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Re: jiffies

>
> please check the function named "timer_interrupts". The code is
> actully in the "do_timer" function.
> When timer interrupt occurs, ISR will update jiffies.
>
Yep, I just read it, but how the hardware timer is programmed, in other words,
where is the code that attach do_timer at hw timer?


Hi,

The hooking up of timer ISR is very board / architecture specific. I
currently am having a very MIPS specific 2.6.15 kernel code with me,
but still I can vaguely see how it is done in i386:

1) The do_timer() is called by do_timer_interrupt_hook()
(include/asm-i386/mach-default/do_timer.h)

2) It is called by do_timer_interrupt() (arch/i386/kernel/time.c)

3) Which in turn is called by timer_interrupt() in the same file.

Now this timer_interrupt is actually the timer ISR which needs to be
hooked onto the particular irq.

4) Instead of doing this with request_irq(), following low level
interfaces are used:

static struct irqaction irq0  = { timer_interrupt, SA_INTERRUPT,
CPU_MASK_NONE, "timer", NULL, NULL};

void __init time_init_hook(void)
{
       setup_irq(0, &irq0);
}

Thanks,

Rajat

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