Kernel: Introduce the new Time management subsystem

This new subsystem includes better abstractions of how time will be
handled in the OS. We take advantage of the existing RTC timer to aid
in keeping time synchronized. This is standing in contrast to how we
handled time-keeping in the kernel, where the PIT was responsible for
that function in addition to update the scheduler about ticks.
With that new advantage, we can easily change the ticking dynamically
and still keep the time synchronized.

In the process context, we no longer use a fixed declaration of
TICKS_PER_SECOND, but we call the TimeManagement singleton class to
provide us the right value. This allows us to use dynamic ticking in
the future, a feature known as tickless kernel.

The scheduler no longer does by himself the calculation of real time
(Unix time), and just calls the TimeManagment singleton class to provide
the value.

Also, we can use 2 new boot arguments:
- the "time" boot argument accpets either the value "modern", or
  "legacy". If "modern" is specified, the time management subsystem will
  try to setup HPET. Otherwise, for "legacy" value, the time subsystem
  will revert to use the PIT & RTC, leaving HPET disabled.
  If this boot argument is not specified, the default pattern is to try
  to setup HPET.
- the "hpet" boot argumet accepts either the value "periodic" or
  "nonperiodic". If "periodic" is specified, the HPET will scan for
  periodic timers, and will assert if none are found. If only one is
  found, that timer will be assigned for the time-keeping task. If more
  than one is found, both time-keeping task & scheduler-ticking task
  will be assigned to periodic timers.
  If this boot argument is not specified, the default pattern is to try
  to scan for HPET periodic timers. This boot argument has no effect if
  HPET is disabled.

In hardware context, PIT & RealTimeClock classes are merely inheriting
from the HardwareTimer class, and they allow to use the old i8254 (PIT)
and RTC devices, managing them via IO ports. By default, the RTC will be
programmed to a frequency of 1024Hz. The PIT will be programmed to a
frequency close to 1000Hz.

About HPET, depending if we need to scan for periodic timers or not,
we try to set a frequency close to 1000Hz for the time-keeping timer
and scheduler-ticking timer. Also, if possible, we try to enable the
Legacy replacement feature of the HPET. This feature if exists,
instructs the chipset to disconnect both i8254 (PIT) and RTC.
This behavior is observable on QEMU, and was verified against the source
code:
https://github.com/qemu/qemu/commit/ce967e2f33861b0e17753f97fa4527b5943c94b6

The HPETComparator class is inheriting from HardwareTimer class, and is
responsible for an individual HPET comparator, which is essentially a
timer. Therefore, it needs to call the singleton HPET class to perform
HPET-related operations.

The new abstraction of Hardware timers brings an opportunity of more new
features in the foreseeable future. For example, we can change the
callback function of each hardware timer, thus it makes it possible to
swap missions between hardware timers, or to allow to use a hardware
timer for other temporary missions (e.g. calibrating the LAPIC timer,
measuring the CPU frequency, etc).

Kernel/Devices/PCSpeaker.cpp

@@ -26,7 +26,7 @@
 
 #include <Kernel/Arch/i386/CPU.h>
 #include <Kernel/Devices/PCSpeaker.h>
-#include <Kernel/Devices/PIT.h>
+#include <Kernel/Time/PIT.h>
 #include <LibBareMetal/IO.h>
 
 void PCSpeaker::tone_on(int frequency)

Kernel/Makefile

@@ -24,7 +24,12 @@ OBJS = \
     Interrupts/IRQHandler.o \
     Interrupts/SharedIRQHandler.o \
     CMOS.o \
-    Devices/PIT.o \
+    Time/PIT.o \
+    Time/TimeManagement.o \
+    Time/HardwareTimer.o \
+    Time/RTC.o \
+    Time/HPET.o \
+    Time/HPETComparator.o \
     Devices/BXVGADevice.o \
     Devices/BlockDevice.o \
     Devices/CharacterDevice.o \
@@ -48,7 +53,6 @@ OBJS = \
     Devices/SerialDevice.o \
     Devices/ZeroDevice.o \
     Devices/VMWareBackdoor.o \
-    Devices/HardwareTimer.o \
     DoubleBuffer.o \
     FileSystem/Custody.o \
     FileSystem/DevPtsFS.o \

Kernel/Process.cpp

@@ -37,7 +37,6 @@
 #include <Kernel/Devices/KeyboardDevice.h>
 #include <Kernel/Devices/NullDevice.h>
 #include <Kernel/Devices/PCSpeaker.h>
-#include <Kernel/Devices/PIT.h>
 #include <Kernel/Devices/RandomDevice.h>
 #include <Kernel/FileSystem/Custody.h>
 #include <Kernel/FileSystem/DevPtsFS.h>
@@ -67,6 +66,7 @@
 #include <Kernel/TTY/MasterPTY.h>
 #include <Kernel/TTY/TTY.h>
 #include <Kernel/Thread.h>
+#include <Kernel/Time/TimeManagement.h>
 #include <Kernel/VM/PageDirectory.h>
 #include <Kernel/VM/PrivateInodeVMObject.h>
 #include <Kernel/VM/PurgeableVMObject.h>
@@ -2105,13 +2105,13 @@ unsigned Process::sys$alarm(unsigned seconds)
     REQUIRE_PROMISE(stdio);
     unsigned previous_alarm_remaining = 0;
     if (m_alarm_deadline && m_alarm_deadline > g_uptime) {
-        previous_alarm_remaining = (m_alarm_deadline - g_uptime) / TICKS_PER_SECOND;
+        previous_alarm_remaining = (m_alarm_deadline - g_uptime) / TimeManagement::the().ticks_per_second();
     }
     if (!seconds) {
         m_alarm_deadline = 0;
         return previous_alarm_remaining;
     }
-    m_alarm_deadline = g_uptime + seconds * TICKS_PER_SECOND;
+    m_alarm_deadline = g_uptime + seconds * TimeManagement::the().ticks_per_second();
     return previous_alarm_remaining;
 }
 
@@ -2231,10 +2231,10 @@ int Process::sys$sleep(unsigned seconds)
     REQUIRE_PROMISE(stdio);
     if (!seconds)
         return 0;
-    u64 wakeup_time = Thread::current->sleep(seconds * TICKS_PER_SECOND);
+    u64 wakeup_time = Thread::current->sleep(seconds * TimeManagement::the().ticks_per_second());
     if (wakeup_time > g_uptime) {
         u32 ticks_left_until_original_wakeup_time = wakeup_time - g_uptime;
-        return ticks_left_until_original_wakeup_time / TICKS_PER_SECOND;
+        return ticks_left_until_original_wakeup_time / TimeManagement::the().ticks_per_second();
     }
     return 0;
 }
@@ -4268,8 +4268,12 @@ int Process::sys$clock_gettime(clockid_t clock_id, timespec* user_ts)
 
     switch (clock_id) {
     case CLOCK_MONOTONIC:
-        ts.tv_sec = g_uptime / TICKS_PER_SECOND;
-        ts.tv_nsec = (g_uptime % TICKS_PER_SECOND) * 1000000;
+        ts.tv_sec = TimeManagement::the().seconds_since_boot();
+        ts.tv_nsec = TimeManagement::the().ticks_this_second() * 1000000;
+        break;
+    case CLOCK_REALTIME:
+        ts.tv_sec = TimeManagement::the().epoch_time();
+        ts.tv_nsec = TimeManagement::the().ticks_this_second() * 1000000;
         break;
     default:
         return -EINVAL;
@@ -4322,8 +4326,8 @@ int Process::sys$clock_nanosleep(const Syscall::SC_clock_nanosleep_params* user_
 
                 timespec remaining_sleep;
                 memset(&remaining_sleep, 0, sizeof(timespec));
-                remaining_sleep.tv_sec = ticks_left / TICKS_PER_SECOND;
-                ticks_left -= remaining_sleep.tv_sec * TICKS_PER_SECOND;
+                remaining_sleep.tv_sec = ticks_left / TimeManagement::the().ticks_per_second();
+                ticks_left -= remaining_sleep.tv_sec * TimeManagement::the().ticks_per_second();
                 remaining_sleep.tv_nsec = ticks_left * 1000000;
                 copy_to_user(params.remaining_sleep, &remaining_sleep);
             }

