TSC on coreboot (Re: [PATCH] High resolution time/TSC patch v3)

[Robert Millan <rmh@aybabtu.com>]

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On Sun, Aug 03, 2008 at 09:48:16PM +0200, Robert Millan wrote:
> On Mon, Jul 28, 2008 at 10:05:33AM -0700, Colin D Bennett wrote:
> > +/* Calibrate the TSC based on the RTC.  */
> > +static void
> > +calibrate_tsc (void)
> > +{
> > +  /* First calbrate the TSC rate (relative, not absolute time). */
> > +  grub_uint64_t start_tsc;
> > +  grub_uint64_t end_tsc;
> > +  grub_uint32_t initial_tick;
> > +  grub_uint32_t start_tick;
> > +  grub_uint32_t end_tick;
> > +
> > +  /* Wait for the start of the next tick;
> > +     we'll base out timing off this edge. */
> > +  initial_tick = grub_get_rtc ();
> 
> Ah, I see the problem.  It calls grub_get_rtc() which in grub-coreboot is just
> a stub.
> 
> How about using the interval timer for calibration instead?

Here.  With this patch your code works on coreboot too.

Note:  AFAICT we can't calculate the epoch without RTC.  But then again, this
epoch is just as defined by the time BIOS enables RTC interrupts, so why not
define it ourselves?  I propose that we define epoch as the time in which our
TSC code is initialized.

If knowing the time in which BIOS was started is really useful, maybe we could
#ifdef it instead.  Though if it's not I'd prefer the simplicity.

-- 
Robert Millan

  The DRM opt-in fallacy: "Your data belongs to us. We will decide when (and
  how) you may access your data; but nobody's threatening your freedom: we
  still allow you to remove your data and not access it at all."

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diff -Nurp -x .svn -x '*.mk' -x '*~' ../grub2.tsc/conf/i386-coreboot.rmk ./conf/i386-coreboot.rmk
--- ../grub2.tsc/conf/i386-coreboot.rmk	2008-08-04 00:19:11.000000000 +0200
+++ ./conf/i386-coreboot.rmk	2008-08-04 01:40:37.000000000 +0200
@@ -18,6 +18,9 @@ kernel_elf_SOURCES = kern/i386/linuxbios
 	kern/misc.c kern/mm.c kern/loader.c kern/rescue.c kern/term.c \
 	kern/time.c \
 	kern/i386/dl.c kern/parser.c kern/partition.c \
+	kern/i386/tsc.c kern/i386/pit.c \
+	kern/generic/rtc_get_time_ms.c \
+	kern/generic/millisleep.c \
 	kern/env.c \
 	term/i386/pc/console.c \
 	term/i386/pc/at_keyboard.c term/i386/pc/vga_text.c \
diff -Nurp -x .svn -x '*.mk' -x '*~' ../grub2.tsc/conf/i386-pc.rmk ./conf/i386-pc.rmk
--- ../grub2.tsc/conf/i386-pc.rmk	2008-08-04 00:19:11.000000000 +0200
+++ ./conf/i386-pc.rmk	2008-08-04 01:21:32.000000000 +0200
@@ -44,7 +44,7 @@ kernel_img_SOURCES = kern/i386/pc/startu
 	kern/misc.c kern/mm.c kern/loader.c kern/rescue.c kern/term.c \
 	kern/time.c \
 	kern/i386/dl.c kern/i386/pc/init.c kern/parser.c kern/partition.c \
-	kern/i386/tsc.c \
+	kern/i386/tsc.c kern/i386/pit.c \
 	kern/generic/rtc_get_time_ms.c \
 	kern/generic/millisleep.c \
 	kern/env.c \
diff -Nurp -x .svn -x '*.mk' -x '*~' ../grub2.tsc/include/grub/i386/pit.h ./include/grub/i386/pit.h
--- ../grub2.tsc/include/grub/i386/pit.h	1970-01-01 01:00:00.000000000 +0100
+++ ./include/grub/i386/pit.h	2008-08-04 01:22:12.000000000 +0200
@@ -0,0 +1,19 @@
+/*
+ *  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/>.
+ */
+
+extern void grub_pit_wait (grub_uint16_t tics);
diff -Nurp -x .svn -x '*.mk' -x '*~' ../grub2.tsc/kern/i386/linuxbios/init.c ./kern/i386/linuxbios/init.c
--- ../grub2.tsc/kern/i386/linuxbios/init.c	2008-08-04 00:19:11.000000000 +0200
+++ ./kern/i386/linuxbios/init.c	2008-08-04 00:31:45.000000000 +0200
@@ -61,11 +61,6 @@ grub_stop_floppy (void)
 }
 
 void
-grub_millisleep (grub_uint32_t ms __attribute__ ((unused)))
-{
-}
-
-void
 grub_exit (void)
 {
   grub_printf ("grub_exit() is not implemented.\n");
@@ -144,7 +139,7 @@ grub_machine_init (void)
   /* This variable indicates size, not offset.  */
   grub_upper_mem -= GRUB_MEMORY_MACHINE_UPPER_START;
 
