kernel: add timers via pit

include/calcite/syscalls.h

@@ -36,3 +36,5 @@ enum fs_access_result read_file_splat(file_handle_t handle, void *buffer, uint64
 void wait_for_mouse_packet(struct mouse_packet *packet_out);
 
 void *map_pages(uint64_t count);
+
+void sleep_ms(uint64_t ms_to_sleep);

include/kernel-public/syscall-numbers.h

@@ -25,5 +25,6 @@ enum {
   SYSCALL_GET_FILE_SIZE,
   SYSCALL_READ_FILE,
   SYSCALL_WAIT_FOR_MOUSE_PACKET,
-  SYSCALL_MAP_PAGES
+  SYSCALL_MAP_PAGES,
+  SYSCALL_SLEEP_MS
 };

src/kernel/entry.c

@@ -25,6 +25,7 @@
 #include "paging.h"
 #include "input.h"
 #include "panic.h"
+#include "timer.h"
 #include "heap.h"
 #include "pata.h"
 #include "ps2.h"
@@ -243,9 +244,13 @@ static const char *cmdline_look_up(const char *key) {
 
   //set up interrupts
 
+  init_timer();
   init_ps2();
+
+  set_irq_handler(0x00, &on_pit_irq);
   set_irq_handler(0x01, &on_keyboard_irq);
   set_irq_handler(0x0c, &on_mouse_irq);
+
   enable_interrupts();
 
   //set up syscalls
@@ -259,6 +264,7 @@ static const char *cmdline_look_up(const char *key) {
   register_syscall(SYSCALL_READ_FILE, (void *)&syscall_read_file);
   register_syscall(SYSCALL_WAIT_FOR_MOUSE_PACKET, (void *)&syscall_wait_for_mouse_packet);
   register_syscall(SYSCALL_MAP_PAGES, (void *)&syscall_map_pages);
+  register_syscall(SYSCALL_SLEEP_MS, (void *)&syscall_sleep_ms);
 
   //probe for drives
 

src/kernel/timer.asm

@@ -0,0 +1,37 @@
+ ; Calcite, src/kernel/timer.asm
+ ; Copyright 2025 Benji Dial
+ ;
+ ; This program is free software: you can redistribute it and/or modify
+ ; it under the terms of the GNU General Public License as published by
+ ; the Free Software Foundation, either version 3 of the License, or
+ ; (at your option) any later version.
+ ;
+ ; This program is distributed in the hope that it will be useful, but
+ ; WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+ ; or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
+ ; for more details.
+ ;
+ ; You should have received a copy of the GNU General Public License along
+ ; with this program. If not, see <https://www.gnu.org/licenses/>.
+
+
+bits 64
+default rel
+
+section .text
+
+global init_timer
+init_timer:
+
+  ;generate an irq every 1193 cycles (~ every millisecond)
+
+  mov al, 0x34
+  out 0x43, al
+
+  mov al, 0xa9
+  out 0x40, al
+
+  mov al, 0x04
+  out 0x40, al
+
+  ret

src/kernel/timer.c

@@ -0,0 +1,93 @@
+/* Calcite, src/kernel/timer.c
+ * Copyright 2025 Benji Dial
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+ * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
+ * for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program. If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#include "scheduler.h"
+#include "timer.h"
+#include "heap.h"
+
+struct sleeping_list_entry {
+  struct sleeping_list_entry *next;
+  uint64_t sleeping_until;//pit irqs since boot
+  struct continuation_info continuation;
+};
+
+//entries are always sorted increasing by sleeping_until
+static struct sleeping_list_entry *first_entry = 0;
+static struct sleeping_list_entry *last_entry = 0;
+
+//pit irq happens ~ once per millisecond
+static uint64_t pit_irqs_since_boot = 0;
+
+void on_pit_irq() {
+
+  ++pit_irqs_since_boot;
+
+  while (first_entry != 0 && pit_irqs_since_boot >= first_entry->sleeping_until) {
+
+    add_to_queue(&ready_continuations, &first_entry->continuation);
+
+    struct sleeping_list_entry *old_first = first_entry;
+    first_entry = old_first->next;
+    heap_dealloc(old_first, sizeof(struct sleeping_list_entry));
+
+    if (first_entry == 0)
+      last_entry = 0;
+
+  }
+
+}
+
+//until in pit irqs since boot
+static void sleep_until(uint64_t until) {
+
+  struct sleeping_list_entry *entry = heap_alloc(sizeof(struct sleeping_list_entry));
+  entry->sleeping_until = until;
+
+  __asm__ ("cli");
+
+  if (first_entry == 0) {
+    entry->next = 0;
+    first_entry = entry;
+    last_entry = entry;
+  }
+
+  else if (first_entry->sleeping_until >= until) {
+    entry->next = first_entry;
+    first_entry = entry;
+  }
+
+  else if (last_entry->sleeping_until <= until) {
+    entry->next = 0;
+    last_entry->next = entry;
+    last_entry = entry;
+  }
+
+  else {
+    struct sleeping_list_entry *just_before = first_entry;
+    while (just_before->next->sleeping_until <= until)
+      just_before = just_before->next;
+    entry->next = just_before->next;
+    just_before->next = entry;
+  }
+
+  yield_sti(&entry->continuation);
+
+}
+
+void syscall_sleep_ms(uint64_t ms_to_sleep) {
+  sleep_until(pit_irqs_since_boot + ms_to_sleep);
+}

src/kernel/timer.h

@@ -0,0 +1,26 @@
+/* Calcite, src/kernel/timer.h
+ * Copyright 2025 Benji Dial
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+ * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
+ * for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program. If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+
+#include <stdint.h>
+
+void init_timer();
+
+void on_pit_irq();
+
+void syscall_sleep_ms(uint64_t ms_to_sleep);

src/user-apps/hello/hello.c

@@ -76,6 +76,8 @@ void main() {
 
   while (1) {
 
+    sleep_ms(10);
+
     struct mouse_packet packet;
     wait_for_mouse_packet(&packet);
 

src/user-libs/calcite/syscalls.c

@@ -60,3 +60,7 @@ void wait_for_mouse_packet(struct mouse_packet *packet_out) {
 void *map_pages(uint64_t count) {
   return (void *)do_syscall(count, 0, 0, SYSCALL_MAP_PAGES);
 }
+
+void sleep_ms(uint64_t ms_to_sleep) {
+  do_syscall(ms_to_sleep, 0, 0, SYSCALL_SLEEP_MS);
+}