Kernel/Scheduler.cpp

@@ -26,13 +26,13 @@
 
 #include <AK/QuickSort.h>
 #include <AK/TemporaryChange.h>
-#include <Kernel/Devices/PIT.h>
 #include <Kernel/FileSystem/FileDescription.h>
 #include <Kernel/Net/Socket.h>
 #include <Kernel/Process.h>
 #include <Kernel/Profiling.h>
 #include <Kernel/RTC.h>
 #include <Kernel/Scheduler.h>
+#include <Kernel/Time/TimeManagement.h>
 #include <Kernel/TimerQueue.h>
 
 //#define LOG_EVERY_CONTEXT_SWITCH
@@ -588,8 +588,8 @@ void Scheduler::timer_tick(const RegisterState& regs)
     ++g_uptime;
 
     timeval tv;
-    tv.tv_sec = RTC::boot_time() + PIT::the().seconds_since_boot();
-    tv.tv_usec = PIT::the().ticks_this_second() * 1000;
+    tv.tv_sec = TimeManagement::the().epoch_time();
+    tv.tv_usec = TimeManagement::the().ticks_this_second() * 1000;
     Process::update_info_page_timestamp(tv);
 
     if (Process::current->is_profiling()) {

Kernel/Time/HPET.cpp

@@ -0,0 +1,362 @@
+/*
+ * Copyright (c) 2020, Liav A. <liavalb@hotmail.co.il>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <Kernel/ACPI/ACPIParser.h>
+#include <Kernel/Interrupts/InterruptManagement.h>
+#include <Kernel/Time/HPET.h>
+#include <Kernel/Time/HPETComparator.h>
+#include <Kernel/Time/TimeManagement.h>
+#include <Kernel/VM/MemoryManager.h>
+
+namespace Kernel {
+
+#define ABSOLUTE_MAXIMUM_COUNTER_TICK_PERIOD 0x05F5E100
+#define NANOSECOND_PERIOD_TO_HERTZ(x) 1000000000 / x
+#define MEGAHERTZ_TO_HERTZ(x) (x / 1000000)
+
+//#define HPET_DEBUG
+
+namespace HPETFlags {
+enum class Attributes {
+    Counter64BitCapable = 1 << 13,
+    LegacyReplacementRouteCapable = 1 << 15
+};
+
+enum class Configuration {
+    Enable = 0x1,
+    LegacyReplacementRoute = 0x2
+};
+
+enum class TimerConfiguration : u32 {
+    InterruptType = 1 << 1,
+    InterruptEnable = 1 << 2,
+    TimerType = 1 << 3,
+    PeriodicInterruptCapable = 1 << 4,
+    Timer64BitsCapable = 1 << 5,
+    ValueSet = 1 << 6,
+    Force32BitMode = 1 << 7,
+    FSBInterruptEnable = 1 << 14,
+    FSBInterruptDelivery = 1 << 15
+};
+};
+
+struct [[gnu::packed]] TimerStructure
+{
+    u64 configuration_and_capability;
+    u64 comparator_value;
+    u64 fsb_interrupt_route;
+    u64 reserved;
+};
+
+struct [[gnu::packed]] HPETCapabilityRegister
+{
+    u8 revision_id;
+    u8 attributes;
+    u16 vendor_id;
+    u32 main_counter_tick_period;
+    u64 reserved;
+};
+
+struct [[gnu::packed]] HPETRegister
+{
+    u64 reg;
+    u64 reserved;
+};
+
+struct [[gnu::packed]] HPETRegistersBlock
+{
+    union {
+        volatile HPETCapabilityRegister capabilities; // Note: We must do a 32 bit access to offsets 0x0, or 0x4 only, according to HPET spec.
+        volatile HPETRegister raw_capabilites;
+    };
+    HPETRegister configuration;
+    HPETRegister interrupt_status;
+    u8 reserved[0xF0 - 48];
+    HPETRegister main_counter_value;
+    TimerStructure timers[3];
+    u8 reserved2[0x400 - 0x160];
+};
+
+static HPET* s_hpet;
+static bool hpet_initialized { false };
+
+bool HPET::initialized()
+{
+    return hpet_initialized;
+}
+
+HPET& HPET::the()
+{
+    ASSERT(HPET::initialized());
+    ASSERT(s_hpet != nullptr);
+    return *s_hpet;
+}
+
+bool HPET::test_and_initialize()
+{
+    ASSERT(!HPET::initialized());
+    hpet_initialized = true;
+    auto hpet = ACPI::Parser::the().find_table("HPET");
+    if (hpet.is_null())
+        return false;
+    klog() << "HPET @ " << hpet;
+
+    auto region = MM.allocate_kernel_region(hpet.page_base(), (PAGE_SIZE * 2), "HPET Initialization", Region::Access::Read);
+    auto* sdt = (volatile ACPI::Structures::HPET*)region->vaddr().offset(hpet.offset_in_page()).as_ptr();
+
+    // Note: HPET is only usable from System Memory
+    ASSERT(sdt->event_timer_block.address_space == (u8)ACPI::GenericAddressStructure::AddressSpace::SystemMemory);
+
+    if (TimeManagement::is_hpet_periodic_mode_allowed()) {
+        if (!check_for_exisiting_periodic_timers()) {
+            dbg() << "HPET: No periodic capable timers";
+            return false;
+        }
+    }
+    s_hpet = new HPET(PhysicalAddress(hpet));
+    return true;
+}
+
+bool HPET::check_for_exisiting_periodic_timers()
+{
+    auto hpet = ACPI::Parser::the().find_table("HPET");
+    if (hpet.is_null())
+        return false;
+    auto region = MM.allocate_kernel_region(hpet.page_base(), (PAGE_SIZE * 2), "HPET Initialization", Region::Access::Read);
+    auto* sdt = (volatile ACPI::Structures::HPET*)region->vaddr().offset(hpet.offset_in_page()).as_ptr();
+
+    ASSERT(sdt->event_timer_block.address_space == 0);
+
+    auto p_block = PhysicalAddress(sdt->event_timer_block.address);
+    auto block_region = MM.allocate_kernel_region(p_block, (PAGE_SIZE * 2), "HPET Initialization", Region::Access::Read);
+    auto* registers = (volatile HPETRegistersBlock*)block_region->vaddr().offset(p_block.offset_in_page()).as_ptr();
+
+    auto* capabilities_register = (volatile HPETCapabilityRegister*)&registers->capabilities;
+    size_t timers_count = (capabilities_register->attributes & 0x1f) + 1;
+    for (size_t index = 0; index < timers_count; index++) {
+        if (registers->timers[index].configuration_and_capability & (u32)HPETFlags::TimerConfiguration::PeriodicInterruptCapable)
+            return true;
+    }
+    return false;
+}
+
+const FixedArray<RefPtr<HPETComparator>>& HPET::comparators() const
+{
+    return m_comparators;
+}
+
+void HPET::global_disable()
+{
+    auto* registers_block = (volatile HPETRegistersBlock*)m_hpet_mmio_region->vaddr().offset(m_physical_acpi_hpet_registers.offset_in_page()).as_ptr();
+    registers_block->configuration.reg &= ~(u32)HPETFlags::Configuration::Enable;
+}
+void HPET::global_enable()
+{
+    auto* registers_block = (volatile HPETRegistersBlock*)m_hpet_mmio_region->vaddr().offset(m_physical_acpi_hpet_registers.offset_in_page()).as_ptr();
+    registers_block->configuration.reg |= (u32)HPETFlags::Configuration::Enable;
+}
+
+void HPET::set_periodic_comparator_value(const HPETComparator& comparator, u64 value)
+{
+    disable(comparator);
+    ASSERT(comparator.is_periodic());
+    ASSERT(comparator.comparator_number() <= m_comparators.size());
+    auto* registers_block = (volatile HPETRegistersBlock*)m_hpet_mmio_region->vaddr().offset(m_physical_acpi_hpet_registers.offset_in_page()).as_ptr();
+    registers_block->timers[comparator.comparator_number()].configuration_and_capability |= (u32)HPETFlags::TimerConfiguration::ValueSet;
+    registers_block->timers[comparator.comparator_number()].comparator_value = value;
+    enable(comparator);
+}
+
+void HPET::set_non_periodic_comparator_value(const HPETComparator& comparator, u64 value)
+{
+    ASSERT_INTERRUPTS_DISABLED();
+    ASSERT(!comparator.is_periodic());
+    ASSERT(comparator.comparator_number() <= m_comparators.size());
+    auto* registers_block = (volatile HPETRegistersBlock*)m_hpet_mmio_region->vaddr().offset(m_physical_acpi_hpet_registers.offset_in_page()).as_ptr();
+    registers_block->timers[comparator.comparator_number()].comparator_value = main_counter_value() + value;
+}
+void HPET::enable_periodic_interrupt(const HPETComparator& comparator)
+{
+#ifdef HPET_DEBUG
+    klog() << "HPET: Set comparator " << comparator.comparator_number() << " to be periodic.";
+#endif
+    disable(comparator);
+    ASSERT(comparator.comparator_number() <= m_comparators.size());
+    auto* registers_block = (volatile HPETRegistersBlock*)m_hpet_mmio_region->vaddr().offset(m_physical_acpi_hpet_registers.offset_in_page()).as_ptr();
+    ASSERT(registers_block->timers[comparator.comparator_number()].configuration_and_capability & (u32)HPETFlags::TimerConfiguration::PeriodicInterruptCapable);
+    registers_block->timers[comparator.comparator_number()].configuration_and_capability |= (u32)HPETFlags::TimerConfiguration::TimerType;
+    enable(comparator);
+}
+void HPET::disable_periodic_interrupt(const HPETComparator& comparator)
+{
+#ifdef HPET_DEBUG
