From: Ralf Baechle <ralf@linux-mips.org>
To: Florian Fainelli <ffainelli@freebox.fr>
Cc: loody <miloody@gmail.com>,
Linux MIPS Mailing List <linux-mips@linux-mips.org>
Subject: Re: some questions about mips timer
Date: Tue, 6 Mar 2012 21:27:12 +0100 [thread overview]
Message-ID: <20120306202712.GM4519@linux-mips.org> (raw)
In-Reply-To: <160192556.459513.1331042510355.JavaMail.root@zmc>
On Tue, Mar 06, 2012 at 03:01:50PM +0100, Florian Fainelli wrote:
> > hi all:
> > I have some questions about mips_hpt_frequency:
> > 1. is mips_hpt_frequency == mips cpu frequency?
>
> No, it is usually cpu frequency / 2.
The architecture specification leaves the counter clock rate up up to the
implementation and only says the clock rate is a function of the pipeline
clock. In all reality this means the counter is running at the full or
half frequency. Just don't build on it,
clock := pipeline_clock * next_weeks_lottery_number % 42
would by compliant ;-)
On some CPUs the frequency can even be selected through a configuration
bitstream at reset time so you can't always count on a fixed relation
between CPU clock and count rate.
Some older CPU manuals contain a confusing wording saying the counter
increments at half (or full) instruction issue rate. That just means the
pipeline clock, no reason to be confused.
Ralf
next prev parent reply other threads:[~2012-03-06 20:27 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-03-06 13:48 some questions about mips timer loody
2012-03-06 14:01 ` Florian Fainelli
2012-03-06 20:27 ` Ralf Baechle [this message]
2012-03-06 20:33 ` David Daney
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