1 files changed, 84 insertions, 0 deletions
diff --git a/grub-core/kern/i386/tsc_pit.c b/grub-core/kern/i386/tsc_pit.c
new file mode 100644
index 0000000..67990bf
--- /dev/null
+++ b/grub-core/kern/i386/tsc_pit.c
@@ -0,0 +1,84 @@
+/* kern/i386/tsc.c - x86 TSC time source implementation
+ * Requires Pentium or better x86 CPU that supports the RDTSC instruction.
+ * This module uses the PIT 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>
+#include <grub/cpu/io.h>
+
+static int
+grub_pit_wait (void)
+{
+  int ret = 0;
+
+  /* Disable timer2 gate and speaker.  */
+  grub_outb (grub_inb (GRUB_PIT_SPEAKER_PORT)
+	     & ~ (GRUB_PIT_SPK_DATA | GRUB_PIT_SPK_TMR2),
+             GRUB_PIT_SPEAKER_PORT);
+
+  /* Set tics.  */
+  grub_outb (GRUB_PIT_CTRL_SELECT_2 | GRUB_PIT_CTRL_READLOAD_WORD,
+	     GRUB_PIT_CTRL);
+  /* 0xffff ticks: 55ms. */
+  grub_outb (0xff, GRUB_PIT_COUNTER_2);
+  grub_outb (0xff, GRUB_PIT_COUNTER_2);
+
+  /* Enable timer2 gate, keep speaker disabled.  */
+  grub_outb ((grub_inb (GRUB_PIT_SPEAKER_PORT) & ~ GRUB_PIT_SPK_DATA)
+	     | GRUB_PIT_SPK_TMR2,
+             GRUB_PIT_SPEAKER_PORT);
+
+  if ((grub_inb (GRUB_PIT_SPEAKER_PORT) & GRUB_PIT_SPK_TMR2_LATCH) == 0x00) {
+    ret = 1;
+    /* Wait.  */
+    while ((grub_inb (GRUB_PIT_SPEAKER_PORT) & GRUB_PIT_SPK_TMR2_LATCH) == 0x00);
+  }
+
+  /* Disable timer2 gate and speaker.  */
+  grub_outb (grub_inb (GRUB_PIT_SPEAKER_PORT)
+	     & ~ (GRUB_PIT_SPK_DATA | GRUB_PIT_SPK_TMR2),
+             GRUB_PIT_SPEAKER_PORT);
+
+  return ret;
+}
+
+/* Calibrate the TSC based on the RTC.  */
+int
+grub_tsc_calibrate_from_pit (void)
+{
+  /* First calibrate the TSC rate (relative, not absolute time). */
+  grub_uint64_t start_tsc, end_tsc;
+
+  start_tsc = grub_get_tsc ();
+  if (!grub_pit_wait ())
+    return 0;
+  end_tsc = grub_get_tsc ();
+
+  grub_tsc_rate = 0;
+  if (end_tsc > start_tsc)
+    grub_tsc_rate = grub_divmod64 ((55ULL << 32), end_tsc - start_tsc, 0);
+  if (grub_tsc_rate == 0)
+    return 0;
+  return 1;
+}