+    klog() << "HPET: Disable periodic interrupt in comparator " << comparator.comparator_number() << ".";
+#endif
+    disable(comparator);
+    ASSERT(comparator.comparator_number() <= m_comparators.size());
+    auto* registers_block = (volatile HPETRegistersBlock*)m_hpet_mmio_region->vaddr().offset(m_physical_acpi_hpet_registers.offset_in_page()).as_ptr();
+    ASSERT(registers_block->timers[comparator.comparator_number()].configuration_and_capability & (u32)HPETFlags::TimerConfiguration::PeriodicInterruptCapable);
+    registers_block->timers[comparator.comparator_number()].configuration_and_capability &= ~(u32)HPETFlags::TimerConfiguration::TimerType;
+    enable(comparator);
+}
+
+void HPET::disable(const HPETComparator& comparator)
+{
+#ifdef HPET_DEBUG
+    klog() << "HPET: Disable comparator " << comparator.comparator_number() << ".";
+#endif
+    ASSERT(comparator.comparator_number() <= m_comparators.size());
+    auto* registers_block = (volatile HPETRegistersBlock*)m_hpet_mmio_region->vaddr().offset(m_physical_acpi_hpet_registers.offset_in_page()).as_ptr();
+    registers_block->timers[comparator.comparator_number()].configuration_and_capability &= ~(u32)HPETFlags::TimerConfiguration::InterruptEnable;
+}
+void HPET::enable(const HPETComparator& comparator)
+{
+#ifdef HPET_DEBUG
+    klog() << "HPET: Enable comparator " << comparator.comparator_number() << ".";
+#endif
+    ASSERT(comparator.comparator_number() <= m_comparators.size());
+    auto* registers_block = (volatile HPETRegistersBlock*)m_hpet_mmio_region->vaddr().offset(m_physical_acpi_hpet_registers.offset_in_page()).as_ptr();
+    registers_block->timers[comparator.comparator_number()].configuration_and_capability |= (u32)HPETFlags::TimerConfiguration::InterruptEnable;
+}
+
+u64 HPET::main_counter_value() const
+{
+    auto* registers_block = (const volatile HPETRegistersBlock*)m_hpet_mmio_region->vaddr().offset(m_physical_acpi_hpet_registers.offset_in_page()).as_ptr();
+    return registers_block->main_counter_value.reg;
+}
+u64 HPET::frequency() const
+{
+    return m_frequency;
+}
+
+Vector<unsigned> HPET::capable_interrupt_numbers(const HPETComparator& comparator)
+{
+    ASSERT(comparator.comparator_number() <= m_comparators.size());
+    Vector<unsigned> capable_interrupts;
+    auto* registers_block = (volatile HPETRegistersBlock*)m_hpet_mmio_region->vaddr().offset(m_physical_acpi_hpet_registers.offset_in_page()).as_ptr();
+    auto* comparator_registers = (const volatile TimerStructure*)&registers_block->timers[comparator.comparator_number()];
+    u32 interrupt_bitfield = comparator_registers->configuration_and_capability >> 32;
+    for (size_t index = 0; index < 32; index++) {
+        if (interrupt_bitfield & 1)
+            capable_interrupts.append(index);
+        interrupt_bitfield >>= 1;
+    }
+    return capable_interrupts;
+}
+
+Vector<unsigned> HPET::capable_interrupt_numbers(u8 comparator_number)
+{
+    ASSERT(comparator_number <= m_comparators.size());
+    Vector<unsigned> capable_interrupts;
+    auto* registers_block = (volatile HPETRegistersBlock*)m_hpet_mmio_region->vaddr().offset(m_physical_acpi_hpet_registers.offset_in_page()).as_ptr();
+    auto* comparator_registers = (const volatile TimerStructure*)&registers_block->timers[comparator_number];
+    u32 interrupt_bitfield = comparator_registers->configuration_and_capability >> 32;
+    for (size_t index = 0; index < 32; index++) {
+        if (interrupt_bitfield & 1)
+            capable_interrupts.append(index);
+        interrupt_bitfield >>= 1;
+    }
+    return capable_interrupts;
+}
+
+void HPET::set_comparator_irq_vector(u8 comparator_number, u8 irq_vector)
+{
+    ASSERT(comparator_number <= m_comparators.size());
+    auto* registers_block = (volatile HPETRegistersBlock*)m_hpet_mmio_region->vaddr().offset(m_physical_acpi_hpet_registers.offset_in_page()).as_ptr();
+    auto* comparator_registers = (volatile TimerStructure*)&registers_block->timers[comparator_number];
+    comparator_registers->configuration_and_capability |= (irq_vector << 9);
+}
+
+bool HPET::is_periodic_capable(u8 comparator_number) const
+{
+    ASSERT(comparator_number <= m_comparators.size());
+    auto* registers_block = (volatile HPETRegistersBlock*)m_hpet_mmio_region->vaddr().offset(m_physical_acpi_hpet_registers.offset_in_page()).as_ptr();
+    auto* comparator_registers = (const volatile TimerStructure*)&registers_block->timers[comparator_number];
+    return comparator_registers->configuration_and_capability & (u32)HPETFlags::TimerConfiguration::PeriodicInterruptCapable;
+}
+
+void HPET::set_comparators_to_optimal_interrupt_state(size_t)
+{
+    // FIXME: Implement this method for allowing to use HPET timers 2-31...
+    ASSERT_NOT_REACHED();
+}
+
+PhysicalAddress HPET::find_acpi_hept_registers_block()
+{
+    auto region = MM.allocate_kernel_region(m_physical_acpi_hpet_table.page_base(), (PAGE_SIZE * 2), "HPET Initialization", Region::Access::Read);
+    auto* sdt = (ACPI::Structures::HPET*)region->vaddr().offset(m_physical_acpi_hpet_table.offset_in_page()).as_ptr();
+    ASSERT(sdt->event_timer_block.address_space == (u8)ACPI::GenericAddressStructure::AddressSpace::SystemMemory);
+    return PhysicalAddress(sdt->event_timer_block.address);
+}
+u64 HPET::calculate_ticks_in_nanoseconds() const
+{
+    auto* registers_block = (const volatile HPETRegistersBlock*)m_hpet_mmio_region->vaddr().offset(m_physical_acpi_hpet_registers.offset_in_page()).as_ptr();
+    return ABSOLUTE_MAXIMUM_COUNTER_TICK_PERIOD / registers_block->capabilities.main_counter_tick_period;
+}
+HPET::HPET(PhysicalAddress acpi_hpet)
+    : m_physical_acpi_hpet_table(acpi_hpet)
+    , m_physical_acpi_hpet_registers(find_acpi_hept_registers_block())
+    , m_hpet_mmio_region(MM.allocate_kernel_region(m_physical_acpi_hpet_registers.page_base(), PAGE_SIZE, "HPET MMIO", Region::Access::Read | Region::Access::Write))
+{
+    auto region = MM.allocate_kernel_region(m_physical_acpi_hpet_table.page_base(), (PAGE_SIZE * 2), "HPET Initialization", Region::Access::Read);
+    auto* sdt = (volatile ACPI::Structures::HPET*)region->vaddr().offset(m_physical_acpi_hpet_table.offset_in_page()).as_ptr();
+    m_vendor_id = sdt->pci_vendor_id;
+    m_minimum_tick = sdt->mininum_clock_tick;
+    klog() << "HPET: Minimum clock tick - " << m_minimum_tick;
+
+    auto* registers_block = (volatile HPETRegistersBlock*)m_hpet_mmio_region->vaddr().offset(m_physical_acpi_hpet_registers.offset_in_page()).as_ptr();
+
+    // Note: We must do a 32 bit access to offsets 0x0, or 0x4 only.
+    size_t timers_count = ((registers_block->raw_capabilites.reg >> 8) & 0x1f) + 1;
+    klog() << "HPET: Timers count - " << timers_count;
+    ASSERT(timers_count >= 2);
+    m_comparators.resize(timers_count);
+    auto* capabilities_register = (const volatile HPETCapabilityRegister*)&registers_block->raw_capabilites.reg;
+
+    global_disable();
+
+    m_frequency = NANOSECOND_PERIOD_TO_HERTZ(calculate_ticks_in_nanoseconds());
+    klog() << "HPET: frequency " << m_frequency << " Hz (" << MEGAHERTZ_TO_HERTZ(m_frequency) << " MHz)";
+    ASSERT(capabilities_register->main_counter_tick_period <= ABSOLUTE_MAXIMUM_COUNTER_TICK_PERIOD);
+
+    // Reset the counter, just in case...
+    registers_block->main_counter_value.reg = 0;
+    if (registers_block->raw_capabilites.reg & (u32)HPETFlags::Attributes::LegacyReplacementRouteCapable)
+        registers_block->configuration.reg |= (u32)HPETFlags::Configuration::LegacyReplacementRoute;
+
+    for (size_t index = 0; index < m_comparators.size(); index++) {
+        bool periodic = is_periodic_capable(index);
+        if (index == 0) {
+            m_comparators[index] = HPETComparator::create(index, 0, periodic);
+        }
+        if (index == 1) {
+            m_comparators[index] = HPETComparator::create(index, 8, periodic);
+        }
+    }
+
+    global_enable();
+}
+}

