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authorLinus Torvalds <torvalds@ppc970.osdl.org>2005-04-16 15:20:36 -0700
committerLinus Torvalds <torvalds@ppc970.osdl.org>2005-04-16 15:20:36 -0700
commit1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 (patch)
tree0bba044c4ce775e45a88a51686b5d9f90697ea9d /include/asm-mips/timex.h
Linux-2.6.12-rc2
Initial git repository build. I'm not bothering with the full history, even though we have it. We can create a separate "historical" git archive of that later if we want to, and in the meantime it's about 3.2GB when imported into git - space that would just make the early git days unnecessarily complicated, when we don't have a lot of good infrastructure for it. Let it rip!
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diff --git a/include/asm-mips/timex.h b/include/asm-mips/timex.h
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+/*
+ * This file is subject to the terms and conditions of the GNU General Public
+ * License. See the file "COPYING" in the main directory of this archive
+ * for more details.
+ *
+ * Copyright (C) 1998, 1999, 2003 by Ralf Baechle
+ */
+#ifndef _ASM_TIMEX_H
+#define _ASM_TIMEX_H
+
+#include <asm/mipsregs.h>
+
+/*
+ * This is the frequency of the timer used for Linux's timer interrupt.
+ * The value should be defined as accurate as possible or under certain
+ * circumstances Linux timekeeping might become inaccurate or fail.
+ *
+ * For many system the exact clockrate of the timer isn't known but due to
+ * the way this value is used we can get away with a wrong value as long
+ * as this value is:
+ *
+ * - a multiple of HZ
+ * - a divisor of the actual rate
+ *
+ * 500000 is a good such cheat value.
+ *
+ * The obscure number 1193182 is the same as used by the original i8254
+ * time in legacy PC hardware; the chip unfortunately also found in a
+ * bunch of MIPS systems. The last remaining user of the i8254 for the
+ * timer interrupt is the RM200; it's a very standard system so there is
+ * no reason to make this a separate architecture.
+ */
+
+#include <timex.h>
+
+/*
+ * Standard way to access the cycle counter.
+ * Currently only used on SMP for scheduling.
+ *
+ * Only the low 32 bits are available as a continuously counting entity.
+ * But this only means we'll force a reschedule every 8 seconds or so,
+ * which isn't an evil thing.
+ *
+ * We know that all SMP capable CPUs have cycle counters.
+ */
+
+typedef unsigned int cycles_t;
+
+static inline cycles_t get_cycles (void)
+{
+ return read_c0_count();
+}
+
+#endif /* _ASM_TIMEX_H */