1 files changed, 74 insertions, 0 deletions
diff --git a/grub-core/kern/i386/tsc.c b/grub-core/kern/i386/tsc.c
new file mode 100644
index 0000000..36b35e2
--- /dev/null
+++ b/grub-core/kern/i386/tsc.c
@@ -0,0 +1,74 @@
+/* kern/i386/tsc.c - x86 TSC time source implementation
+ * Requires Pentium or better x86 CPU that supports the RDTSC instruction.
+ * This module uses the RTC (via grub_get_rtc()) to calibrate the TSC to
+ * real time.
+ *
+ *  GRUB  --  GRand Unified Bootloader
+ *  Copyright (C) 2008  Free Software Foundation, Inc.
+ *
+ *  GRUB 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.
+ *
+ *  GRUB 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 GRUB.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include <grub/types.h>
+#include <grub/time.h>
+#include <grub/misc.h>
+#include <grub/i386/tsc.h>
+#include <grub/i386/pit.h>
+
+/* This defines the value TSC had at the epoch (that is, when we calibrated it). */
+static grub_uint64_t tsc_boot_time;
+
+/* Calibrated TSC rate.  (In TSC ticks per millisecond.) */
+static grub_uint64_t tsc_ticks_per_ms;
+
+
+grub_uint64_t
+grub_tsc_get_time_ms (void)
+{
+  return tsc_boot_time + grub_divmod64 (grub_get_tsc (), tsc_ticks_per_ms, 0);
+}
+
+
+/* How many RTC ticks to use for calibration loop. (>= 1) */
+#define CALIBRATION_TICKS 2
+
+/* Calibrate the TSC based on the RTC.  */
+static void
+calibrate_tsc (void)
+{
+  /* First calibrate the TSC rate (relative, not absolute time). */
+  grub_uint64_t start_tsc;
+  grub_uint64_t end_tsc;
+
+  start_tsc = grub_get_tsc ();
+  grub_pit_wait (0xffff);
+  end_tsc = grub_get_tsc ();
+
+  tsc_ticks_per_ms = grub_divmod64 (end_tsc - start_tsc, 55, 0);
+}
+
+void
+grub_tsc_init (void)
+{
+  if (grub_cpu_is_tsc_supported ())
+    {
+      tsc_boot_time = grub_get_tsc ();
+      calibrate_tsc ();
+      grub_install_get_time_ms (grub_tsc_get_time_ms);
+    }
+  else
+    {
+      grub_install_get_time_ms (grub_rtc_get_time_ms);
+    }
+}