Kernel/Time/HPET.h

@@ -0,0 +1,90 @@
+/*
+ * Copyright (c) 2020, Liav A. <liavalb@hotmail.co.il>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include <AK/FixedArray.h>
+#include <AK/OwnPtr.h>
+#include <AK/Types.h>
+#include <AK/Vector.h>
+#include <Kernel/Time/HPET.h>
+#include <Kernel/VM/Region.h>
+#include <LibBareMetal/Memory/PhysicalAddress.h>
+
+namespace Kernel {
+
+class HPETComparator;
+class HPET {
+public:
+    static bool initialized();
+    static bool test_and_initialize();
+    static bool check_for_exisiting_periodic_timers();
+    static HPET& the();
+
+    u64 main_counter_value() const;
+    u64 frequency() const;
+
+    const FixedArray<RefPtr<HPETComparator>>& comparators() const;
+    void disable(const HPETComparator&);
+    void enable(const HPETComparator&);
+
+    void set_periodic_comparator_value(const HPETComparator& comparator, u64 value);
+    void set_non_periodic_comparator_value(const HPETComparator& comparator, u64 value);
+
+    void set_comparator_irq_vector(u8 comparator_number, u8 irq_vector);
+
+    void enable_periodic_interrupt(const HPETComparator& comparator);
+    void disable_periodic_interrupt(const HPETComparator& comparator);
+
+    Vector<unsigned> capable_interrupt_numbers(u8 comparator_number);
+    Vector<unsigned> capable_interrupt_numbers(const HPETComparator&);
+
+private:
+    void global_disable();
+    void global_enable();
+
+    bool is_periodic_capable(u8 comparator_number) const;
+    void set_comparators_to_optimal_interrupt_state(size_t timers_count);
+
+    u64 calculate_ticks_in_nanoseconds() const;
+
+    PhysicalAddress find_acpi_hept_registers_block();
+    explicit HPET(PhysicalAddress acpi_hpet);
+    PhysicalAddress m_physical_acpi_hpet_table;
+    PhysicalAddress m_physical_acpi_hpet_registers;
+    OwnPtr<Region> m_hpet_mmio_region;
+
+    u64 m_main_counter_clock_period { 0 };
+    u16 m_vendor_id;
+    u16 m_minimum_tick;
+    u64 m_frequency;
+    u8 m_revision_id;
+    bool counter_is_64_bit_capable : 1;
+    bool legacy_replacement_route_capable : 1;
+
+    FixedArray<RefPtr<HPETComparator>> m_comparators;
+};
+}

