5 files changed, 110 insertions, 19 deletions

diff --git a/src/kernel/arch/amd64/acpi.c b/src/kernel/arch/amd64/acpi.c
new file mode 100644
index 0000000..cc7791f
--- /dev/null
+++ b/src/kernel/arch/amd64/acpi.c
@@ -0,0 +1,68 @@
+#include <kernel/arch/amd64/acpi.h>
+#include <kernel/panic.h>
+#include <shared/mem.h>
+#include <stdint.h>
+
+typedef struct {
+	char sig[8];
+	uint8_t checksum;
+	char oemid[6];
+	uint8_t rev;
+	uint32_t rsdt;
+} __attribute__((packed)) RDSP;
+
+typedef struct {
+	char sig[4];
+	uint32_t len;
+	uint8_t rev;
+	uint8_t checksum;
+	char oemID[6];
+	char oemTID[8];
+	uint32_t oemRev;
+	uint32_t creatorId;
+	uint32_t creatorRev;
+	char data[0];
+} __attribute__((packed)) SDT;
+
+/* https://www.intel.com/content/dam/www/public/us/en/documents/technical-specifications/software-developers-hpet-spec-1-0a.pdf */
+typedef struct {
+	uint8_t where;
+	uint8_t bitwidth;
+	uint8_t bitoffset;
+	uint8_t _reserved;
+	uint64_t addr;
+} __attribute__((packed)) GAS; /* Generic Address Structure */
+
+typedef struct {
+	SDT hdr;
+	uint32_t _someid;
+	GAS addr;
+	/* ... */
+} __attribute__((packed)) HPET;
+
+void
+acpi_parse(const void *rdsp_v)
+{
+	const RDSP *rdsp = rdsp_v;
+	if (memcmp(rdsp->sig, "RSD PTR ", 8) != 0) {
+		panic_invalid_state();
+	}
+
+	SDT *rsdt = (void*)(uintptr_t)rdsp->rsdt;
+	if (memcmp(rsdt->sig, "RSDT ", 4) != 0) {
+		panic_invalid_state();
+	}
+
+	uint32_t *sub = (void*)rsdt->data;
+	int len = (rsdt->len - sizeof(SDT)) / 4;
+	for (int i = 0; i < len; i++) {
+		SDT *it = (void*)(uintptr_t)sub[i];
+		if (memcmp(it->sig, "HPET", 4) == 0) {
+			HPET *hpet = (void*)it;
+			GAS *gas = &hpet->addr;
+			if (gas->where == 0) { /* in memory */
+				hpet_init((void*)gas->addr);
+			}
+		}
+	}
+}
diff --git a/src/kernel/arch/amd64/acpi.h b/src/kernel/arch/amd64/acpi.h
new file mode 100644
index 0000000..138bf41
--- /dev/null
+++ b/src/kernel/arch/amd64/acpi.h
@@ -0,0 +1,4 @@
+#pragma once
+
+void acpi_parse(const void *rsdp);
+void hpet_init(void *base);
diff --git a/src/kernel/arch/amd64/boot.c b/src/kernel/arch/amd64/boot.c
index 337d23b..330a11e 100644
--- a/src/kernel/arch/amd64/boot.c
+++ b/src/kernel/arch/amd64/boot.c
@@ -1,4 +1,5 @@
 #include <kernel/arch/amd64/3rdparty/multiboot2.h>
+#include <kernel/arch/amd64/acpi.h>
 #include <kernel/arch/amd64/boot.h>
 #include <kernel/arch/amd64/driver/driver.h>
 #include <kernel/arch/amd64/driver/serial.h>
@@ -71,6 +72,12 @@ void kmain_early(void *mbi) {
 	video_init(vid);
 	pata_init();
 
+	{
+		struct multiboot_tag_old_acpi *mod;
+		mod = mbi_tag(mbi, MULTIBOOT_TAG_TYPE_ACPI_OLD);
+		acpi_parse(mod->rsdp);
+	}
+
 	kprintf("pci...\n");
 	pci_init();
 
diff --git a/src/kernel/arch/amd64/time.c b/src/kernel/arch/amd64/time.c
index f4fa744..ef76249 100644
--- a/src/kernel/arch/amd64/time.c
+++ b/src/kernel/arch/amd64/time.c
@@ -1,31 +1,49 @@
+#include <kernel/arch/amd64/acpi.h>
 #include <kernel/arch/amd64/boot.h>
 #include <kernel/arch/amd64/interrupts.h>
-#include <kernel/arch/amd64/time.h>
 #include <kernel/panic.h>
 #include <kernel/proc.h>
 
-static uint64_t uptime = 0, goal = ~0;
 static Proc *scheduled = NULL;
 
-uint64_t uptime_ms(void) { return uptime; }
+static void *hpet = NULL;
+static uint64_t hpet_period;
 
-static void update_goal(void) {
-	goal = scheduled ? scheduled->waits4timer.goal : ~(uint64_t)0;
+void hpet_init(void *base) {
+	if (hpet) panic_invalid_state();
+	hpet = base;
+
+	uint64_t *info = hpet;
+	uint64_t *cfg = hpet + 0x10;
+	hpet_period = *info >> 32;
+	*cfg |= 1<<0; /* enable */
 }
 
-void pit_irq(void) {
-	// TODO inefficient - getting here executes a lot of code which could just be a few lines of asm
-	uptime++;
-	if (uptime < goal) return;
+uint64_t uptime_ns(void) {
+	if (hpet == NULL) panic_invalid_state();
+	uint64_t *counter = hpet + 0xF0;
+	unsigned __int128 femto = *counter * hpet_period;
+	uint64_t nano = femto / 1000000;
+	return nano;
+}
 
+static void pit_irq(void) {
 	Proc *p = scheduled;
-	assert(p);
-	scheduled = p->waits4timer.next;
-	proc_setstate(p, PS_RUNNING);
-	update_goal();
+	if (p && p->waits4timer.goal < uptime_ns()) {
+		scheduled = p->waits4timer.next;
+		proc_setstate(p, PS_RUNNING);
+	}
 }
 
+
 void timer_schedule(Proc *p, uint64_t time) {
+	uint64_t now = uptime_ns();
+	/* to prevent leaking the current uptime, saturate instead of overflowing */
+	time = now + time;
+	if (time < now) {
+		time = ~0;
+	}
+
 	proc_setstate(p, PS_WAITS4TIMER);
 	p->waits4timer.goal = time;
 
@@ -36,7 +54,6 @@ void timer_schedule(Proc *p, uint64_t time) {
 	}
 	p->waits4timer.next = *slot;
 	*slot = p;
-	update_goal();
 }
 
 void timer_deschedule(Proc *p) {
@@ -49,7 +66,6 @@ void timer_deschedule(Proc *p) {
 	*slot = p->waits4timer.next;
 
 	proc_setstate(p, PS_RUNNING);
-	update_goal();
 }
 
 void timer_init(void) {
diff --git a/src/kernel/arch/amd64/time.h b/src/kernel/arch/amd64/time.h
deleted file mode 100644
index 04ba9b0..0000000
--- a/src/kernel/arch/amd64/time.h
+++ /dev/null
@@ -1,4 +0,0 @@
-#pragma once
-#include <kernel/arch/generic.h>
-
-void pit_irq(void);