kernel: initial timekeeper implementation

kernel-src/arch/x86-64/main.c

@@ -12,6 +12,7 @@
 #include <arch/acpi.h>
 #include <arch/apic.h>
 #include <arch/hpet.h>
+#include <kernel/timekeeper.h>
 
 static cpu_t bsp_cpu;
 
@@ -30,6 +31,8 @@ void kernel_entry() {
 	arch_acpi_init();
 	arch_apic_init();
 	arch_apic_initap();
-	arch_hpet_init();
+	// XXX fall back to another clock source
+	time_t u = arch_hpet_init();
+	timekeeper_init(arch_hpet_ticks, u);
 	__assert(!"kernel entry end");
 }

kernel-src/include/kernel/timekeeper.h

@@ -0,0 +1,10 @@
+#ifndef _TIMEKEEPER_H
+#define _TIMEKEEPER_H
+
+#include <time.h>
+
+void timekeeper_init(time_t (*tick)(), time_t ticksperus);
+timespec_t timekeeper_timefromboot();
+timespec_t timekeeper_time();
+
+#endif

kernel-src/sys/timekeeper.c

@@ -0,0 +1,41 @@
+#include <kernel/timekeeper.h>
+#include <limine.h>
+#include <logging.h>
+
+static volatile struct limine_boot_time_request timereq = {
+	.id = LIMINE_BOOT_TIME_REQUEST,
+	.revision = 0
+};
+
+static time_t bootunix;
+static time_t ticksperus;
+static time_t (*clockticks)();
+static time_t initclockticks;
+
+timespec_t timekeeper_timefromboot() {
+	timespec_t ts;
+	time_t ticks = clockticks() - initclockticks;
+	time_t uspassed = ticks / ticksperus;
+	ts.s = uspassed / 1000000;
+	ts.ns = (uspassed * 1000) % 1000000000;
+	return ts;
+}
+
+timespec_t timekeeper_time() {
+	timespec_t fromboot = timekeeper_timefromboot();
+	timespec_t unix;
+	unix.s = bootunix;
+	unix.ns = 0;
+	return timespec_add(unix, fromboot);
+}
+
+// tick is a function that returns the amount of ticks since the timer's initialisation
+void timekeeper_init(time_t (*tick)(), time_t _ticksperus) {
+	__assert(timereq.response);
+	bootunix = timereq.response->boot_time;
+	printf("timekeeper: unix time at boot: %lu\n", bootunix);
+	initclockticks = tick();
+	ticksperus = _ticksperus;
+	clockticks = tick;
+	printf("timekeeper: %lu clock ticks at init (%lu ticks per us)\n", initclockticks, ticksperus);
+}