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Re: 2.6.19 timer API changes

To: linux-mips@linux-mips.org
Subject: Re: 2.6.19 timer API changes
From: Daniel Laird <danieljlaird@hotmail.com>
Date: Tue, 19 Dec 2006 06:51:48 -0800 (PST)
In-reply-to: <20061219.233410.25911550.anemo@mba.ocn.ne.jp>
Original-recipient: rfc822;linux-mips@linux-mips.org
References: <7925588.post@talk.nabble.com> <7943218.post@talk.nabble.com> <20061219.233410.25911550.anemo@mba.ocn.ne.jp>
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Atsushi Nemoto wrote:
> 
> Hmm, do the TIMER1 and CP0_COUNTER run at same speed?  If no, the
> PNX8550 port should be broken (i.e. gettimeofday() did not work
> properly) even without the timer API changes.  You should provide
> custom clocksource.mips_read (previously named mips_hpt_read) function
> which returns TIMER1 counter value.  If the TIMER1 was not 32-bit
> free-run counter, some trick would be required.  Refer sb1250 or
> jmr3927 for example.
> 
> ---
> Atsushi Nemoto
> 
> 
> 
I am just starting to look into this (thankyou for your first comments).
I have reduced the problem code, so if I change the following:
/* For use both as a high precision timer and an interrupt source.  */
static void __init c0_hpt_timer_init(void)
{
        expirelo = read_c0_count() + cycles_per_jiffy;
        write_c0_compare(expirelo);
} (the 2.6.19 version)
to the following:
/* For use both as a high precision timer and an interrupt source.  */
static void __init c0_hpt_timer_init(void)
{
    unsigned int count = read_c0_count() - mips_hpt_read();
        expirelo = (count / cycles_per_jiffy + 1) * cycles_per_jiffy;
        write_c0_count(expirelo - cycles_per_jiffy);
        write_c0_compare(expirelo);
        write_c0_count(count);
}

Then i get the system to boot up and all seems well.  I am new to this and
am looking into why this change makes the system boot up.  As always though
any help is appreciated.

Cheers
Dan
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