[kernel] Add HPET support, create clock class

Create a clock class which can be queried for current timestamp in
nanoseconds. Also implements a simple HPET class as one possible clock
source.

Tags: time

src/kernel/hpet.h

@@ -0,0 +1,50 @@
+#pragma once
+/// \file hpet.h
+/// Definitions for handling the HPET timer
+
+#include <stdint.h>
+
+/// Source function for the clock that takes a pointer to
+/// an hpet object.
+uint64_t hpet_clock_source(void *);
+
+/// Represents a single HPET timer
+class hpet
+{
+public:
+	/// Constructor.
+	/// \arg index  The index of the HPET out of all HPETs
+	/// \arg base   The base address of the HPET for MMIO
+	hpet(uint8_t index, uint64_t *base);
+
+	/// Configure the timer and start it running.
+	void enable();
+
+	/// Wait in a tight loop while reading the HPET counter.
+	/// \arg ns  Number of nanoseconds to wait
+	void spinwait(uint64_t ns) const;
+
+	/// Get the timer rate in ticks per ns
+	inline uint64_t rate() const { return m_period * 1000000ull; }
+
+	/// Get the current timer value
+	uint64_t value() const;
+
+private:
+	friend void hpet_irq_callback(void *);
+	friend uint64_t hpet_clock_source(void *);
+
+	void setup_timer_interrupts(unsigned timer, uint8_t irq, uint64_t interval, bool periodic);
+	void enable_timer(unsigned timer);
+	void disable_timer(unsigned timer);
+
+	void callback();
+
+	uint8_t m_timers;
+	uint8_t m_index;
+
+	uint64_t m_period;
+	volatile uint64_t *m_base;
+};
+
+