Kernel/Time/HPETComparator.cpp

@@ -0,0 +1,126 @@
+/*
+ * Copyright (c) 2020, Liav A. <liavalb@hotmail.co.il>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <Kernel/Assertions.h>
+#include <Kernel/Time/HPETComparator.h>
+#include <Kernel/Time/TimeManagement.h>
+
+//#define HPET_COMPARATOR_DEBUG
+
+namespace Kernel {
+
+NonnullRefPtr<HPETComparator> HPETComparator::create(u8 number, u8 irq, bool periodic_capable)
+{
+    return adopt(*new HPETComparator(number, irq, periodic_capable, [](const RegisterState& regs) { TimeManagement::stale_function(regs); }));
+}
+
+HPETComparator::HPETComparator(u8 number, u8 irq, bool periodic_capable, Function<void(const RegisterState&)> callback)
+    : HardwareTimer(irq, move(callback))
+    , m_periodic(false)
+    , m_periodic_capable(periodic_capable)
+    , m_comparator_number(number)
+{
+}
+
+void HPETComparator::set_periodic()
+{
+    ASSERT(m_periodic_capable);
+    HPET::the().enable_periodic_interrupt(*this);
+    m_periodic = true;
+}
+void HPETComparator::set_non_periodic()
+{
+    ASSERT(m_periodic_capable);
+    HPET::the().disable_periodic_interrupt(*this);
+    m_periodic = false;
+}
+
+void HPETComparator::handle_irq(const RegisterState& regs)
+{
+    HardwareTimer::handle_irq(regs);
+    if (!is_periodic())
+        set_new_countdown();
+}
+
+void HPETComparator::set_new_countdown()
+{
+    ASSERT_INTERRUPTS_DISABLED();
+    ASSERT(m_frequency <= HPET::the().frequency());
+    HPET::the().set_non_periodic_comparator_value(*this, HPET::the().frequency() / m_frequency);
+}
+
+size_t HPETComparator::ticks_per_second() const
+{
+    return m_frequency;
+}
+
+void HPETComparator::reset_to_default_ticks_per_second()
+{
+    ASSERT(is_capable_of_frequency(OPTIMAL_TICKS_PER_SECOND_RATE));
+    m_frequency = OPTIMAL_TICKS_PER_SECOND_RATE;
+    if (!is_periodic())
+        set_new_countdown();
+    else
+        try_to_set_frequency(m_frequency);
+}
+bool HPETComparator::try_to_set_frequency(size_t frequency)
+{
+    InterruptDisabler disabler;
+    if (!is_capable_of_frequency(frequency))
+        return false;
+    disable_irq();
+    auto hpet_frequency = HPET::the().frequency();
+    ASSERT(frequency <= hpet_frequency);
+#ifdef HPET_COMPARATOR_DEBUG
+    dbg() << "HPET Comparator: Max frequency - " << hpet_frequency << " Hz, want to set " << frequency << " Hz";
+#endif
+    if (is_periodic())
+        HPET::the().set_periodic_comparator_value(*this, hpet_frequency / frequency);
+    else {
+        HPET::the().set_non_periodic_comparator_value(*this, hpet_frequency / frequency);
+        HPET::the().enable(*this);
+    }
+    m_frequency = frequency;
+    enable_irq();
+    return true;
+}
+bool HPETComparator::is_capable_of_frequency(size_t frequency) const
+{
+    if (frequency > HPET::the().frequency())
+        return false;
+    if ((HPET::the().frequency() % frequency) != 0)
+        return false;
+    return true;
+}
+size_t HPETComparator::calculate_nearest_possible_frequency(size_t frequency) const
+{
+    if (frequency >= HPET::the().frequency())
+        return HPET::the().frequency();
+    // FIXME: Use better math here
+    return (frequency + (HPET::the().frequency() % frequency));
+}
+
+}

Kernel/Time/HPETComparator.h

@@ -0,0 +1,67 @@
+/*
+ * Copyright (c) 2020, Liav A. <liavalb@hotmail.co.il>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include <AK/Function.h>
+#include <AK/Types.h>
+#include <Kernel/Time/HPET.h>
+#include <Kernel/Time/HardwareTimer.h>
+
+namespace Kernel {
+class HPETComparator final : public HardwareTimer {
+    friend class HPET;
+
+public:
+    static NonnullRefPtr<HPETComparator> create(u8 number, u8 irq, bool periodic_capable);
+
+    virtual HardwareTimerType timer_type() const override { return HardwareTimerType::HighPrecisionEventTimer; }
+    virtual const char* model() const override { return "HPET"; }
+
+    u8 comparator_number() const { return m_comparator_number; }
+
+    virtual size_t ticks_per_second() const override;
+
+    virtual bool is_periodic() const override { return m_periodic; }
+    virtual bool is_periodic_capable() const override { return m_periodic_capable; }
+    virtual void set_periodic() override;
+    virtual void set_non_periodic() override;
+
+    virtual void reset_to_default_ticks_per_second() override;
+    virtual bool try_to_set_frequency(size_t frequency) override;
+    virtual bool is_capable_of_frequency(size_t frequency) const override;
+    virtual size_t calculate_nearest_possible_frequency(size_t frequency) const override;
+
+private:
+    void set_new_countdown();
+    virtual void handle_irq(const RegisterState&) override;
+    HPETComparator(u8 number, u8 irq, bool periodic_capable, Function<void(const RegisterState&)> callback);
+    bool m_periodic : 1;
+    bool m_periodic_capable : 1;
+    bool m_edge_triggered : 1;
+    u8 m_comparator_number { 0 };
+};
+}

Kernel/Time/HardwareTimer.cpp

@@ -0,0 +1,54 @@
+/*
+ * Copyright (c) 2020, Liav A. <liavalb@hotmail.co.il>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <Kernel/Time/HardwareTimer.h>
+#include <Kernel/Time/TimeManagement.h>
+
+namespace Kernel {
+
+HardwareTimer::HardwareTimer(u8 irq_number, Function<void(const RegisterState&)> callback)
+    : IRQHandler(irq_number)
+    , m_function_to_call(move(callback))
+{
+}
+void HardwareTimer::handle_irq(const RegisterState& regs)
+{
+    m_function_to_call(regs);
+}
+const char* HardwareTimer::purpose() const
+{
+    if (TimeManagement::the().is_system_timer(*this))
+        return "System Timer";
+    return model();
+}
+void HardwareTimer::change_function(Function<void(const RegisterState&)> callback)
+{
+    disable_irq();
+    m_function_to_call = move(callback);
+    enable_irq();
+}
+
+}

Kernel/Time/HardwareTimer.h

@@ -0,0 +1,72 @@
+/*
+ * Copyright (c) 2020, Liav A. <liavalb@hotmail.co.il>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include <AK/Function.h>
+#include <AK/RefCounted.h>
+#include <AK/String.h>
+#include <Kernel/Interrupts/IRQHandler.h>
+#include <Kernel/Time/TimeManagement.h>
+
+namespace Kernel {
+
+enum class HardwareTimerType {
+    i8253 = 0x1,                  /* PIT */
+    RTC = 0x2,                    /* Real Time Clock */
+    HighPrecisionEventTimer = 0x3 /* also known as IA-PC HPET */
+};
+
+class HardwareTimer : public RefCounted<HardwareTimer>
+    , public IRQHandler {
+public:
+    virtual HardwareTimerType timer_type() const = 0;
+    virtual const char* model() const = 0;
+    virtual const char* purpose() const override;
+
+    virtual void change_function(Function<void(const RegisterState&)>);
+    virtual size_t ticks_per_second() const = 0;
+
+    virtual bool is_periodic() const = 0;
+    virtual bool is_periodic_capable() const = 0;
+    virtual void set_periodic() = 0;
+    virtual void set_non_periodic() = 0;
+
+    virtual void reset_to_default_ticks_per_second() = 0;
+    virtual bool try_to_set_frequency(size_t frequency) = 0;
+    virtual bool is_capable_of_frequency(size_t frequency) const = 0;
+    virtual size_t calculate_nearest_possible_frequency(size_t frequency) const = 0;
+
+protected:
+    HardwareTimer(u8 irq_number, Function<void(const RegisterState&)>);
+    //^IRQHandler
+    virtual void handle_irq(const RegisterState&) override;
+    u64 m_frequency { OPTIMAL_TICKS_PER_SECOND_RATE };
+
+private:
+    Function<void(const RegisterState&)> m_function_to_call;
+};
+}

