From: "Xiaogeng (Shawn) Jin" <xjin@redswitch•com>
To: Paul Mackerras <paulus@samba•org>
Cc: linuxppc-embedded@lists•linuxppc.org
Subject: Re: usage of disarm_decr[]
Date: Wed, 11 Dec 2002 14:31:50 -0800 [thread overview]
Message-ID: <3DF7BCD6.6080605@redswitch.com> (raw)
In-Reply-To: 15863.44615.245438.78166@argo.ozlabs.ibm.com
Thank you. I have some further questions regarding to timer_interrupt().
How often is timer_interrupt() invoked? Every 1/HZ seconds? This is
controlled by the decrementer, right? Initially the value of the
decrementer is 'tb_ticks_per_jiffy'. Then it's updated in
timer_interrupt(). Why isn't 'next_dec' the initial value
'tb_ticks_per_jiffy'? It's due to the time drift caused by the accuracy
of external clock (oscillator) or by the precision of software?
next_dec = tb_ticks_per_jiffy - tb_delta(&jiffy_stamp)
The timebase register is initialized to zero and then increments
periodically. How does it increment? Each clock (TMBCLK) the increment
is 1? by itself, I mean, hardware itself, or by software?
>>What's the purpose of using disarm_decr? I read the timer_interrupt()
>>code and found the only place where it's referenced.
>
> RT-Linux (www.fsmlabs.com) uses it. RT-Linux takes over all interrupt
> handling, including decrementer interrupts, and the disarm_decr thing
> is there to give RT-Linux a way to take control of the decrementer
> register.
Thanks.
- Shawn.
** Sent via the linuxppc-embedded mail list. See http://lists.linuxppc.org/
prev parent reply other threads:[~2002-12-11 22:31 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2002-12-11 21:13 usage of disarm_decr[] Xiaogeng (Shawn) Jin
2002-12-11 21:29 ` Paul Mackerras
2002-12-11 22:31 ` Xiaogeng (Shawn) Jin [this message]
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