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The ep93xx has a weird timer tick base (983.04 kHz.) This experimental
patch tries to increase time of day accuracy by keeping the number of
ticks until the next jiffy in a fractional value representation.
Signed-off-by: Lennert Buytenhek <buytenh@wantstofly.org>
Index: linux-2.6.23-rc5/arch/arm/mach-ep93xx/core.c
===================================================================
--- linux-2.6.23-rc5.orig/arch/arm/mach-ep93xx/core.c 2007-09-04 02:26:38.000000000 +0200
+++ linux-2.6.23-rc5/arch/arm/mach-ep93xx/core.c 2007-09-04 02:26:48.000000000 +0200
@@ -94,19 +94,32 @@
* track of lost jiffies.
*/
static unsigned int last_jiffy_time;
+static unsigned int next_jiffy_time;
+static unsigned int accumulator;
-#define TIMER4_TICKS_PER_JIFFY ((CLOCK_TICK_RATE + (HZ/2)) / HZ)
+#define TIMER4_TICKS_PER_JIFFY (983040 / HZ)
+#define TIMER4_TICKS_MOD_JIFFY (983040 % HZ)
+
+static int after_eq(unsigned long a, unsigned long b)
+{
+ return ((signed long)(a - b)) >= 0;
+}
static int ep93xx_timer_interrupt(int irq, void *dev_id)
{
write_seqlock(&xtime_lock);
__raw_writel(1, EP93XX_TIMER1_CLEAR);
- while ((signed long)
- (__raw_readl(EP93XX_TIMER4_VALUE_LOW) - last_jiffy_time)
- >= TIMER4_TICKS_PER_JIFFY) {
- last_jiffy_time += TIMER4_TICKS_PER_JIFFY;
+ while (after_eq(__raw_readl(EP93XX_TIMER4_VALUE_LOW), next_jiffy_time)) {
timer_tick();
+
+ last_jiffy_time = next_jiffy_time;
+ next_jiffy_time += TIMER4_TICKS_PER_JIFFY;
+ accumulator += TIMER4_TICKS_MOD_JIFFY;
+ if (accumulator >= HZ) {
+ next_jiffy_time++;
+ accumulator -= HZ;
+ }
}
write_sequnlock(&xtime_lock);
Index: linux-2.6.23-rc5/include/asm-arm/arch-ep93xx/timex.h
===================================================================
--- linux-2.6.23-rc5.orig/include/asm-arm/arch-ep93xx/timex.h 2007-09-04 02:25:36.000000000 +0200
+++ linux-2.6.23-rc5/include/asm-arm/arch-ep93xx/timex.h 2007-09-04 02:26:48.000000000 +0200
@@ -2,4 +2,4 @@
* linux/include/asm-arm/arch-ep93xx/timex.h
*/
-#define CLOCK_TICK_RATE 983040
+#define CLOCK_TICK_RATE (1000 * HZ)
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