Kernel/Time/PIT.cpp

@@ -0,0 +1,108 @@
+/*
+ * Copyright (c) 2020, Liav A. <liavalb@hotmail.co.il>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <Kernel/Arch/i386/CPU.h>
+#include <Kernel/Interrupts/PIC.h>
+#include <Kernel/Scheduler.h>
+#include <Kernel/Thread.h>
+#include <Kernel/Time/PIT.h>
+#include <Kernel/Time/TimeManagement.h>
+#include <LibBareMetal/IO.h>
+
+#define IRQ_TIMER 0
+namespace Kernel {
+
+NonnullRefPtr<PIT> PIT::initialize(Function<void(const RegisterState&)> callback)
+{
+    return adopt(*new PIT(move(callback)));
+}
+
+inline static void reset_countdown(u16 timer_reload)
+{
+    IO::out8(PIT_CTL, TIMER0_SELECT | WRITE_WORD | MODE_COUNTDOWN);
+    IO::out8(TIMER0_CTL, LSB(timer_reload));
+    IO::out8(TIMER0_CTL, MSB(timer_reload));
+}
+
+PIT::PIT(Function<void(const RegisterState&)> callback)
+    : HardwareTimer(IRQ_TIMER, move(callback))
+    , m_periodic(true)
+{
+    IO::out8(PIT_CTL, TIMER0_SELECT | WRITE_WORD | MODE_SQUARE_WAVE);
+
+    klog() << "PIT: " << OPTIMAL_TICKS_PER_SECOND_RATE << " Hz, square wave (" << String::format("%x", BASE_FREQUENCY / OPTIMAL_TICKS_PER_SECOND_RATE) << ")";
+    reset_to_default_ticks_per_second();
+    enable_irq();
+}
+
+size_t PIT::ticks_per_second() const
+{
+    return m_frequency;
+}
+
+void PIT::set_periodic()
+{
+    // FIXME: Implement it...
+    ASSERT_NOT_REACHED();
+}
+void PIT::set_non_periodic()
+{
+    // FIXME: Implement it...
+    ASSERT_NOT_REACHED();
+}
+
+void PIT::reset_to_default_ticks_per_second()
+{
+    InterruptDisabler disabler;
+    bool success = try_to_set_frequency(OPTIMAL_TICKS_PER_SECOND_RATE);
+    ASSERT(success);
+}
+
+bool PIT::try_to_set_frequency(size_t frequency)
+{
+    InterruptDisabler disabler;
+    if (!is_capable_of_frequency(frequency))
+        return false;
+    disable_irq();
+    size_t reload_value = BASE_FREQUENCY / frequency;
+    IO::out8(TIMER0_CTL, LSB(reload_value));
+    IO::out8(TIMER0_CTL, MSB(reload_value));
+    m_frequency = frequency;
+    enable_irq();
+    return true;
+}
+bool PIT::is_capable_of_frequency(size_t frequency) const
+{
+    ASSERT(frequency != 0);
+    return frequency <= BASE_FREQUENCY;
+}
+size_t PIT::calculate_nearest_possible_frequency(size_t frequency) const
+{
+    ASSERT(frequency != 0);
+    return frequency;
+}
+
+}

Kernel/Time/PIT.h

@@ -0,0 +1,76 @@
+/*
+ * Copyright (c) 2020, Liav A. <liavalb@hotmail.co.il>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include <AK/NonnullRefPtr.h>
+#include <AK/Types.h>
+#include <Kernel/Time/HardwareTimer.h>
+
+namespace Kernel {
+
+/* 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
+
+class PIT final : public HardwareTimer {
+public:
+    static NonnullRefPtr<PIT> initialize(Function<void(const RegisterState&)>);
+    virtual HardwareTimerType timer_type() const override { return HardwareTimerType::i8253; }
+    virtual const char* model() const override { return "i8254"; }
+    virtual size_t ticks_per_second() const override;
+
+    virtual bool is_periodic() const override { return m_periodic; }
+    virtual bool is_periodic_capable() const override { return true; }
+    virtual void set_periodic() override;
+    virtual void set_non_periodic() override;
+
+    virtual void reset_to_default_ticks_per_second() override;
+    virtual bool try_to_set_frequency(size_t frequency) override;
+    virtual bool is_capable_of_frequency(size_t frequency) const override;
+    virtual size_t calculate_nearest_possible_frequency(size_t frequency) const override;
+
+private:
+    explicit PIT(Function<void(const RegisterState&)>);
+    bool m_periodic { true };
+};
+}

Kernel/Time/RTC.cpp

@@ -0,0 +1,109 @@
+/*
+ * Copyright (c) 2020, Liav A. <liavalb@hotmail.co.il>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <Kernel/Arch/i386/CPU.h>
+#include <Kernel/CMOS.h>
+#include <Kernel/Time/RTC.h>
+#include <Kernel/Time/TimeManagement.h>
+#include <LibBareMetal/IO.h>
+
+namespace Kernel {
+#define IRQ_TIMER 8
+#define MAX_FREQUENCY 8000
+
+NonnullRefPtr<RealTimeClock> RealTimeClock::create(Function<void(const RegisterState&)> callback)
+{
+    return adopt(*new RealTimeClock(move(callback)));
+}
+RealTimeClock::RealTimeClock(Function<void(const RegisterState&)> callback)
+    : HardwareTimer(IRQ_TIMER, move(callback))
+{
+    InterruptDisabler disabler;
+    NonMaskableInterruptDisabler nmi_disabler;
+    enable_irq();
+    CMOS::write(0x8B, CMOS::read(0xB) | 0x40);
+    reset_to_default_ticks_per_second();
+}
+void RealTimeClock::handle_irq(const RegisterState& regs)
+{
+    HardwareTimer::handle_irq(regs);
+    CMOS::read(0x8C);
+}
+
+size_t RealTimeClock::ticks_per_second() const
+{
+    return m_frequency;
+}
+
+void RealTimeClock::reset_to_default_ticks_per_second()
+{
+    InterruptDisabler disabler;
+    bool success = try_to_set_frequency(1024);
+    ASSERT(success);
+}
+
+// FIXME: This is a quick & dirty log base 2 with a paramater. Please provide something better in the future.
+static int quick_log2(size_t number)
+{
+    int count = 0;
+    while (number >>= 1)
+        count++;
+    return count;
+}
+
+bool RealTimeClock::try_to_set_frequency(size_t frequency)
+{
+    InterruptDisabler disabler;
+    if (!is_capable_of_frequency(frequency))
+        return false;
+    disable_irq();
+    u8 previous_rate = CMOS::read(0x8A);
+    u8 rate = quick_log2(32768 / frequency) + 1;
+    dbg() << "RTC: Set rate to " << rate;
+    CMOS::write(0x8A, (previous_rate & 0xF0) | rate);
+    m_frequency = frequency;
+    dbg() << "RTC: Set frequency to " << frequency << " Hz";
+    enable_irq();
+    return true;
+}
+bool RealTimeClock::is_capable_of_frequency(size_t frequency) const
+{
+    ASSERT(frequency != 0);
+    if (frequency > MAX_FREQUENCY)
+        return false;
+    if (32768 % frequency)
+        return false;
+
+    u16 divider = 32768 / frequency;
+    return (divider <= 16384 && divider >= 4); // Frequency can be in range of 2 Hz to 8 KHz
+}
+size_t RealTimeClock::calculate_nearest_possible_frequency(size_t frequency) const
+{
+    ASSERT(frequency != 0);
+    return frequency;
+}
+
+}

