Re: [PATCH] ARM: OMAP: timer32k: fix tick count calculation when reprogramming

[imre.deak@solidboot.com]

On Wed, Jul 05, 2006 at 01:51:04AM -0700, tony@atomide.com wrote:
> * imre.deak@solidboot.com <imre.deak@solidboot.com> [060703 08:51]:
> > Reprogramming takes places before putting the CPU into idle mode if
> > the dynamic tick option is enabled. The timer is then set to expire
> > at the next pending timer event. Because some time has already passed
> > since the last reported jiffy we have to wait less than the time
> > specified in jiffies.
> 
> Looks good to me. This patch seems to need an update though.

Sorry, the patch was against an older commit.. The updated one:

diff --git a/arch/arm/plat-omap/timer32k.c b/arch/arm/plat-omap/timer32k.c
index b0119f1..eba5946 100644
--- a/arch/arm/plat-omap/timer32k.c
+++ b/arch/arm/plat-omap/timer32k.c
@@ -106,6 +106,8 @@ static inline unsigned long omap_32k_tim
 
 static inline void omap_32k_timer_start(unsigned long load_val)
 {
+	if (!load_val)
+		load_val = 1;
 	omap_32k_timer_write(load_val, OMAP1_32K_TIMER_TVR);
 	omap_32k_timer_write(0x0f, OMAP1_32K_TIMER_CR);
 }
@@ -230,7 +232,15 @@ static irqreturn_t omap_32k_timer_interr
  */
 void omap_32k_timer_reprogram(unsigned long next_tick)
 {
-	omap_32k_timer_start(JIFFIES_TO_HW_TICKS(next_tick, 32768) + 1);
+	unsigned long ticks = JIFFIES_TO_HW_TICKS(next_tick, 32768) + 1;
+	unsigned long now = omap_32k_sync_timer_read();
+	unsigned long idled = now - omap_32k_last_tick;
+
+	if (idled + 1 < ticks)
+		ticks -= idled;
+	else
+		ticks = 1;
+	omap_32k_timer_start(ticks);
 }
 
 static struct irqaction omap_32k_timer_irq;

> 
> Did you do this to fix some specific problem, or just to improve timer
> accuracy?

It's about timer accuracy. Currently we are using the system timer
through the hrtimer API and need a 1 jiffy resolution.

--Imre

> 
> > Also make sure we don't set a load value of 0 whose outcome is
> > unspecified according to the TRM.
> 
> OK
> 
> Tony