Initial commit: SUB-OS 64-Bit Production Monolithic Operating System with LazyBox userland suite

arch/x86_64/cpu/pit.c

@@ -0,0 +1,49 @@
+#include <arch/x86_64/pit.h>
+#include <arch/x86_64/isr.h>
+#include <arch/x86_64/pic.h>
+#include <arch/x86_64/io.h>
+#include <kernel/sched.h>
+
+#define PIT_COMMAND_PORT 0x43
+#define PIT_CHANNEL0_PORT 0x40
+#define PIT_BASE_FREQUENCY 1193182
+
+static volatile uint64_t pit_ticks = 0;
+static uint32_t pit_freq = 100;
+
+static void pit_handler(registers_t* regs) {
+    (void)regs;
+    pit_ticks++;
+
+    // Notify preemptive scheduler
+    sched_tick();
+}
+
+void pit_init(uint32_t frequency) {
+    pit_freq = frequency;
+    uint32_t divisor = PIT_BASE_FREQUENCY / frequency;
+
+    // Channel 0, lobyte/hibyte, Rate generator (Mode 2)
+    outb(PIT_COMMAND_PORT, 0x36);
+    outb(PIT_CHANNEL0_PORT, (uint8_t)(divisor & 0xFF));
+    outb(PIT_CHANNEL0_PORT, (uint8_t)((divisor >> 8) & 0xFF));
+
+    // Register IRQ0 handler
+    isr_register_handler(32, pit_handler);
+    pic_clear_mask(0);
+}
+
+uint64_t pit_get_ticks(void) {
+    return pit_ticks;
+}
+
+uint64_t pit_get_uptime_ms(void) {
+    return (pit_ticks * 1000) / pit_freq;
+}
+
+void pit_sleep(uint32_t milliseconds) {
+    uint64_t target = pit_ticks + (milliseconds * pit_freq) / 1000;
+    while (pit_ticks < target) {
+        hlt();
+    }
+}