1 files changed, 41 insertions, 0 deletions
diff --git a/src/pit.cpp b/src/pit.cpp
new file mode 100644
index 0000000..964522b
--- /dev/null
+++ b/src/pit.cpp
@@ -0,0 +1,41 @@
+#include "pit.hpp"
+#include "idt.hpp"
+#include "portio.hpp"
+#include "tasking.hpp"
+
+constexpr std::uint32_t Frequency = 1000;
+
+static volatile std::uint32_t ticks = 0;
+
+static void timer_callback(const Registers& regs)
+{
+    ticks = ticks + 1;
+
+    schedule(regs);
+}
+
+void pit_initialize()
+{
+   // Firstly, register our timer callback.
+   idt_register_callback(32, timer_callback);
+
+   // The value we send to the PIT is the value to divide it's input clock
+   // (1193180 Hz) by, to get our required frequency. Important to note is
+   // that the divisor must be small enough to fit into 16-bits.
+   const auto divisor = 1193180ul / Frequency;
+
+   // Send the command byte.
+   outb(0x43, 0x36);
+
+   // Send the frequency divisor.
+   outb(0x40, divisor & 0xFF);
+   outb(0x40, (divisor >> 8) & 0xFF);
+}
+
+void pit_delay_ms(std::int32_t ms)
+{
+    const auto end = ticks + ms;
+    while (static_cast<std::int32_t>(end - ticks) > 0)
+        asm volatile("nop");
+}
+