Am Montag, den 02.04.2007, 13:34 +0200 schrieb Richard Cochran:
> > Then you have to implement it like I described. 
> > 
> > Take a look at the implementation for integrator-platforms.
> > (Timer with wraparound)
> 
> Well, as I said, the IXP425 one-shot timer mode does _not_ wrap around.
> It just stops.

> I'm not sure how (or why) to account for the clock ticks that transpire
> during the interrupt handler.
> 
> There are no clock ticks lost in __ipipe_mach_get_tsc, since this gets the
> value of a free-flowing timer.
> 
> Previously you wrote,
> 
> > These lost-ticks should be added to the global time-stamp (returned by
> > get_tsc) and should mentioned at the linux-gettimeoffset-function also.
> 
> Can you be more specific? What is the "linux-gettimeoffset-function" of
> which you speak?

Linux gettimeoffset calls a march-specific function
(ixp4xx_gettimeoffset) which delivers the time in us since the last
timer-tick (timer-interrupt).

> > Lost-ticks could sum up to a bothering time-error.
> 
> But in the plain-old Linux code, no such adjustment is made (using a
> periodic timer, see below).

In this implementation a time-stamp register is used. Excuse me, I
misunderstood your mail before...
Forget what i said. It's quite simpler to use such a timer for adeos. 
Gilles Chanteperdrix is right.

> 
> Does the Linux IXP4xx timer code have a bug?
> 
> Richard
> 
> 
> linux-2.6.19/arch/arm/mach-ixp4xx/common.c, from line 223:
> 
> /*************************************************************************
>  * IXP4xx timer tick
>  * We use OS timer1 on the CPU for the timer tick and the timestamp 
>  * counter as a source of real clock ticks to account for missed jiffies.
>  *************************************************************************/
> 
> static unsigned volatile last_jiffy_time;
> 
> #define CLOCK_TICKS_PER_USEC	((CLOCK_TICK_RATE + USEC_PER_SEC/2) / USEC_PER_SEC)
> 
> static irqreturn_t ixp4xx_timer_interrupt(int irq, void *dev_id)
> {
> 	write_seqlock(&xtime_lock);
> 
> 	/* Clear Pending Interrupt by writing '1' to it */
> 	*IXP4XX_OSST = IXP4XX_OSST_TIMER_1_PEND;
> 
> 	/*
> 	 * Catch up with the real idea of time
> 	 */
> 	while ((signed long)(*IXP4XX_OSTS - last_jiffy_time) >= LATCH) {
> 		timer_tick();
> 		last_jiffy_time += LATCH;
> 	}
> 
> 	write_sequnlock(&xtime_lock);
> 
> 	return IRQ_HANDLED;
> }
> 
> static struct irqaction ixp4xx_timer_irq = {
> 	.name		= "IXP4xx Timer Tick",
> 	.flags		= IRQF_DISABLED | IRQF_TIMER,
> 	.handler	= ixp4xx_timer_interrupt,
> };
> 
> static void __init ixp4xx_timer_init(void)
> {
> 	/* Clear Pending Interrupt by writing '1' to it */
> 	*IXP4XX_OSST = IXP4XX_OSST_TIMER_1_PEND;
> 
> 	/* Setup the Timer counter value */
> 	*IXP4XX_OSRT1 = (LATCH & ~IXP4XX_OST_RELOAD_MASK) | IXP4XX_OST_ENABLE;
> 
> 	/* Reset time-stamp counter */
> 	*IXP4XX_OSTS = 0;
> 	last_jiffy_time = 0;
> 
> 	/* Connect the interrupt handler and enable the interrupt */
> 	setup_irq(IRQ_IXP4XX_TIMER1, &ixp4xx_timer_irq);
> }
> 
> > 
> > 
> > - Manfred Schlaegl
> > 

- Manfred Schlaegl