timekeeper: redo timekeeping

kernel-src/include/kernel/timekeeper.h

@@ -2,9 +2,40 @@
 #define _TIMEKEEPER_H
 
 #include <time.h>
+#include <stdbool.h>
 
-void timekeeper_init(time_t (*tick)(), time_t ticksperus);
-timespec_t timekeeper_timefromboot();
-timespec_t timekeeper_time();
+#define TIMEKEEPER_SOURCE_FLAGS_EARLY 1 // can be used as an early timer
+
+typedef struct {
+	time_t ticks_per_us;
+	void *private;
+} timekeeper_source_info_t;
+
+typedef struct {
+	const char *name;
+	int priority;
+	bool (*probe)(void); // returns true if the timer can currently be used
+	timekeeper_source_info_t *(*init)(void); // initializes the timer, returning the info structure
+	time_t (*ticks)(timekeeper_source_info_t *private); // returns a monotonic number of ticks
+	int flags;
+} timekeeper_source_t;
+
+// initializes the highest priority source that can be used as an early timer and switches the cpu to use it
+void timekeeper_early_init(time_t us_offset);
+
+// initializes the highest priority source and switches the cpu to use it. uses the early timer for calibration if nescessary
+void timekeeper_init(void);
+
+// spins waiting for us to pass
+void timekeeper_wait_us(time_t us);
+
+timespec_t timekeeper_timefromboot(void);
+timespec_t timekeeper_time(void);
+
+#define TIMEKEEPER_SOURCE(x, ...) \
+	static timekeeper_source_t x = { \
+		__VA_ARGS__ \
+	}; \
+	__attribute__((section(".timekeeper_sources"), used)) static timekeeper_source_t *timekeeper_source_##x = &x;
 
 #endif