Kernel/Time/RTC.h

@@ -0,0 +1,55 @@
+/*
+ * Copyright (c) 2020, Liav A. <liavalb@hotmail.co.il>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include <AK/NonnullRefPtr.h>
+#include <Kernel/RTC.h>
+#include <Kernel/Time/HardwareTimer.h>
+
+namespace Kernel {
+class RealTimeClock final : public HardwareTimer {
+public:
+    static NonnullRefPtr<RealTimeClock> create(Function<void(const RegisterState&)> callback);
+    virtual HardwareTimerType timer_type() const override { return HardwareTimerType::RTC; }
+    virtual const char* model() const override { return "Real Time Clock"; }
+    virtual size_t ticks_per_second() const override;
+
+    virtual bool is_periodic() const override { return true; }
+    virtual bool is_periodic_capable() const override { return true; }
+    virtual void set_periodic() override {}
+    virtual void set_non_periodic() override {}
+
+    virtual void reset_to_default_ticks_per_second() override;
+    virtual bool try_to_set_frequency(size_t frequency) override;
+    virtual bool is_capable_of_frequency(size_t frequency) const override;
+    virtual size_t calculate_nearest_possible_frequency(size_t frequency) const override;
+
+private:
+    explicit RealTimeClock(Function<void(const RegisterState&)> callback);
+    virtual void handle_irq(const RegisterState&) override;
+};
+}

Kernel/Time/TimeManagement.cpp

@@ -0,0 +1,261 @@
+/*
+ * Copyright (c) 2020, Liav A. <liavalb@hotmail.co.il>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <Kernel/ACPI/ACPIParser.h>
+#include <Kernel/KParams.h>
+#include <Kernel/Scheduler.h>
+#include <Kernel/Time/HPET.h>
+#include <Kernel/Time/HPETComparator.h>
+#include <Kernel/Time/HardwareTimer.h>
+#include <Kernel/Time/PIT.h>
+#include <Kernel/Time/RTC.h>
+#include <Kernel/Time/TimeManagement.h>
+#include <Kernel/VM/MemoryManager.h>
+
+//#define TIME_DEBUG
+
+namespace Kernel {
+
+static TimeManagement* s_time_management;
+
+bool TimeManagement::initialized()
+{
+    return s_time_management != nullptr;
+}
+
+bool TimeManagement::is_system_timer(const HardwareTimer& timer) const
+{
+    return &timer == m_system_timer.ptr();
+}
+
+void TimeManagement::set_epoch_time(time_t value)
+{
+    InterruptDisabler disabler;
+    m_epoch_time = value;
+}
+
+time_t TimeManagement::epoch_time() const
+{
+    return m_epoch_time;
+}
+
+void TimeManagement::initialize(bool probe_non_legacy_hardware_timers)
+{
+    ASSERT(!TimeManagement::initialized());
+    s_time_management = new TimeManagement(probe_non_legacy_hardware_timers);
+}
+time_t TimeManagement::seconds_since_boot() const
+{
+    return m_seconds_since_boot;
+}
+time_t TimeManagement::ticks_per_second() const
+{
+    return m_system_timer->ticks_per_second();
+}
+
+time_t TimeManagement::ticks_this_second() const
+{
+    return m_ticks_this_second;
+}
+
+time_t TimeManagement::boot_time() const
+{
+    return RTC::boot_time();
+}
+
+void TimeManagement::stale_function(const RegisterState&)
+{
+}
+
+TimeManagement::TimeManagement(bool probe_non_legacy_hardware_timers)
+{
+    if (ACPI::Parser::the().is_operable()) {
+        if (!ACPI::Parser::the().x86_specific_flags().cmos_rtc_not_present) {
+            RTC::initialize();
+            m_epoch_time += boot_time();
+        } else {
+            klog() << "ACPI: RTC CMOS Not present";
+        }
+    } else {
+        // We just assume that we can access RTC CMOS, if ACPI isn't usable.
+        RTC::initialize();
+        m_epoch_time += boot_time();
+    }
+    if (probe_non_legacy_hardware_timers) {
+        if (!probe_and_set_non_legacy_hardware_timers())
+            if (!probe_and_set_legacy_hardware_timers())
+                ASSERT_NOT_REACHED();
+        return;
+    }
+    if (probe_and_set_legacy_hardware_timers())
+        return;
+    ASSERT_NOT_REACHED();
+}
+
+Vector<size_t> TimeManagement::scan_and_initialize_periodic_timers()
+{
+    bool enable_periodic_mode = is_hpet_periodic_mode_allowed();
+    dbg() << "Scanning for Periodic timers";
+    Vector<size_t> periodic_timers_indexes;
+    periodic_timers_indexes.ensure_capacity(m_hardware_timers.size());
+    for (size_t index = 0; index < m_hardware_timers.size(); index++) {
+        if (!m_hardware_timers[index].is_null()) {
+            if (m_hardware_timers[index]->is_periodic_capable()) {
+                periodic_timers_indexes.append(index);
+                if (enable_periodic_mode)
+                    m_hardware_timers[index]->set_periodic();
+            }
+        }
+    }
+    return periodic_timers_indexes;
+}
+
+Vector<size_t> TimeManagement::scan_for_non_periodic_timers()
+{
+    dbg() << "Scanning for Non-Periodic timers";
+    Vector<size_t> non_periodic_timers_indexes;
+    non_periodic_timers_indexes.ensure_capacity(m_hardware_timers.size());
+    for (size_t index = 0; index < m_hardware_timers.size(); index++) {
+        if (!m_hardware_timers[index].is_null())
+            if (!m_hardware_timers[index]->is_periodic_capable())
+                non_periodic_timers_indexes.append(index);
+    }
+    return non_periodic_timers_indexes;
+}
+
+bool TimeManagement::is_hpet_periodic_mode_allowed()
+{
+    if (!KParams::the().has("hpet")) {
+        return true;
+    }
+    auto hpet_mode = KParams::the().get("hpet");
+    if (hpet_mode == "periodic")
+        return true;
+    if (hpet_mode == "nonperiodic")
+        return false;
+    ASSERT_NOT_REACHED();
+}
+
+bool TimeManagement::probe_and_set_non_legacy_hardware_timers()
+{
+    if (!ACPI::Parser::the().is_operable())
+        return false;
+    if (!HPET::test_and_initialize())
+        return false;
+    if (!HPET::the().comparators().size()) {
+        dbg() << "HPET initialization aborted.";
+        return false;
+    }
+    dbg() << "HPET: Setting appropriate functions to timers.";
+
+    m_hardware_timers.resize(HPET::the().comparators().size());
+    for (size_t index = 0; index < m_hardware_timers.size(); index++) {
+        m_hardware_timers[index] = HPET::the().comparators()[index];
+#ifdef TIME_DEBUG
+        dbg() << m_hardware_timers[index].ptr() << " <- " << HPET::the().comparators()[index].ptr();
+#endif
+    }
+
+    auto periodic_timer_indexes = scan_and_initialize_periodic_timers();
+    auto non_periodic_timer_indexes = scan_for_non_periodic_timers();
+
+    if (is_hpet_periodic_mode_allowed())
+        ASSERT(!periodic_timer_indexes.is_empty());
+
+    ASSERT(periodic_timer_indexes.size() + non_periodic_timer_indexes.size() >= 2);
+
+    if (periodic_timer_indexes.size() >= 2) {
+        m_time_keeper_timer = m_hardware_timers[periodic_timer_indexes[1]];
+        m_system_timer = m_hardware_timers[periodic_timer_indexes[0]];
+    } else {
+        if (periodic_timer_indexes.size() == 1) {
+            m_time_keeper_timer = m_hardware_timers[periodic_timer_indexes[0]];
+            m_system_timer = m_hardware_timers[non_periodic_timer_indexes[0]];
+        } else {
+            m_time_keeper_timer = m_hardware_timers[non_periodic_timer_indexes[1]];
+            m_system_timer = m_hardware_timers[non_periodic_timer_indexes[0]];
+        }
+    }
+
+    m_system_timer->change_function([](const RegisterState& regs) { update_scheduler_ticks(regs); });
+    dbg() << "Reset timers";
+    m_system_timer->try_to_set_frequency(m_system_timer->calculate_nearest_possible_frequency(1024));
+    m_time_keeper_timer->change_function([](const RegisterState& regs) { update_time(regs); });
+    m_time_keeper_timer->try_to_set_frequency(OPTIMAL_TICKS_PER_SECOND_RATE);
+
+    return true;
+}
+
+bool TimeManagement::probe_and_set_legacy_hardware_timers()
+{
+    if (ACPI::Parser::the().is_operable()) {
+        if (ACPI::Parser::the().x86_specific_flags().cmos_rtc_not_present) {
+            dbg() << "ACPI: CMOS RTC Not Present";
+            return false;
+        } else {
+            dbg() << "ACPI: CMOS RTC Present";
+        }
+    }
+
+    m_hardware_timers[0] = PIT::initialize([](const RegisterState& regs) { update_time(regs); });
+    m_hardware_timers[1] = RealTimeClock::create([](const RegisterState& regs) { update_scheduler_ticks(regs); });
+    m_time_keeper_timer = m_hardware_timers[0];
+    m_system_timer = m_hardware_timers[1];
+    return true;
+}
+
+TimeManagement& TimeManagement::the()
+{
+    ASSERT(TimeManagement::initialized());
+    return *s_time_management;
+}
+
+void TimeManagement::update_time(const RegisterState& regs)
+{
+    TimeManagement::the().increment_time_since_boot(regs);
+}
+
+void TimeManagement::increment_time_since_boot(const RegisterState&)
+{
+    ASSERT(!m_time_keeper_timer.is_null());
+    if (++m_ticks_this_second >= m_time_keeper_timer->ticks_per_second()) {
+        // FIXME: Synchronize with other clock somehow to prevent drifting apart.
+        ++m_seconds_since_boot;
+        ++m_epoch_time;
+        m_ticks_this_second = 0;
+    }
+}
+
+void TimeManagement::update_scheduler_ticks(const RegisterState& regs)
+{
+    TimeManagement::the().update_ticks(regs);
+}
+
+void TimeManagement::update_ticks(const RegisterState& regs)
+{
+    Scheduler::timer_tick(regs);
+}
+}

