kernel: Rework the timer subsystem to count in microseconds

kernel/src/arch/Timer.cpp

@@ -58,7 +58,7 @@ namespace Timer
 {
     void tick()
     {
-        timer_ticks++;
+        timer_ticks += ARCH_TIMER_RESOLUTION;
     }
 
     usize raw_ticks()
@@ -68,20 +68,17 @@ namespace Timer
 
     usize ticks()
     {
-        return ticks_ms() / 1000;
+        return ticks_us() / US_PER_SECOND;
     }
 
     usize ticks_ms()
     {
-        return timer_ticks / ARCH_TIMER_FREQ;
+        return timer_ticks / 1000;
     }
 
-    usize ticks_us() // We want a bit of precision; if there are 10 ticks/ms, do not return the truncated ms value *
+    usize ticks_us()
-                     // 1000, but ticks * 100 (1000/10), which is more precise
     {
-        if constexpr (ARCH_TIMER_FREQ > 1000) return timer_ticks / (ARCH_TIMER_FREQ / 1000);
+        return timer_ticks;
-        else
-            return timer_ticks * (1000 / ARCH_TIMER_FREQ);
     }
 
     usize ticks_ns()
@@ -91,22 +88,22 @@ namespace Timer
 
     usize boot()
     {
-        return boot_timestamp;
+        return boot_timestamp / US_PER_SECOND;
     }
 
     usize boot_ms()
     {
-        return boot_timestamp * MS_PER_SECOND;
+        return boot_timestamp / 1000;
     }
 
     usize boot_us()
     {
-        return boot_timestamp * US_PER_SECOND;
+        return boot_timestamp;
     }
 
     usize boot_ns()
     {
-        return boot_timestamp * NS_PER_SECOND;
+        return boot_timestamp * 1000;
     }
 
     usize clock()
@@ -131,14 +128,12 @@ namespace Timer
 
     void init()
     {
-        boot_timestamp = bootloader_time_to_unix(bootboot.datetime);
+        boot_timestamp = bootloader_time_to_unix(bootboot.datetime) * US_PER_SECOND;
         arch_init();
     }
 }
 
-static_assert(IsPowerOfTwo<usize, ARCH_TIMER_FREQ>, "ARCH_TIMER_FREQ must be a power of two");
-
 bool should_invoke_scheduler()
 {
-    return (timer_ticks % ARCH_TIMER_FREQ) == 0;
+    return (timer_ticks % 1000) == 0;
 }

kernel/src/arch/x86_64/Timer.cpp

@@ -7,8 +7,8 @@ const u64 base_frequency = 1193182;
 
 void Timer::arch_init()
 {
-    constexpr u16 divisor = (u16)(base_frequency / (ARCH_TIMER_FREQ * 1000));
+    constexpr u16 divisor = (u16)(base_frequency / ((1000 / ARCH_TIMER_RESOLUTION) * 1000));
-    static_assert(divisor >= 100, "ARCH_TIMER_FREQ is too high");
+    static_assert(divisor >= 100, "ARCH_TIMER_RESOLUTION is too low");
     IO::outb(PIT_CHANNEL_0, (u8)(divisor & 0xFF));
     IO::outb(0x80, 0); // short delay
     IO::outb(PIT_CHANNEL_0, (u8)((divisor & 0xFF00) >> 8));

kernel/src/arch/x86_64/Timer.h

@@ -1,4 +1,5 @@
 #pragma once
 #include <luna/Types.h>
 
-const usize ARCH_TIMER_FREQ = 4;
+// Every timer tick is equivalent to 250 microseconds.
+const usize ARCH_TIMER_RESOLUTION = 250;