);

Shell/LineEditor.cpp

@@ -147,8 +147,11 @@ String LineEditor::get_line()
             }
 
             auto do_backspace = [&] {
-                if (m_cursor == 0)
+                if (m_cursor == 0) {
+                    fputc('\a', stdout);
+                    fflush(stdout);
                     return;
+                }
                 m_buffer.remove(m_cursor - 1);
                 --m_cursor;
                 putchar(8);