-  grub_install_get_time_ms (grub_rtc_get_time_ms);
+  grub_tsc_init ();
 }
 
 void
diff -Nurp -x .svn -x '*.mk' -x '*~' ../grub2.tsc/kern/i386/pit.c ./kern/i386/pit.c
--- ../grub2.tsc/kern/i386/pit.c	1970-01-01 01:00:00.000000000 +0100
+++ ./kern/i386/pit.c	2008-08-04 01:27:07.000000000 +0200
@@ -0,0 +1,39 @@
+/*
+ *  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/cpu/io.h>
+
+#define TIMER2_REG_CONTROL	0x42
+#define TIMER_REG_COMMAND	0x43
+#define TIMER2_REG_LATCH	0x61
+
+#define TIMER2_SELECT		0x80
+#define TIMER_ENABLE_LSB	0x20
+#define TIMER_ENABLE_MSB	0x10
+#define TIMER2_LATCH		0x20
+
+void
+grub_pit_wait (grub_uint16_t tics)
+{
+  grub_outb (TIMER2_SELECT | TIMER_ENABLE_LSB | TIMER_ENABLE_MSB, TIMER_REG_COMMAND);
+  grub_outb (tics & 0xff, TIMER2_REG_CONTROL);
+  grub_outb (tics >> 8, TIMER2_REG_CONTROL);
+
+  while ((grub_inb (TIMER2_REG_LATCH) & TIMER2_LATCH) == 0x00);
+}
diff -Nurp -x .svn -x '*.mk' -x '*~' ../grub2.tsc/kern/i386/tsc.c ./kern/i386/tsc.c
--- ../grub2.tsc/kern/i386/tsc.c	2008-08-04 00:19:11.000000000 +0200
+++ ./kern/i386/tsc.c	2008-08-04 01:36:51.000000000 +0200
@@ -25,8 +25,7 @@
 #include <grub/misc.h>
 #include <grub/i386/tsc.h>
 
-/* Calibrated reference for TSC=0.  This defines the time since the epoch in 
-   milliseconds that TSC=0 refers to. */
+/* 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.) */
@@ -47,44 +46,15 @@ grub_tsc_get_time_ms (void)
 static void
 calibrate_tsc (void)
 {
-  /* First calbrate the TSC rate (relative, not absolute time). */
+  /* First calibrate the TSC rate (relative, not absolute time). */
   grub_uint64_t start_tsc;
   grub_uint64_t end_tsc;
-  grub_uint32_t initial_tick;
-  grub_uint32_t start_tick;
-  grub_uint32_t end_tick;
-
-  /* Wait for the start of the next tick;
-     we'll base out timing off this edge. */
-  initial_tick = grub_get_rtc ();
-  do
-    {
-      start_tick = grub_get_rtc ();
-    }
-  while (start_tick == initial_tick);
-  start_tsc = grub_get_tsc ();
 
-  /* Wait for the start of the next tick.  This will
-     be the end of the 1-tick period. */
-  do
-    {
-      end_tick = grub_get_rtc ();
-    }
-  while (end_tick - start_tick < CALIBRATION_TICKS);
+  start_tsc = grub_get_tsc ();
+  grub_pit_wait (0xffff);
   end_tsc = grub_get_tsc ();
 
-  tsc_ticks_per_ms =
-    grub_divmod64 (grub_divmod64
-                   (end_tsc - start_tsc, end_tick - start_tick, 0)
-                   * GRUB_TICKS_PER_SECOND, 1000, 0);
-
-  /* Reference the TSC zero (boot time) to the epoch to 
-     get an absolute real time reference. */
-  grub_uint64_t ms_since_boot = grub_divmod64 (end_tsc, tsc_ticks_per_ms, 0);
-  grub_uint64_t mstime_now = grub_divmod64 ((grub_uint64_t) 1000 * end_tick,
-                                            GRUB_TICKS_PER_SECOND,
-                                            0);
-  tsc_boot_time = mstime_now - ms_since_boot;
+  tsc_ticks_per_ms = grub_divmod64 (end_tsc - start_tsc, 55, 0);
 }
 
 void
@@ -92,6 +62,7 @@ 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);
     }