Kernel/Time/TimeManagement.h

@@ -0,0 +1,82 @@
+/*
+ * Copyright (c) 2020, Liav A. <liavalb@hotmail.co.il>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice, this
+ *    list of conditions and the following disclaimer.
+ *
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+ * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+ * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include <AK/FixedArray.h>
+#include <AK/Optional.h>
+#include <AK/OwnPtr.h>
+#include <AK/Types.h>
+#include <AK/WeakPtr.h>
+#include <Kernel/UnixTypes.h>
+
+namespace Kernel {
+
+#define OPTIMAL_TICKS_PER_SECOND_RATE 1000
+
+class HardwareTimer;
+class TimeManagement {
+public:
+    static bool initialized();
+    static void initialize(bool probe_non_legacy_hardware_timers);
+    static TimeManagement& the();
+
+    time_t epoch_time() const;
+    void set_epoch_time(time_t);
+    time_t seconds_since_boot() const;
+    time_t ticks_per_second() const;
+    time_t ticks_this_second() const;
+    time_t boot_time() const;
+
+    bool is_system_timer(const HardwareTimer&) const;
+
+    static void update_time(const RegisterState&);
+    void increment_time_since_boot(const RegisterState&);
+
+    static void update_scheduler_ticks(const RegisterState& regs);
+    void update_ticks(const RegisterState&);
+
+    static void stale_function(const RegisterState&);
+    static bool is_hpet_periodic_mode_allowed();
+
+private:
+    explicit TimeManagement(bool probe_non_legacy_hardware_timers);
+    bool probe_and_set_legacy_hardware_timers();
+    bool probe_and_set_non_legacy_hardware_timers();
+    Vector<size_t> scan_and_initialize_periodic_timers();
+    Vector<size_t> scan_for_non_periodic_timers();
+    FixedArray<RefPtr<HardwareTimer>> m_hardware_timers { 2 };
+
+    u32 m_ticks_this_second { 0 };
+    u32 m_seconds_since_boot { 0 };
+    time_t m_epoch_time { 0 };
+    RefPtr<HardwareTimer> m_system_timer;
+    RefPtr<HardwareTimer> m_time_keeper_timer;
+    Function<void(RegisterState&)> m_scheduler_ticking { update_time };
+    Function<void(RegisterState&)> m_stale_method { stale_function };
+};
+
+}

Kernel/TimerQueue.h

@@ -30,7 +30,7 @@
 #include <AK/NonnullOwnPtr.h>
 #include <AK/OwnPtr.h>
 #include <AK/SinglyLinkedList.h>
-#include <Kernel/Devices/PIT.h>
+#include <Kernel/Time/TimeManagement.h>
 
 namespace Kernel {
 
@@ -53,9 +53,9 @@ struct Timer {
 };
 
 enum TimeUnit {
-    MS = TICKS_PER_SECOND / 1000,
-    S = TICKS_PER_SECOND,
-    M = TICKS_PER_SECOND * 60
+    MS = OPTIMAL_TICKS_PER_SECOND_RATE / 1000,
+    S = OPTIMAL_TICKS_PER_SECOND_RATE,
+    M = OPTIMAL_TICKS_PER_SECOND_RATE * 60
 };
 
 class TimerQueue {

Kernel/init.cpp

@@ -48,7 +48,6 @@
 #include <Kernel/Devices/MBVGADevice.h>
 #include <Kernel/Devices/NullDevice.h>
 #include <Kernel/Devices/PATAChannel.h>
-#include <Kernel/Devices/PIT.h>
 #include <Kernel/Devices/PS2MouseDevice.h>
 #include <Kernel/Devices/RandomDevice.h>
 #include <Kernel/Devices/SB16.h>
@@ -71,6 +70,7 @@
 #include <Kernel/Random.h>
 #include <Kernel/TTY/PTYMultiplexer.h>
 #include <Kernel/TTY/VirtualConsole.h>
+#include <Kernel/Time/TimeManagement.h>
 #include <Kernel/VM/MemoryManager.h>
 
 // Defined in the linker script
@@ -89,6 +89,7 @@ static void setup_acpi();
 static void setup_vmmouse();
 static void setup_pci();
 static void setup_interrupts();
+static void setup_time_management();
 
 VirtualConsole* tty0;
 
@@ -121,8 +122,7 @@ extern "C" [[noreturn]] void init()
 
     __stack_chk_guard = get_good_random<u32>();
 
-    PIT::initialize();
-    RTC::initialize();
+    setup_time_management();
 
     // call global constructors after gtd and itd init
     for (ctor_func_t* ctor = &start_ctors; ctor < &end_ctors; ctor++)
@@ -150,8 +150,6 @@ extern "C" [[noreturn]] void init()
 
     setup_pci();
 
-    PIT::initialize();
-
     if (text_debug) {
         dbg() << "Text mode enabled";
     } else {
@@ -178,7 +176,7 @@ extern "C" [[noreturn]] void init()
     Process::create_kernel_process(syncd_thread, "syncd", [] {
         for (;;) {
             VFS::the().sync();
-            Thread::current->sleep(1 * TICKS_PER_SECOND);
+            Thread::current->sleep(1 * TimeManagement::the().ticks_per_second());
         }
     });
 
@@ -482,4 +480,24 @@ void setup_interrupts()
     klog() << "smp boot argmuent has an invalid value.";
     hang();
 }
+
+void setup_time_management()
+{
+    if (!KParams::the().has("time")) {
+        TimeManagement::initialize(true);
+        return;
+    }
+    auto time = KParams::the().get("time");
+    if (time == "legacy") {
+        TimeManagement::initialize(false);
+        return;
+    }
+    if (time == "modern") {
+        TimeManagement::initialize(true);
+        return;
+    }
+
+    kprintf("time boot argmuent has an invalid value.\n");
+    hang();
+}
 }